diff --git a/.eslintignore b/.eslintignore
deleted file mode 100644
index 62562b74a3b..00000000000
--- a/.eslintignore
+++ /dev/null
@@ -1,2 +0,0 @@
-coverage
-node_modules
diff --git a/.eslintrc.yml b/.eslintrc.yml
deleted file mode 100644
index f9359bf2892..00000000000
--- a/.eslintrc.yml
+++ /dev/null
@@ -1,14 +0,0 @@
-root: true
-env:
-  es2022: true
-  node: true
-rules:
-  eol-last: error
-  eqeqeq: [error, allow-null]
-  indent: [error, 2, { MemberExpression: "off", SwitchCase: 1 }]
-  no-trailing-spaces: error
-  no-unused-vars: [error, { vars: all, args: none, ignoreRestSiblings: true }]
-  no-restricted-globals:
-    - error
-    - name: Buffer
-      message: Use `import { Buffer } from "node:buffer"` instead of the global Buffer.
diff --git a/benchmarks/middleware.js b/benchmarks/middleware.js
index fed97ba8ce4..e05ec643e81 100644
--- a/benchmarks/middleware.js
+++ b/benchmarks/middleware.js
@@ -1,20 +1,19 @@
-
-var express = require('..');
-var app = express();
+const express = require('../')
+const app = express()
 
 // number of middleware
 
-var n = parseInt(process.env.MW || '1', 10);
-console.log('  %s middleware', n);
+let n = parseInt(process.env.MW || '1', 10)
+console.log('  %s middleware', n)
 
 while (n--) {
-  app.use(function(req, res, next){
-    next();
-  });
+  app.use((req, res, next) => {
+    next()
+  })
 }
 
-app.use(function(req, res){
+app.use((req, res) => {
   res.send('Hello World')
-});
+})
 
-app.listen(3333);
+app.listen(3333)
diff --git a/eslint.config.mjs b/eslint.config.mjs
new file mode 100644
index 00000000000..66661be5427
--- /dev/null
+++ b/eslint.config.mjs
@@ -0,0 +1,23 @@
+import globals from 'globals'
+import neostandard from 'neostandard'
+
+// globals present in Node.js but not in browsers.
+const nodeGlobals = Object.keys(globals.node).filter(g => !Object.keys(globals.browser).includes(g))
+
+// Node.js-specific globals that are allowed.
+const allowedGlobals = [
+  'require', 'module', 'exports', '__dirname', 'process', 'setImmediate'
+]
+
+export default [
+  ...neostandard({
+    env: ['mocha']
+  }),
+  {
+    rules: {
+      'global-require': 'warn',
+      'no-restricted-globals': ['error', ...nodeGlobals.filter(g => !allowedGlobals.includes(g))],
+      'n/handle-callback-err': 'off'
+    }
+  }
+]
diff --git a/examples/auth/index.js b/examples/auth/index.js
index 40b73e6de16..a6e2d641f4f 100644
--- a/examples/auth/index.js
+++ b/examples/auth/index.js
@@ -4,17 +4,17 @@
  * Module dependencies.
  */
 
-var express = require('../..');
-var hash = require('pbkdf2-password')()
-var path = require('node:path');
-var session = require('express-session');
+const express = require('../../')
+const hash = require('pbkdf2-password')()
+const path = require('node:path')
+const session = require('express-session')
 
-var app = module.exports = express();
+const app = module.exports = express()
 
 // config
 
-app.set('view engine', 'ejs');
-app.set('views', path.join(__dirname, 'views'));
+app.set('view engine', 'ejs')
+app.set('views', path.join(__dirname, 'views'))
 
 // middleware
 
@@ -23,112 +23,111 @@ app.use(session({
   resave: false, // don't save session if unmodified
   saveUninitialized: false, // don't create session until something stored
   secret: 'shhhh, very secret'
-}));
+}))
 
 // Session-persisted message middleware
 
-app.use(function(req, res, next){
-  var err = req.session.error;
-  var msg = req.session.success;
-  delete req.session.error;
-  delete req.session.success;
-  res.locals.message = '';
-  if (err) res.locals.message = '<p class="msg error">' + err + '</p>';
-  if (msg) res.locals.message = '<p class="msg success">' + msg + '</p>';
-  next();
-});
+app.use((req, res, next) => {
+  const err = req.session.error
+  const msg = req.session.success
+  delete req.session.error
+  delete req.session.success
+  res.locals.message = ''
+  if (err) res.locals.message = '<p class="msg error">' + err + '</p>'
+  if (msg) res.locals.message = '<p class="msg success">' + msg + '</p>'
+  next()
+})
 
 // dummy database
 
-var users = {
+const users = {
   tj: { name: 'tj' }
-};
+}
 
 // when you create a user, generate a salt
 // and hash the password ('foobar' is the pass here)
 
-hash({ password: 'foobar' }, function (err, pass, salt, hash) {
-  if (err) throw err;
+hash({ password: 'foobar' }, (err, pass, salt, hash) => {
+  if (err) throw err
   // store the salt & hash in the "db"
-  users.tj.salt = salt;
-  users.tj.hash = hash;
-});
-
+  users.tj.salt = salt
+  users.tj.hash = hash
+})
 
 // Authenticate using our plain-object database of doom!
 
-function authenticate(name, pass, fn) {
-  if (!module.parent) console.log('authenticating %s:%s', name, pass);
-  var user = users[name];
+function authenticate (name, pass, fn) {
+  if (!module.parent) console.log('authenticating %s:%s', name, pass)
+  const user = users[name]
   // query the db for the given username
   if (!user) return fn(null, null)
   // apply the same algorithm to the POSTed password, applying
   // the hash against the pass / salt, if there is a match we
   // found the user
-  hash({ password: pass, salt: user.salt }, function (err, pass, salt, hash) {
-    if (err) return fn(err);
+  hash({ password: pass, salt: user.salt }, (err, pass, salt, hash) => {
+    if (err) return fn(err)
     if (hash === user.hash) return fn(null, user)
     fn(null, null)
-  });
+  })
 }
 
-function restrict(req, res, next) {
+function restrict (req, res, next) {
   if (req.session.user) {
-    next();
+    next()
   } else {
-    req.session.error = 'Access denied!';
-    res.redirect('/login');
+    req.session.error = 'Access denied!'
+    res.redirect('/login')
   }
 }
 
-app.get('/', function(req, res){
-  res.redirect('/login');
-});
+app.get('/', (req, res) => {
+  res.redirect('/login')
+})
 
-app.get('/restricted', restrict, function(req, res){
-  res.send('Wahoo! restricted area, click to <a href="/logout">logout</a>');
-});
+app.get('/restricted', restrict, (req, res) => {
+  res.send('Wahoo! restricted area, click to <a href="/logout">logout</a>')
+})
 
-app.get('/logout', function(req, res){
+app.get('/logout', (req, res) => {
   // destroy the user's session to log them out
   // will be re-created next request
-  req.session.destroy(function(){
-    res.redirect('/');
-  });
-});
+  req.session.destroy(() => {
+    res.redirect('/')
+  })
+})
 
-app.get('/login', function(req, res){
-  res.render('login');
-});
+app.get('/login', (req, res) => {
+  res.render('login')
+})
 
-app.post('/login', function (req, res, next) {
+app.post('/login', (req, res, next) => {
   if (!req.body) return res.sendStatus(400)
-  authenticate(req.body.username, req.body.password, function(err, user){
+  authenticate(req.body.username, req.body.password, (err, user) => {
     if (err) return next(err)
     if (user) {
       // Regenerate session when signing in
       // to prevent fixation
-      req.session.regenerate(function(){
+      req.session.regenerate(() => {
         // Store the user's primary key
         // in the session store to be retrieved,
         // or in this case the entire user object
-        req.session.user = user;
-        req.session.success = 'Authenticated as ' + user.name
-          + ' click to <a href="/logout">logout</a>. '
-          + ' You may now access <a href="/restricted">/restricted</a>.';
-        res.redirect(req.get('Referrer') || '/');
-      });
+        req.session.user = user
+        req.session.success = 'Authenticated as ' + user.name +
+          ' click to <a href="/logout">logout</a>. ' +
+          ' You may now access <a href="/restricted">/restricted</a>.'
+        res.redirect(req.get('Referrer') || '/')
+      })
     } else {
-      req.session.error = 'Authentication failed, please check your '
-        + ' username and password.'
-        + ' (use "tj" and "foobar")';
-      res.redirect('/login');
+      req.session.error = 'Authentication failed, please check your ' +
+        ' username and password.' +
+        ' (use "tj" and "foobar")'
+      res.redirect('/login')
     }
-  });
-});
+  })
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/content-negotiation/db.js b/examples/content-negotiation/db.js
index f59b23bf18e..501e84966a1 100644
--- a/examples/content-negotiation/db.js
+++ b/examples/content-negotiation/db.js
@@ -1,9 +1,9 @@
 'use strict'
 
-var users = [];
+const users = []
 
-users.push({ name: 'Tobi' });
-users.push({ name: 'Loki' });
-users.push({ name: 'Jane' });
+users.push({ name: 'Tobi' })
+users.push({ name: 'Loki' })
+users.push({ name: 'Jane' })
 
-module.exports = users;
+module.exports = users
diff --git a/examples/content-negotiation/index.js b/examples/content-negotiation/index.js
index 280a4e22998..c417499d07a 100644
--- a/examples/content-negotiation/index.js
+++ b/examples/content-negotiation/index.js
@@ -1,46 +1,43 @@
 'use strict'
 
-var express = require('../../');
-var app = module.exports = express();
-var users = require('./db');
+const express = require('../../')
+const app = module.exports = express()
+const users = require('./db')
 
 // so either you can deal with different types of formatting
 // for expected response in index.js
-app.get('/', function(req, res){
+app.get('/', (req, res) => {
   res.format({
-    html: function(){
-      res.send('<ul>' + users.map(function(user){
-        return '<li>' + user.name + '</li>';
-      }).join('') + '</ul>');
+    html: function () {
+      res.send('<ul>' + users.map((user) => '<li>' + user.name + '</li>').join('') + '</ul>')
     },
 
-    text: function(){
-      res.send(users.map(function(user){
-        return ' - ' + user.name + '\n';
-      }).join(''));
+    text: function () {
+      res.send(users.map((user) => ' - ' + user.name + '\n').join(''))
     },
 
-    json: function(){
-      res.json(users);
+    json: function () {
+      res.json(users)
     }
-  });
-});
+  })
+})
 
 // or you could write a tiny middleware like
 // this to add a layer of abstraction
 // and make things a bit more declarative:
 
-function format(path) {
-  var obj = require(path);
-  return function(req, res){
-    res.format(obj);
-  };
+function format (path) {
+  // eslint-disable-next-line global-require
+  const obj = require(path)
+  return function (req, res) {
+    res.format(obj)
+  }
 }
 
-app.get('/users', format('./users'));
+app.get('/users', format('./users'))
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/content-negotiation/users.js b/examples/content-negotiation/users.js
index fe703e73a9a..e6badf7aafc 100644
--- a/examples/content-negotiation/users.js
+++ b/examples/content-negotiation/users.js
@@ -1,19 +1,15 @@
 'use strict'
 
-var users = require('./db');
+const users = require('./db')
 
-exports.html = function(req, res){
-  res.send('<ul>' + users.map(function(user){
-    return '<li>' + user.name + '</li>';
-  }).join('') + '</ul>');
-};
+exports.html = function (req, res) {
+  res.send('<ul>' + users.map((user) => '<li>' + user.name + '</li>').join('') + '</ul>')
+}
 
-exports.text = function(req, res){
-  res.send(users.map(function(user){
-    return ' - ' + user.name + '\n';
-  }).join(''));
-};
+exports.text = function (req, res) {
+  res.send(users.map((user) => ' - ' + user.name + '\n').join(''))
+}
 
-exports.json = function(req, res){
-  res.json(users);
-};
+exports.json = function (req, res) {
+  res.json(users)
+}
diff --git a/examples/cookie-sessions/index.js b/examples/cookie-sessions/index.js
index 83b6faee82b..51d310543ab 100644
--- a/examples/cookie-sessions/index.js
+++ b/examples/cookie-sessions/index.js
@@ -4,22 +4,22 @@
  * Module dependencies.
  */
 
-var cookieSession = require('cookie-session');
-var express = require('../../');
+const cookieSession = require('cookie-session')
+const express = require('../../')
 
-var app = module.exports = express();
+const app = module.exports = express()
 
 // add req.session cookie support
-app.use(cookieSession({ secret: 'manny is cool' }));
+app.use(cookieSession({ secret: 'manny is cool' }))
 
 // do something with the session
-app.get('/', function (req, res) {
+app.get('/', (req, res) => {
   req.session.count = (req.session.count || 0) + 1
   res.send('viewed ' + req.session.count + ' times\n')
 })
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/cookies/index.js b/examples/cookies/index.js
index 0620cb40e45..135f4e4f0dd 100644
--- a/examples/cookies/index.js
+++ b/examples/cookies/index.js
@@ -4,10 +4,10 @@
  * Module dependencies.
  */
 
-var express = require('../../');
-var app = module.exports = express();
-var logger = require('morgan');
-var cookieParser = require('cookie-parser');
+const express = require('../../')
+const app = module.exports = express()
+const logger = require('morgan')
+const cookieParser = require('cookie-parser')
 
 // custom log format
 if (process.env.NODE_ENV !== 'test') app.use(logger(':method :url'))
@@ -16,38 +16,38 @@ if (process.env.NODE_ENV !== 'test') app.use(logger(':method :url'))
 // req.cookies and req.signedCookies
 // when the secret is passed, used
 // for signing the cookies.
-app.use(cookieParser('my secret here'));
+app.use(cookieParser('my secret here'))
 
 // parses x-www-form-urlencoded
 app.use(express.urlencoded())
 
-app.get('/', function(req, res){
+app.get('/', (req, res) => {
   if (req.cookies.remember) {
-    res.send('Remembered :). Click to <a href="/forget">forget</a>!.');
+    res.send('Remembered :). Click to <a href="/forget">forget</a>!.')
   } else {
-    res.send('<form method="post"><p>Check to <label>'
-      + '<input type="checkbox" name="remember"/> remember me</label> '
-      + '<input type="submit" value="Submit"/>.</p></form>');
+    res.send('<form method="post"><p>Check to <label>' +
+      '<input type="checkbox" name="remember"/> remember me</label> ' +
+      '<input type="submit" value="Submit"/>.</p></form>')
   }
-});
+})
 
-app.get('/forget', function(req, res){
-  res.clearCookie('remember');
-  res.redirect(req.get('Referrer') || '/');
-});
+app.get('/forget', (req, res) => {
+  res.clearCookie('remember')
+  res.redirect(req.get('Referrer') || '/')
+})
 
-app.post('/', function(req, res){
-  var minute = 60000;
+app.post('/', (req, res) => {
+  const minute = 60000
 
   if (req.body && req.body.remember) {
     res.cookie('remember', 1, { maxAge: minute })
   }
 
-  res.redirect(req.get('Referrer') || '/');
-});
+  res.redirect(req.get('Referrer') || '/')
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/downloads/index.js b/examples/downloads/index.js
index ddc549ffec7..ac39b5da939 100644
--- a/examples/downloads/index.js
+++ b/examples/downloads/index.js
@@ -4,37 +4,37 @@
  * Module dependencies.
  */
 
-var express = require('../../');
-var path = require('node:path');
+const express = require('../../')
+const path = require('node:path')
 
-var app = module.exports = express();
+const app = module.exports = express()
 
 // path to where the files are stored on disk
-var FILES_DIR = path.join(__dirname, 'files')
+const FILES_DIR = path.join(__dirname, 'files')
 
-app.get('/', function(req, res){
+app.get('/', (req, res) => {
   res.send('<ul>' +
     '<li>Download <a href="/files/notes/groceries.txt">notes/groceries.txt</a>.</li>' +
     '<li>Download <a href="/files/amazing.txt">amazing.txt</a>.</li>' +
     '<li>Download <a href="/files/missing.txt">missing.txt</a>.</li>' +
     '<li>Download <a href="/files/CCTV大赛上海分赛区.txt">CCTV大赛上海分赛区.txt</a>.</li>' +
     '</ul>')
-});
+})
 
 // /files/* is accessed via req.params[0]
 // but here we name it :file
-app.get('/files/*file', function (req, res, next) {
-  res.download(req.params.file.join('/'), { root: FILES_DIR }, function (err) {
-    if (!err) return; // file sent
-    if (err.status !== 404) return next(err); // non-404 error
+app.get('/files/*file', (req, res, next) => {
+  res.download(req.params.file.join('/'), { root: FILES_DIR }, (err) => {
+    if (!err) return // file sent
+    if (err.status !== 404) return next(err) // non-404 error
     // file for download not found
-    res.statusCode = 404;
-    res.send('Cant find that file, sorry!');
-  });
-});
+    res.statusCode = 404
+    res.send('Cant find that file, sorry!')
+  })
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/ejs/index.js b/examples/ejs/index.js
index 0940d0624fb..c65db86eb82 100644
--- a/examples/ejs/index.js
+++ b/examples/ejs/index.js
@@ -4,10 +4,10 @@
  * Module dependencies.
  */
 
-var express = require('../../');
-var path = require('node:path');
+const express = require('../../')
+const path = require('node:path')
 
-var app = module.exports = express();
+const app = module.exports = express()
 
 // Register ejs as .html. If we did
 // not call this, we would need to
@@ -20,38 +20,38 @@ var app = module.exports = express();
 // we simply pass _any_ function, in this
 // case `ejs.__express`.
 
-app.engine('.html', require('ejs').__express);
+app.engine('.html', require('ejs').__express)
 
 // Optional since express defaults to CWD/views
 
-app.set('views', path.join(__dirname, 'views'));
+app.set('views', path.join(__dirname, 'views'))
 
 // Path to our public directory
 
-app.use(express.static(path.join(__dirname, 'public')));
+app.use(express.static(path.join(__dirname, 'public')))
 
 // Without this you would need to
 // supply the extension to res.render()
 // ex: res.render('users.html').
-app.set('view engine', 'html');
+app.set('view engine', 'html')
 
 // Dummy users
-var users = [
+const users = [
   { name: 'tobi', email: 'tobi@learnboost.com' },
   { name: 'loki', email: 'loki@learnboost.com' },
   { name: 'jane', email: 'jane@learnboost.com' }
-];
+]
 
-app.get('/', function(req, res){
+app.get('/', (req, res) => {
   res.render('users', {
-    users: users,
-    title: "EJS example",
-    header: "Some users"
-  });
-});
+    users,
+    title: 'EJS example',
+    header: 'Some users'
+  })
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/error-pages/index.js b/examples/error-pages/index.js
index 0863120bc8f..6a2bbdb08dc 100644
--- a/examples/error-pages/index.js
+++ b/examples/error-pages/index.js
@@ -4,51 +4,51 @@
  * Module dependencies.
  */
 
-var express = require('../../');
-var path = require('node:path');
-var app = module.exports = express();
-var logger = require('morgan');
-var silent = process.env.NODE_ENV === 'test'
+const express = require('../../')
+const path = require('node:path')
+const app = module.exports = express()
+const logger = require('morgan')
+const silent = process.env.NODE_ENV === 'test'
 
 // general config
-app.set('views', path.join(__dirname, 'views'));
-app.set('view engine', 'ejs');
+app.set('views', path.join(__dirname, 'views'))
+app.set('view engine', 'ejs')
 
 // our custom "verbose errors" setting
 // which we can use in the templates
 // via settings['verbose errors']
-app.enable('verbose errors');
+app.enable('verbose errors')
 
 // disable them in production
 // use $ NODE_ENV=production node examples/error-pages
 if (app.settings.env === 'production') app.disable('verbose errors')
 
-silent || app.use(logger('dev'));
+silent || app.use(logger('dev'))
 
 // Routes
 
-app.get('/', function(req, res){
-  res.render('index.ejs');
-});
+app.get('/', (req, res) => {
+  res.render('index.ejs')
+})
 
-app.get('/404', function(req, res, next){
+app.get('/404', (req, res, next) => {
   // trigger a 404 since no other middleware
   // will match /404 after this one, and we're not
   // responding here
-  next();
-});
+  next()
+})
 
-app.get('/403', function(req, res, next){
+app.get('/403', (req, res, next) => {
   // trigger a 403 error
-  var err = new Error('not allowed!');
-  err.status = 403;
-  next(err);
-});
+  const err = new Error('not allowed!')
+  err.status = 403
+  next(err)
+})
 
-app.get('/500', function(req, res, next){
+app.get('/500', (req, res, next) => {
   // trigger a generic (500) error
-  next(new Error('keyboard cat!'));
-});
+  next(new Error('keyboard cat!'))
+})
 
 // Error handlers
 
@@ -60,8 +60,8 @@ app.get('/500', function(req, res, next){
 // $ curl http://localhost:3000/notfound -H "Accept: application/json"
 // $ curl http://localhost:3000/notfound -H "Accept: text/plain"
 
-app.use(function(req, res, next){
-  res.status(404);
+app.use((req, res, next) => {
+  res.status(404)
 
   res.format({
     html: function () {
@@ -74,7 +74,7 @@ app.use(function(req, res, next){
       res.type('txt').send('Not found')
     }
   })
-});
+})
 
 // error-handling middleware, take the same form
 // as regular middleware, however they require an
@@ -88,16 +88,16 @@ app.use(function(req, res, next){
 // would remain being executed, however here
 // we simply respond with an error page.
 
-app.use(function(err, req, res, next){
+app.use((err, req, res, next) => {
   // we may use properties of the error object
   // here and next(err) appropriately, or if
   // we possibly recovered from the error, simply next().
-  res.status(err.status || 500);
-  res.render('500', { error: err });
-});
+  res.status(err.status || 500)
+  res.render('500', { error: err })
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/error/index.js b/examples/error/index.js
index d733a81172d..c0eb982511f 100644
--- a/examples/error/index.js
+++ b/examples/error/index.js
@@ -4,12 +4,12 @@
  * Module dependencies.
  */
 
-var express = require('../../');
-var logger = require('morgan');
-var app = module.exports = express();
-var test = app.get('env') === 'test'
+const express = require('../../')
+const logger = require('morgan')
+const app = module.exports = express()
+const test = app.get('env') === 'test'
 
-if (!test) app.use(logger('dev'));
+if (!test) app.use(logger('dev'))
 
 // error handling middleware have an arity of 4
 // instead of the typical (req, res, next),
@@ -17,37 +17,37 @@ if (!test) app.use(logger('dev'));
 // middleware, you may have several of them,
 // in different orders etc.
 
-function error(err, req, res, next) {
+function error (err, req, res, next) {
   // log it
-  if (!test) console.error(err.stack);
+  if (!test) console.error(err.stack)
 
   // respond with 500 "Internal Server Error".
-  res.status(500);
-  res.send('Internal Server Error');
+  res.status(500)
+  res.send('Internal Server Error')
 }
 
-app.get('/', function () {
+app.get('/', () => {
   // Caught and passed down to the errorHandler middleware
-  throw new Error('something broke!');
-});
+  throw new Error('something broke!')
+})
 
-app.get('/next', function(req, res, next){
+app.get('/next', (req, res, next) => {
   // We can also pass exceptions to next()
   // The reason for process.nextTick() is to show that
   // next() can be called inside an async operation,
   // in real life it can be a DB read or HTTP request.
-  process.nextTick(function(){
-    next(new Error('oh no!'));
-  });
-});
+  process.nextTick(() => {
+    next(new Error('oh no!'))
+  })
+})
 
 // the error handler is placed after routes
 // if it were above it would not receive errors
 // from app.get() etc
-app.use(error);
+app.use(error)
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/hello-world/index.js b/examples/hello-world/index.js
index 8c1855c2eb7..5236bc13e5a 100644
--- a/examples/hello-world/index.js
+++ b/examples/hello-world/index.js
@@ -1,15 +1,15 @@
 'use strict'
 
-var express = require('../../');
+const express = require('../../')
 
-var app = module.exports = express()
+const app = module.exports = express()
 
-app.get('/', function(req, res){
-  res.send('Hello World');
-});
+app.get('/', (req, res) => {
+  res.send('Hello World')
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/markdown/index.js b/examples/markdown/index.js
index 53e40ac38e4..5330c3236bc 100644
--- a/examples/markdown/index.js
+++ b/examples/markdown/index.js
@@ -4,41 +4,39 @@
  * Module dependencies.
  */
 
-var escapeHtml = require('escape-html');
-var express = require('../..');
-var fs = require('node:fs');
-var marked = require('marked');
-var path = require('node:path');
+const escapeHtml = require('escape-html')
+const express = require('../../')
+const fs = require('node:fs')
+const marked = require('marked')
+const path = require('node:path')
 
-var app = module.exports = express();
+const app = module.exports = express()
 
 // register .md as an engine in express view system
 
-app.engine('md', function(path, options, fn){
-  fs.readFile(path, 'utf8', function(err, str){
-    if (err) return fn(err);
-    var html = marked.parse(str).replace(/\{([^}]+)\}/g, function(_, name){
-      return escapeHtml(options[name] || '');
-    });
-    fn(null, html);
-  });
-});
+app.engine('md', (path, options, fn) => {
+  fs.readFile(path, 'utf8', (err, str) => {
+    if (err) return fn(err)
+    const html = marked.parse(str).replace(/\{([^}]+)\}/g, (_, name) => escapeHtml(options[name] || ''))
+    fn(null, html)
+  })
+})
 
-app.set('views', path.join(__dirname, 'views'));
+app.set('views', path.join(__dirname, 'views'))
 
 // make it the default, so we don't need .md
-app.set('view engine', 'md');
+app.set('view engine', 'md')
 
-app.get('/', function(req, res){
-  res.render('index', { title: 'Markdown Example' });
-});
+app.get('/', (req, res) => {
+  res.render('index', { title: 'Markdown Example' })
+})
 
-app.get('/fail', function(req, res){
-  res.render('missing', { title: 'Markdown Example' });
-});
+app.get('/fail', (req, res) => {
+  res.render('missing', { title: 'Markdown Example' })
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/multi-router/controllers/api_v1.js b/examples/multi-router/controllers/api_v1.js
index a301e3ee72d..f9dd06314bc 100644
--- a/examples/multi-router/controllers/api_v1.js
+++ b/examples/multi-router/controllers/api_v1.js
@@ -1,15 +1,15 @@
 'use strict'
 
-var express = require('../../..');
+const express = require('../../../')
 
-var apiv1 = express.Router();
+const apiv1 = express.Router()
 
-apiv1.get('/', function(req, res) {
-  res.send('Hello from APIv1 root route.');
-});
+apiv1.get('/', (req, res) => {
+  res.send('Hello from APIv1 root route.')
+})
 
-apiv1.get('/users', function(req, res) {
-  res.send('List of APIv1 users.');
-});
+apiv1.get('/users', (req, res) => {
+  res.send('List of APIv1 users.')
+})
 
-module.exports = apiv1;
+module.exports = apiv1
diff --git a/examples/multi-router/controllers/api_v2.js b/examples/multi-router/controllers/api_v2.js
index e997fb1f88c..bdb7699b8aa 100644
--- a/examples/multi-router/controllers/api_v2.js
+++ b/examples/multi-router/controllers/api_v2.js
@@ -1,15 +1,15 @@
 'use strict'
 
-var express = require('../../..');
+const express = require('../../../')
 
-var apiv2 = express.Router();
+const apiv2 = express.Router()
 
-apiv2.get('/', function(req, res) {
-  res.send('Hello from APIv2 root route.');
-});
+apiv2.get('/', (req, res) => {
+  res.send('Hello from APIv2 root route.')
+})
 
-apiv2.get('/users', function(req, res) {
-  res.send('List of APIv2 users.');
-});
+apiv2.get('/users', (req, res) => {
+  res.send('List of APIv2 users.')
+})
 
-module.exports = apiv2;
+module.exports = apiv2
diff --git a/examples/multi-router/index.js b/examples/multi-router/index.js
index dbfd2841262..44f264b3aa2 100644
--- a/examples/multi-router/index.js
+++ b/examples/multi-router/index.js
@@ -1,18 +1,18 @@
 'use strict'
 
-var express = require('../..');
+const express = require('../../')
 
-var app = module.exports = express();
+const app = module.exports = express()
 
-app.use('/api/v1', require('./controllers/api_v1'));
-app.use('/api/v2', require('./controllers/api_v2'));
+app.use('/api/v1', require('./controllers/api_v1'))
+app.use('/api/v2', require('./controllers/api_v2'))
 
-app.get('/', function(req, res) {
+app.get('/', (req, res) => {
   res.send('Hello from root route.')
-});
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/mvc/controllers/main/index.js b/examples/mvc/controllers/main/index.js
index 74cde191cd8..ad2956d00c2 100644
--- a/examples/mvc/controllers/main/index.js
+++ b/examples/mvc/controllers/main/index.js
@@ -1,5 +1,5 @@
 'use strict'
 
-exports.index = function(req, res){
-  res.redirect('/users');
-};
+exports.index = function (req, res) {
+  res.redirect('/users')
+}
diff --git a/examples/mvc/controllers/pet/index.js b/examples/mvc/controllers/pet/index.js
index 214160f9a46..48e9d92bf37 100644
--- a/examples/mvc/controllers/pet/index.js
+++ b/examples/mvc/controllers/pet/index.js
@@ -4,28 +4,28 @@
  * Module dependencies.
  */
 
-var db = require('../../db');
+const db = require('../../db')
 
-exports.engine = 'ejs';
+exports.engine = 'ejs'
 
-exports.before = function(req, res, next){
-  var pet = db.pets[req.params.pet_id];
-  if (!pet) return next('route');
-  req.pet = pet;
-  next();
-};
+exports.before = function (req, res, next) {
+  const pet = db.pets[req.params.pet_id]
+  if (!pet) return next('route')
+  req.pet = pet
+  next()
+}
 
-exports.show = function(req, res, next){
-  res.render('show', { pet: req.pet });
-};
+exports.show = function (req, res, next) {
+  res.render('show', { pet: req.pet })
+}
 
-exports.edit = function(req, res, next){
-  res.render('edit', { pet: req.pet });
-};
+exports.edit = function (req, res, next) {
+  res.render('edit', { pet: req.pet })
+}
 
-exports.update = function(req, res, next){
-  var body = req.body;
-  req.pet.name = body.pet.name;
-  res.message('Information updated!');
-  res.redirect('/pet/' + req.pet.id);
-};
+exports.update = function (req, res, next) {
+  const body = req.body
+  req.pet.name = body.pet.name
+  res.message('Information updated!')
+  res.redirect('/pet/' + req.pet.id)
+}
diff --git a/examples/mvc/controllers/user-pet/index.js b/examples/mvc/controllers/user-pet/index.js
index 42a29adebe7..cd90f4f23c1 100644
--- a/examples/mvc/controllers/user-pet/index.js
+++ b/examples/mvc/controllers/user-pet/index.js
@@ -4,19 +4,19 @@
  * Module dependencies.
  */
 
-var db = require('../../db');
+const db = require('../../db')
 
-exports.name = 'pet';
-exports.prefix = '/user/:user_id';
+exports.name = 'pet'
+exports.prefix = '/user/:user_id'
 
-exports.create = function(req, res, next){
-  var id = req.params.user_id;
-  var user = db.users[id];
-  var body = req.body;
-  if (!user) return next('route');
-  var pet = { name: body.pet.name };
-  pet.id = db.pets.push(pet) - 1;
-  user.pets.push(pet);
-  res.message('Added pet ' + body.pet.name);
-  res.redirect('/user/' + id);
-};
+exports.create = function (req, res, next) {
+  const id = req.params.user_id
+  const user = db.users[id]
+  const body = req.body
+  if (!user) return next('route')
+  const pet = { name: body.pet.name }
+  pet.id = db.pets.push(pet) - 1
+  user.pets.push(pet)
+  res.message('Added pet ' + body.pet.name)
+  res.redirect('/user/' + id)
+}
diff --git a/examples/mvc/controllers/user/index.js b/examples/mvc/controllers/user/index.js
index ec3ae4c8110..f9c6dc318bc 100644
--- a/examples/mvc/controllers/user/index.js
+++ b/examples/mvc/controllers/user/index.js
@@ -4,38 +4,38 @@
  * Module dependencies.
  */
 
-var db = require('../../db');
+const db = require('../../db')
 
-exports.engine = 'hbs';
+exports.engine = 'hbs'
 
-exports.before = function(req, res, next){
-  var id = req.params.user_id;
-  if (!id) return next();
+exports.before = function (req, res, next) {
+  const id = req.params.user_id
+  if (!id) return next()
   // pretend to query a database...
-  process.nextTick(function(){
-    req.user = db.users[id];
+  process.nextTick(() => {
+    req.user = db.users[id]
     // cant find that user
-    if (!req.user) return next('route');
+    if (!req.user) return next('route')
     // found it, move on to the routes
-    next();
-  });
-};
-
-exports.list = function(req, res, next){
-  res.render('list', { users: db.users });
-};
-
-exports.edit = function(req, res, next){
-  res.render('edit', { user: req.user });
-};
-
-exports.show = function(req, res, next){
-  res.render('show', { user: req.user });
-};
-
-exports.update = function(req, res, next){
-  var body = req.body;
-  req.user.name = body.user.name;
-  res.message('Information updated!');
-  res.redirect('/user/' + req.user.id);
-};
+    next()
+  })
+}
+
+exports.list = function (req, res, next) {
+  res.render('list', { users: db.users })
+}
+
+exports.edit = function (req, res, next) {
+  res.render('edit', { user: req.user })
+}
+
+exports.show = function (req, res, next) {
+  res.render('show', { user: req.user })
+}
+
+exports.update = function (req, res, next) {
+  const body = req.body
+  req.user.name = body.user.name
+  res.message('Information updated!')
+  res.redirect('/user/' + req.user.id)
+}
diff --git a/examples/mvc/db.js b/examples/mvc/db.js
index 94d1480f9b7..12101d50e9d 100644
--- a/examples/mvc/db.js
+++ b/examples/mvc/db.js
@@ -2,15 +2,15 @@
 
 // faux database
 
-var pets = exports.pets = [];
+const pets = exports.pets = []
 
-pets.push({ name: 'Tobi', id: 0 });
-pets.push({ name: 'Loki', id: 1 });
-pets.push({ name: 'Jane', id: 2 });
-pets.push({ name: 'Raul', id: 3 });
+pets.push({ name: 'Tobi', id: 0 })
+pets.push({ name: 'Loki', id: 1 })
+pets.push({ name: 'Jane', id: 2 })
+pets.push({ name: 'Raul', id: 3 })
 
-var users = exports.users = [];
+const users = exports.users = []
 
-users.push({ name: 'TJ', pets: [pets[0], pets[1], pets[2]], id: 0  });
-users.push({ name: 'Guillermo', pets: [pets[3]], id: 1 });
-users.push({ name: 'Nathan', pets: [], id: 2 });
+users.push({ name: 'TJ', pets: [pets[0], pets[1], pets[2]], id: 0 })
+users.push({ name: 'Guillermo', pets: [pets[3]], id: 1 })
+users.push({ name: 'Nathan', pets: [], id: 2 })
diff --git a/examples/mvc/index.js b/examples/mvc/index.js
index 1d8aa0e3c31..014fbc8e0dd 100644
--- a/examples/mvc/index.js
+++ b/examples/mvc/index.js
@@ -4,60 +4,60 @@
  * Module dependencies.
  */
 
-var express = require('../..');
-var logger = require('morgan');
-var path = require('node:path');
-var session = require('express-session');
-var methodOverride = require('method-override');
+const express = require('../../')
+const logger = require('morgan')
+const path = require('node:path')
+const session = require('express-session')
+const methodOverride = require('method-override')
 
-var app = module.exports = express();
+const app = module.exports = express()
 
 // set our default template engine to "ejs"
 // which prevents the need for using file extensions
-app.set('view engine', 'ejs');
+app.set('view engine', 'ejs')
 
 // set views for error and 404 pages
-app.set('views', path.join(__dirname, 'views'));
+app.set('views', path.join(__dirname, 'views'))
 
 // define a custom res.message() method
 // which stores messages in the session
-app.response.message = function(msg){
+app.response.message = function (msg) {
   // reference `req.session` via the `this.req` reference
-  var sess = this.req.session;
+  const sess = this.req.session
   // simply add the msg to an array for later
-  sess.messages = sess.messages || [];
-  sess.messages.push(msg);
-  return this;
-};
+  sess.messages = sess.messages || []
+  sess.messages.push(msg)
+  return this
+}
 
 // log
-if (!module.parent) app.use(logger('dev'));
+if (!module.parent) app.use(logger('dev'))
 
 // serve static files
-app.use(express.static(path.join(__dirname, 'public')));
+app.use(express.static(path.join(__dirname, 'public')))
 
 // session support
 app.use(session({
   resave: false, // don't save session if unmodified
   saveUninitialized: false, // don't create session until something stored
   secret: 'some secret here'
-}));
+}))
 
 // parse request bodies (req.body)
 app.use(express.urlencoded({ extended: true }))
 
 // allow overriding methods in query (?_method=put)
-app.use(methodOverride('_method'));
+app.use(methodOverride('_method'))
 
 // expose the "messages" local variable when views are rendered
-app.use(function(req, res, next){
-  var msgs = req.session.messages || [];
+app.use((req, res, next) => {
+  const msgs = req.session.messages || []
 
   // expose "messages" local variable
-  res.locals.messages = msgs;
+  res.locals.messages = msgs
 
   // expose "hasMessages"
-  res.locals.hasMessages = !! msgs.length;
+  res.locals.hasMessages = !!msgs.length
 
   /* This is equivalent:
    res.locals({
@@ -66,30 +66,30 @@ app.use(function(req, res, next){
    });
   */
 
-  next();
+  next()
   // empty or "flush" the messages so they
   // don't build up
-  req.session.messages = [];
-});
+  req.session.messages = []
+})
 
 // load controllers
-require('./lib/boot')(app, { verbose: !module.parent });
+require('./lib/boot')(app, { verbose: !module.parent })
 
-app.use(function(err, req, res, next){
+app.use((err, req, res, next) => {
   // log it
-  if (!module.parent) console.error(err.stack);
+  if (!module.parent) console.error(err.stack)
 
   // error page
-  res.status(500).render('5xx');
-});
+  res.status(500).render('5xx')
+})
 
 // assume 404 since no middleware responded
-app.use(function(req, res, next){
-  res.status(404).render('404', { url: req.originalUrl });
-});
+app.use((req, res, next) => {
+  res.status(404).render('404', { url: req.originalUrl })
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/mvc/lib/boot.js b/examples/mvc/lib/boot.js
index fc2ab0fad99..6932471f352 100644
--- a/examples/mvc/lib/boot.js
+++ b/examples/mvc/lib/boot.js
@@ -4,80 +4,81 @@
  * Module dependencies.
  */
 
-var express = require('../../..');
-var fs = require('node:fs');
-var path = require('node:path');
+const express = require('../../../')
+const fs = require('node:fs')
+const path = require('node:path')
 
-module.exports = function(parent, options){
-  var dir = path.join(__dirname, '..', 'controllers');
-  var verbose = options.verbose;
-  fs.readdirSync(dir).forEach(function(name){
-    var file = path.join(dir, name)
-    if (!fs.statSync(file).isDirectory()) return;
-    verbose && console.log('\n   %s:', name);
-    var obj = require(file);
-    var name = obj.name || name;
-    var prefix = obj.prefix || '';
-    var app = express();
-    var handler;
-    var method;
-    var url;
+module.exports = function (parent, options) {
+  const dir = path.join(__dirname, '..', 'controllers')
+  const verbose = options.verbose
+  fs.readdirSync(dir).forEach((dirname) => {
+    const subdir = path.join(dir, dirname)
+    if (!fs.statSync(subdir).isDirectory()) return
+    verbose && console.log('\n   %s:', dirname)
+    // eslint-disable-next-line global-require
+    const obj = require(subdir)
+    const name = obj.name || dirname
+    const prefix = obj.prefix || ''
+    const app = express()
+    let handler
+    let method
+    let url
 
     // allow specifying the view engine
-    if (obj.engine) app.set('view engine', obj.engine);
-    app.set('views', path.join(__dirname, '..', 'controllers', name, 'views'));
+    if (obj.engine) app.set('view engine', obj.engine)
+    app.set('views', path.join(__dirname, '..', 'controllers', name, 'views'))
 
     // generate routes based
     // on the exported methods
-    for (var key in obj) {
+    for (const key in obj) {
       // "reserved" exports
-      if (~['name', 'prefix', 'engine', 'before'].indexOf(key)) continue;
+      if (~['name', 'prefix', 'engine', 'before'].indexOf(key)) continue
       // route exports
       switch (key) {
         case 'show':
-          method = 'get';
-          url = '/' + name + '/:' + name + '_id';
-          break;
+          method = 'get'
+          url = '/' + name + '/:' + name + '_id'
+          break
         case 'list':
-          method = 'get';
-          url = '/' + name + 's';
-          break;
+          method = 'get'
+          url = '/' + name + 's'
+          break
         case 'edit':
-          method = 'get';
-          url = '/' + name + '/:' + name + '_id/edit';
-          break;
+          method = 'get'
+          url = '/' + name + '/:' + name + '_id/edit'
+          break
         case 'update':
-          method = 'put';
-          url = '/' + name + '/:' + name + '_id';
-          break;
+          method = 'put'
+          url = '/' + name + '/:' + name + '_id'
+          break
         case 'create':
-          method = 'post';
-          url = '/' + name;
-          break;
+          method = 'post'
+          url = '/' + name
+          break
         case 'index':
-          method = 'get';
-          url = '/';
-          break;
+          method = 'get'
+          url = '/'
+          break
         default:
           /* istanbul ignore next */
-          throw new Error('unrecognized route: ' + name + '.' + key);
+          throw new Error('unrecognized route: ' + name + '.' + key)
       }
 
       // setup
-      handler = obj[key];
-      url = prefix + url;
+      handler = obj[key]
+      url = prefix + url
 
       // before middleware support
       if (obj.before) {
-        app[method](url, obj.before, handler);
-        verbose && console.log('     %s %s -> before -> %s', method.toUpperCase(), url, key);
+        app[method](url, obj.before, handler)
+        verbose && console.log('     %s %s -> before -> %s', method.toUpperCase(), url, key)
       } else {
-        app[method](url, handler);
-        verbose && console.log('     %s %s -> %s', method.toUpperCase(), url, key);
+        app[method](url, handler)
+        verbose && console.log('     %s %s -> %s', method.toUpperCase(), url, key)
       }
     }
 
     // mount the app
-    parent.use(app);
-  });
-};
+    parent.use(app)
+  })
+}
diff --git a/examples/online/index.js b/examples/online/index.js
index 0b5fdffc86a..13e5b3dd071 100644
--- a/examples/online/index.js
+++ b/examples/online/index.js
@@ -11,51 +11,49 @@
  * Module dependencies.
  */
 
-var express = require('../..');
-var online = require('online');
-var redis = require('redis');
-var db = redis.createClient();
+const express = require('../../')
+let online = require('online')
+const redis = require('redis')
+const db = redis.createClient()
 
 // online
 
-online = online(db);
+online = online(db)
 
 // app
 
-var app = express();
+const app = express()
 
 // activity tracking, in this case using
 // the UA string, you would use req.user.id etc
 
-app.use(function(req, res, next){
+app.use((req, res, next) => {
   // fire-and-forget
-  online.add(req.headers['user-agent']);
-  next();
-});
+  online.add(req.headers['user-agent'])
+  next()
+})
 
 /**
  * List helper.
  */
 
-function list(ids) {
-  return '<ul>' + ids.map(function(id){
-    return '<li>' + id + '</li>';
-  }).join('') + '</ul>';
+function list (ids) {
+  return '<ul>' + ids.map((id) => '<li>' + id + '</li>').join('') + '</ul>'
 }
 
 /**
  * GET users online.
  */
 
-app.get('/', function(req, res, next){
-  online.last(5, function(err, ids){
-    if (err) return next(err);
-    res.send('<p>Users online: ' + ids.length + '</p>' + list(ids));
-  });
-});
+app.get('/', (req, res, next) => {
+  online.last(5, (err, ids) => {
+    if (err) return next(err)
+    res.send('<p>Users online: ' + ids.length + '</p>' + list(ids))
+  })
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/params/index.js b/examples/params/index.js
index 11eef51a592..d565ac5e373 100644
--- a/examples/params/index.js
+++ b/examples/params/index.js
@@ -4,71 +4,71 @@
  * Module dependencies.
  */
 
-var createError = require('http-errors')
-var express = require('../../');
-var app = module.exports = express();
+const createError = require('http-errors')
+const express = require('../../')
+const app = module.exports = express()
 
 // Faux database
 
-var users = [
-  { name: 'tj' }
-  , { name: 'tobi' }
-  , { name: 'loki' }
-  , { name: 'jane' }
-  , { name: 'bandit' }
-];
+const users = [
+  { name: 'tj' },
+  { name: 'tobi' },
+  { name: 'loki' },
+  { name: 'jane' },
+  { name: 'bandit' }
+]
 
 // Convert :to and :from to integers
 
-app.param(['to', 'from'], function(req, res, next, num, name){
-  req.params[name] = parseInt(num, 10);
-  if( isNaN(req.params[name]) ){
-    next(createError(400, 'failed to parseInt '+num));
+app.param(['to', 'from'], (req, res, next, num, name) => {
+  req.params[name] = parseInt(num, 10)
+  if (isNaN(req.params[name])) {
+    next(createError(400, 'failed to parseInt ' + num))
   } else {
-    next();
+    next()
   }
-});
+})
 
 // Load user by id
 
-app.param('user', function(req, res, next, id){
+app.param('user', (req, res, next, id) => {
   req.user = users[id]
   if (req.user) {
-    next();
+    next()
   } else {
-    next(createError(404, 'failed to find user'));
+    next(createError(404, 'failed to find user'))
   }
-});
+})
 
 /**
  * GET index.
  */
 
-app.get('/', function(req, res){
-  res.send('Visit /user/0 or /users/0-2');
-});
+app.get('/', (req, res) => {
+  res.send('Visit /user/0 or /users/0-2')
+})
 
 /**
  * GET :user.
  */
 
-app.get('/user/:user', function (req, res) {
-  res.send('user ' + req.user.name);
-});
+app.get('/user/:user', (req, res) => {
+  res.send('user ' + req.user.name)
+})
 
 /**
  * GET users :from - :to.
  */
 
-app.get('/users/:from-:to', function (req, res) {
-  var from = req.params.from;
-  var to = req.params.to;
-  var names = users.map(function(user){ return user.name; });
-  res.send('users ' + names.slice(from, to + 1).join(', '));
-});
+app.get('/users/:from-:to', (req, res) => {
+  const from = req.params.from
+  const to = req.params.to
+  const names = users.map((user) => user.name)
+  res.send('users ' + names.slice(from, to + 1).join(', '))
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/resource/index.js b/examples/resource/index.js
index 627ab24c5a2..bea4411843c 100644
--- a/examples/resource/index.js
+++ b/examples/resource/index.js
@@ -4,68 +4,65 @@
  * Module dependencies.
  */
 
-var express = require('../../');
+const express = require('../../')
 
-var app = module.exports = express();
+const app = module.exports = express()
 
 // Ad-hoc example resource method
 
-app.resource = function(path, obj) {
-  this.get(path, obj.index);
-  this.get(path + '/:a..:b{.:format}', function(req, res){
-    var a = parseInt(req.params.a, 10);
-    var b = parseInt(req.params.b, 10);
-    var format = req.params.format;
-    obj.range(req, res, a, b, format);
-  });
-  this.get(path + '/:id', obj.show);
-  this.delete(path + '/:id', function(req, res){
-    var id = parseInt(req.params.id, 10);
-    obj.destroy(req, res, id);
-  });
-};
+app.resource = function (path, obj) {
+  this.get(path, obj.index)
+  this.get(path + '/:a..:b{.:format}', (req, res) => {
+    const a = parseInt(req.params.a, 10)
+    const b = parseInt(req.params.b, 10)
+    const format = req.params.format
+    obj.range(req, res, a, b, format)
+  })
+  this.get(path + '/:id', obj.show)
+  this.delete(path + '/:id', (req, res) => {
+    const id = parseInt(req.params.id, 10)
+    obj.destroy(req, res, id)
+  })
+}
 
 // Fake records
 
-var users = [
-  { name: 'tj' }
-  , { name: 'ciaran' }
-  , { name: 'aaron' }
-  , { name: 'guillermo' }
-  , { name: 'simon' }
-  , { name: 'tobi' }
-];
+const users = [
+  { name: 'tj' },
+  { name: 'ciaran' },
+  { name: 'aaron' },
+  { name: 'guillermo' },
+  { name: 'simon' },
+  { name: 'tobi' }
+]
 
 // Fake controller.
 
-var User = {
-  index: function(req, res){
-    res.send(users);
+const User = {
+  index: function (req, res) {
+    res.send(users)
   },
-  show: function(req, res){
-    res.send(users[req.params.id] || { error: 'Cannot find user' });
+  show: function (req, res) {
+    res.send(users[req.params.id] || { error: 'Cannot find user' })
   },
-  destroy: function(req, res, id){
-    var destroyed = id in users;
-    delete users[id];
-    res.send(destroyed ? 'destroyed' : 'Cannot find user');
+  destroy: function (req, res, id) {
+    const destroyed = id in users
+    delete users[id]
+    res.send(destroyed ? 'destroyed' : 'Cannot find user')
   },
-  range: function(req, res, a, b, format){
-    var range = users.slice(a, b + 1);
+  range: function (req, res, a, b, format) {
+    const range = users.slice(a, b + 1)
     switch (format) {
       case 'json':
-        res.send(range);
-        break;
+        res.send(range)
+        break
       case 'html':
       default:
-        var html = '<ul>' + range.map(function(user){
-          return '<li>' + user.name + '</li>';
-        }).join('\n') + '</ul>';
-        res.send(html);
-        break;
+        res.send('<ul>' + range.map(user => '<li>' + user.name + '</li>').join('\n') + '</ul>')
+        break
     }
   }
-};
+}
 
 // curl http://localhost:3000/users     -- responds with all users
 // curl http://localhost:3000/users/1   -- responds with user 1
@@ -73,23 +70,23 @@ var User = {
 // curl http://localhost:3000/users/1..3 -- responds with several users
 // curl -X DELETE http://localhost:3000/users/1  -- deletes the user
 
-app.resource('/users', User);
+app.resource('/users', User)
 
-app.get('/', function(req, res){
+app.get('/', (req, res) => {
   res.send([
-    '<h1>Examples:</h1> <ul>'
-    , '<li>GET /users</li>'
-    , '<li>GET /users/1</li>'
-    , '<li>GET /users/3</li>'
-    , '<li>GET /users/1..3</li>'
-    , '<li>GET /users/1..3.json</li>'
-    , '<li>DELETE /users/4</li>'
-    , '</ul>'
-  ].join('\n'));
-});
+    '<h1>Examples:</h1> <ul>',
+    '<li>GET /users</li>',
+    '<li>GET /users/1</li>',
+    '<li>GET /users/3</li>',
+    '<li>GET /users/1..3</li>',
+    '<li>GET /users/1..3.json</li>',
+    '<li>DELETE /users/4</li>',
+    '</ul>'
+  ].join('\n'))
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/route-map/index.js b/examples/route-map/index.js
index 2bc28bd4b26..71954772f0e 100644
--- a/examples/route-map/index.js
+++ b/examples/route-map/index.js
@@ -4,53 +4,53 @@
  * Module dependencies.
  */
 
-var escapeHtml = require('escape-html')
-var express = require('../../lib/express');
+const escapeHtml = require('escape-html')
+const express = require('../../')
 
-var verbose = process.env.NODE_ENV !== 'test'
+const verbose = process.env.NODE_ENV !== 'test'
 
-var app = module.exports = express();
+const app = module.exports = express()
 
-app.map = function(a, route){
-  route = route || '';
-  for (var key in a) {
+app.map = function (a, route) {
+  route = route || ''
+  for (const key in a) {
     switch (typeof a[key]) {
       // { '/path': { ... }}
       case 'object':
-        app.map(a[key], route + key);
-        break;
+        app.map(a[key], route + key)
+        break
       // get: function(){ ... }
       case 'function':
-        if (verbose) console.log('%s %s', key, route);
-        app[key](route, a[key]);
-        break;
+        if (verbose) console.log('%s %s', key, route)
+        app[key](route, a[key])
+        break
     }
   }
-};
+}
 
-var users = {
-  list: function(req, res){
-    res.send('user list');
+const users = {
+  list: function (req, res) {
+    res.send('user list')
   },
 
-  get: function(req, res){
-    res.send('user ' +  escapeHtml(req.params.uid))
+  get: function (req, res) {
+    res.send('user ' + escapeHtml(req.params.uid))
   },
 
-  delete: function(req, res){
-    res.send('delete users');
+  delete: function (req, res) {
+    res.send('delete users')
   }
-};
+}
 
-var pets = {
-  list: function(req, res){
+const pets = {
+  list: function (req, res) {
     res.send('user ' + escapeHtml(req.params.uid) + '\'s pets')
   },
 
-  delete: function(req, res){
+  delete: function (req, res) {
     res.send('delete ' + escapeHtml(req.params.uid) + '\'s pet ' + escapeHtml(req.params.pid))
   }
-};
+}
 
 app.map({
   '/users': {
@@ -66,10 +66,10 @@ app.map({
       }
     }
   }
-});
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/route-middleware/index.js b/examples/route-middleware/index.js
index 44ec13a95b8..d738f33e417 100644
--- a/examples/route-middleware/index.js
+++ b/examples/route-middleware/index.js
@@ -4,9 +4,9 @@
  * Module dependencies.
  */
 
-var express = require('../../lib/express');
+const express = require('../../')
 
-var app = express();
+const app = express()
 
 // Example requests:
 //     curl http://localhost:3000/user/0
@@ -16,43 +16,43 @@ var app = express();
 //     curl -X DELETE http://localhost:3000/user/0 (unauthorized since you are not an admin)
 
 // Dummy users
-var users = [
-  { id: 0, name: 'tj', email: 'tj@vision-media.ca', role: 'member' }
-  , { id: 1, name: 'ciaran', email: 'ciaranj@gmail.com', role: 'member' }
-  , { id: 2, name: 'aaron', email: 'aaron.heckmann+github@gmail.com', role: 'admin' }
-];
+const users = [
+  { id: 0, name: 'tj', email: 'tj@vision-media.ca', role: 'member' },
+  { id: 1, name: 'ciaran', email: 'ciaranj@gmail.com', role: 'member' },
+  { id: 2, name: 'aaron', email: 'aaron.heckmann+github@gmail.com', role: 'admin' }
+]
 
-function loadUser(req, res, next) {
+function loadUser (req, res, next) {
   // You would fetch your user from the db
-  var user = users[req.params.id];
+  const user = users[req.params.id]
   if (user) {
-    req.user = user;
-    next();
+    req.user = user
+    next()
   } else {
-    next(new Error('Failed to load user ' + req.params.id));
+    next(new Error('Failed to load user ' + req.params.id))
   }
 }
 
-function andRestrictToSelf(req, res, next) {
+function andRestrictToSelf (req, res, next) {
   // If our authenticated user is the user we are viewing
   // then everything is fine :)
   if (req.authenticatedUser.id === req.user.id) {
-    next();
+    next()
   } else {
     // You may want to implement specific exceptions
     // such as UnauthorizedError or similar so that you
     // can handle these can be special-cased in an error handler
     // (view ./examples/pages for this)
-    next(new Error('Unauthorized'));
+    next(new Error('Unauthorized'))
   }
 }
 
-function andRestrictTo(role) {
-  return function(req, res, next) {
+function andRestrictTo (role) {
+  return function (req, res, next) {
     if (req.authenticatedUser.role === role) {
-      next();
+      next()
     } else {
-      next(new Error('Unauthorized'));
+      next(new Error('Unauthorized'))
     }
   }
 }
@@ -62,29 +62,29 @@ function andRestrictTo(role) {
 // but this illustrates how an authenticated user
 // may interact with middleware
 
-app.use(function(req, res, next){
-  req.authenticatedUser = users[0];
-  next();
-});
+app.use((req, res, next) => {
+  req.authenticatedUser = users[0]
+  next()
+})
 
-app.get('/', function(req, res){
-  res.redirect('/user/0');
-});
+app.get('/', (req, res) => {
+  res.redirect('/user/0')
+})
 
-app.get('/user/:id', loadUser, function(req, res){
-  res.send('Viewing user ' + req.user.name);
-});
+app.get('/user/:id', loadUser, (req, res) => {
+  res.send('Viewing user ' + req.user.name)
+})
 
-app.get('/user/:id/edit', loadUser, andRestrictToSelf, function(req, res){
-  res.send('Editing user ' + req.user.name);
-});
+app.get('/user/:id/edit', loadUser, andRestrictToSelf, (req, res) => {
+  res.send('Editing user ' + req.user.name)
+})
 
-app.delete('/user/:id', loadUser, andRestrictTo('admin'), function(req, res){
-  res.send('Deleted user ' + req.user.name);
-});
+app.delete('/user/:id', loadUser, andRestrictTo('admin'), (req, res) => {
+  res.send('Deleted user ' + req.user.name)
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/route-separation/index.js b/examples/route-separation/index.js
index 0a29c9421a6..148d617cc1f 100644
--- a/examples/route-separation/index.js
+++ b/examples/route-separation/index.js
@@ -4,52 +4,52 @@
  * Module dependencies.
  */
 
-var express = require('../..');
-var path = require('node:path');
-var app = express();
-var logger = require('morgan');
-var cookieParser = require('cookie-parser');
-var methodOverride = require('method-override');
-var site = require('./site');
-var post = require('./post');
-var user = require('./user');
-
-module.exports = app;
+const express = require('../../')
+const path = require('node:path')
+const app = express()
+const logger = require('morgan')
+const cookieParser = require('cookie-parser')
+const methodOverride = require('method-override')
+const site = require('./site')
+const post = require('./post')
+const user = require('./user')
+
+module.exports = app
 
 // Config
 
-app.set('view engine', 'ejs');
-app.set('views', path.join(__dirname, 'views'));
+app.set('view engine', 'ejs')
+app.set('views', path.join(__dirname, 'views'))
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.use(logger('dev'));
+  app.use(logger('dev'))
 }
 
-app.use(methodOverride('_method'));
-app.use(cookieParser());
+app.use(methodOverride('_method'))
+app.use(cookieParser())
 app.use(express.urlencoded({ extended: true }))
-app.use(express.static(path.join(__dirname, 'public')));
+app.use(express.static(path.join(__dirname, 'public')))
 
 // General
 
-app.get('/', site.index);
+app.get('/', site.index)
 
 // User
 
-app.get('/users', user.list);
-app.all('/user/:id{/:op}', user.load);
-app.get('/user/:id', user.view);
-app.get('/user/:id/view', user.view);
-app.get('/user/:id/edit', user.edit);
-app.put('/user/:id/edit', user.update);
+app.get('/users', user.list)
+app.all('/user/:id{/:op}', user.load)
+app.get('/user/:id', user.view)
+app.get('/user/:id/view', user.view)
+app.get('/user/:id/edit', user.edit)
+app.put('/user/:id/edit', user.update)
 
 // Posts
 
-app.get('/posts', post.list);
+app.get('/posts', post.list)
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/route-separation/post.js b/examples/route-separation/post.js
index 3a8e3a2d225..19cd89137e2 100644
--- a/examples/route-separation/post.js
+++ b/examples/route-separation/post.js
@@ -2,12 +2,12 @@
 
 // Fake posts database
 
-var posts = [
+const posts = [
   { title: 'Foo', body: 'some foo bar' },
   { title: 'Foo bar', body: 'more foo bar' },
   { title: 'Foo bar baz', body: 'more foo bar baz' }
-];
+]
 
-exports.list = function(req, res){
-  res.render('posts', { title: 'Posts', posts: posts });
-};
+exports.list = function (req, res) {
+  res.render('posts', { title: 'Posts', posts })
+}
diff --git a/examples/route-separation/site.js b/examples/route-separation/site.js
index aee36d1bd72..ef4e8866645 100644
--- a/examples/route-separation/site.js
+++ b/examples/route-separation/site.js
@@ -1,5 +1,5 @@
 'use strict'
 
-exports.index = function(req, res){
-  res.render('index', { title: 'Route Separation Example' });
-};
+exports.index = function (req, res) {
+  res.render('index', { title: 'Route Separation Example' })
+}
diff --git a/examples/route-separation/user.js b/examples/route-separation/user.js
index bc6fbd7baf3..28b46c5e6cb 100644
--- a/examples/route-separation/user.js
+++ b/examples/route-separation/user.js
@@ -2,46 +2,46 @@
 
 // Fake user database
 
-var users = [
+const users = [
   { name: 'TJ', email: 'tj@vision-media.ca' },
   { name: 'Tobi', email: 'tobi@vision-media.ca' }
-];
+]
 
-exports.list = function(req, res){
-  res.render('users', { title: 'Users', users: users });
-};
+exports.list = function (req, res) {
+  res.render('users', { title: 'Users', users })
+}
 
-exports.load = function(req, res, next){
-  var id = req.params.id;
-  req.user = users[id];
+exports.load = function (req, res, next) {
+  const id = req.params.id
+  req.user = users[id]
   if (req.user) {
-    next();
+    next()
   } else {
-    var err = new Error('cannot find user ' + id);
-    err.status = 404;
-    next(err);
+    const err = new Error('cannot find user ' + id)
+    err.status = 404
+    next(err)
   }
-};
+}
 
-exports.view = function(req, res){
+exports.view = function (req, res) {
   res.render('users/view', {
     title: 'Viewing user ' + req.user.name,
     user: req.user
-  });
-};
+  })
+}
 
-exports.edit = function(req, res){
+exports.edit = function (req, res) {
   res.render('users/edit', {
     title: 'Editing user ' + req.user.name,
     user: req.user
-  });
-};
+  })
+}
 
-exports.update = function(req, res){
+exports.update = function (req, res) {
   // Normally you would handle all kinds of
   // validation and save back to the db
-  var user = req.body.user;
-  req.user.name = user.name;
-  req.user.email = user.email;
-  res.redirect(req.get('Referrer') || '/');
-};
+  const user = req.body.user
+  req.user.name = user.name
+  req.user.email = user.email
+  res.redirect(req.get('Referrer') || '/')
+}
diff --git a/examples/search/index.js b/examples/search/index.js
index 951e0d440a6..3a9ca142500 100644
--- a/examples/search/index.js
+++ b/examples/search/index.js
@@ -11,37 +11,37 @@
  * Module dependencies.
  */
 
-var express = require('../..');
-var path = require('node:path');
-var redis = require('redis');
+const express = require('../../')
+const path = require('node:path')
+const redis = require('redis')
 
-var db = redis.createClient();
+const db = redis.createClient()
 
 // npm install redis
 
-var app = express();
+const app = express()
 
-app.use(express.static(path.join(__dirname, 'public')));
+app.use(express.static(path.join(__dirname, 'public')))
 
 // populate search
 
-db.sadd('ferret', 'tobi');
-db.sadd('ferret', 'loki');
-db.sadd('ferret', 'jane');
-db.sadd('cat', 'manny');
-db.sadd('cat', 'luna');
+db.sadd('ferret', 'tobi')
+db.sadd('ferret', 'loki')
+db.sadd('ferret', 'jane')
+db.sadd('cat', 'manny')
+db.sadd('cat', 'luna')
 
 /**
  * GET search for :query.
  */
 
-app.get('/search/:query?', function(req, res, next){
-  var query = req.params.query;
-  db.smembers(query, function(err, vals){
-    if (err) return next(err);
-    res.send(vals);
-  });
-});
+app.get('/search/:query?', (req, res, next) => {
+  const query = req.params.query
+  db.smembers(query, (err, vals) => {
+    if (err) return next(err)
+    res.send(vals)
+  })
+})
 
 /**
  * GET client javascript. Here we use sendFile()
@@ -50,12 +50,12 @@ app.get('/search/:query?', function(req, res, next){
  * template.
  */
 
-app.get('/client.js', function(req, res){
-  res.sendFile(path.join(__dirname, 'client.js'));
-});
+app.get('/client.js', (req, res) => {
+  res.sendFile(path.join(__dirname, 'client.js'))
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/search/public/client.js b/examples/search/public/client.js
index cd43faf71e0..4b73c0e1b95 100644
--- a/examples/search/public/client.js
+++ b/examples/search/public/client.js
@@ -1,15 +1,17 @@
 'use strict'
 
-var search = document.querySelector('[type=search]');
-var code = document.querySelector('pre');
+const search = document.querySelector('[type=search]')
+const code = document.querySelector('pre')
 
-search.addEventListener('keyup', function(){
-  var xhr = new XMLHttpRequest;
-  xhr.open('GET', '/search/' + search.value, true);
-  xhr.onreadystatechange = function(){
+/* global XMLHttpRequest */
+
+search.addEventListener('keyup', () => {
+  const xhr = new XMLHttpRequest()
+  xhr.open('GET', '/search/' + search.value, true)
+  xhr.onreadystatechange = function () {
     if (xhr.readyState === 4) {
-      code.textContent = xhr.responseText;
+      code.textContent = xhr.responseText
     }
-  };
-  xhr.send();
-}, false);
+  }
+  xhr.send()
+}, false)
diff --git a/examples/session/index.js b/examples/session/index.js
index 2bb2b109c82..4d0a25c4ba5 100644
--- a/examples/session/index.js
+++ b/examples/session/index.js
@@ -7,31 +7,31 @@
 // $ npm install redis
 // $ redis-server
 
-var express = require('../..');
-var session = require('express-session');
+const express = require('../../')
+const session = require('express-session')
 
-var app = express();
+const app = express()
 
 // Populates req.session
 app.use(session({
   resave: false, // don't save session if unmodified
   saveUninitialized: false, // don't create session until something stored
   secret: 'keyboard cat'
-}));
+}))
 
-app.get('/', function(req, res){
-  var body = '';
+app.get('/', (req, res) => {
+  let body = ''
   if (req.session.views) {
-    ++req.session.views;
+    ++req.session.views
   } else {
-    req.session.views = 1;
-    body += '<p>First time visiting? view this page in several browsers :)</p>';
+    req.session.views = 1
+    body += '<p>First time visiting? view this page in several browsers :)</p>'
   }
-  res.send(body + '<p>viewed <strong>' + req.session.views + '</strong> times.</p>');
-});
+  res.send(body + '<p>viewed <strong>' + req.session.views + '</strong> times.</p>')
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/session/redis.js b/examples/session/redis.js
index bbbdc7fd3e5..f967971db03 100644
--- a/examples/session/redis.js
+++ b/examples/session/redis.js
@@ -4,36 +4,36 @@
  * Module dependencies.
  */
 
-var express = require('../..');
-var logger = require('morgan');
-var session = require('express-session');
+const express = require('../../')
+const logger = require('morgan')
+const session = require('express-session')
 
 // pass the express to the connect redis module
 // allowing it to inherit from session.Store
-var RedisStore = require('connect-redis')(session);
+const RedisStore = require('connect-redis')(session)
 
-var app = express();
+const app = express()
 
-app.use(logger('dev'));
+app.use(logger('dev'))
 
 // Populates req.session
 app.use(session({
   resave: false, // don't save session if unmodified
   saveUninitialized: false, // don't create session until something stored
   secret: 'keyboard cat',
-  store: new RedisStore
-}));
+  store: new RedisStore()
+}))
 
-app.get('/', function(req, res){
-  var body = '';
+app.get('/', (req, res) => {
+  let body = ''
   if (req.session.views) {
-    ++req.session.views;
+    ++req.session.views
   } else {
-    req.session.views = 1;
-    body += '<p>First time visiting? view this page in several browsers :)</p>';
+    req.session.views = 1
+    body += '<p>First time visiting? view this page in several browsers :)</p>'
   }
-  res.send(body + '<p>viewed <strong>' + req.session.views + '</strong> times.</p>');
-});
+  res.send(body + '<p>viewed <strong>' + req.session.views + '</strong> times.</p>')
+})
 
-app.listen(3000);
-console.log('Express app started on port 3000');
+app.listen(3000)
+console.log('Express app started on port 3000')
diff --git a/examples/static-files/index.js b/examples/static-files/index.js
index b7c697a2f9f..89540176bde 100644
--- a/examples/static-files/index.js
+++ b/examples/static-files/index.js
@@ -4,13 +4,13 @@
  * Module dependencies.
  */
 
-var express = require('../..');
-var logger = require('morgan');
-var path = require('node:path');
-var app = express();
+const express = require('../../')
+const logger = require('morgan')
+const path = require('node:path')
+const app = express()
 
 // log requests
-app.use(logger('dev'));
+app.use(logger('dev'))
 
 // express on its own has no notion
 // of a "file". The express.static()
@@ -19,7 +19,7 @@ app.use(logger('dev'));
 // that you pass it. In this case "GET /js/app.js"
 // will look for "./public/js/app.js".
 
-app.use(express.static(path.join(__dirname, 'public')));
+app.use(express.static(path.join(__dirname, 'public')))
 
 // if you wanted to "prefix" you may use
 // the mounting feature of Connect, for example
@@ -27,17 +27,17 @@ app.use(express.static(path.join(__dirname, 'public')));
 // The mount-path "/static" is simply removed before
 // passing control to the express.static() middleware,
 // thus it serves the file correctly by ignoring "/static"
-app.use('/static', express.static(path.join(__dirname, 'public')));
+app.use('/static', express.static(path.join(__dirname, 'public')))
 
 // if for some reason you want to serve files from
 // several directories, you can use express.static()
 // multiple times! Here we're passing "./public/css",
 // this will allow "GET /style.css" instead of "GET /css/style.css":
-app.use(express.static(path.join(__dirname, 'public', 'css')));
-
-app.listen(3000);
-console.log('listening on port 3000');
-console.log('try:');
-console.log('  GET /hello.txt');
-console.log('  GET /js/app.js');
-console.log('  GET /css/style.css');
+app.use(express.static(path.join(__dirname, 'public', 'css')))
+
+app.listen(3000)
+console.log('listening on port 3000')
+console.log('try:')
+console.log('  GET /hello.txt')
+console.log('  GET /js/app.js')
+console.log('  GET /css/style.css')
diff --git a/examples/vhost/index.js b/examples/vhost/index.js
index a9499356b42..d63400d953b 100644
--- a/examples/vhost/index.js
+++ b/examples/vhost/index.js
@@ -4,9 +4,9 @@
  * Module dependencies.
  */
 
-var express = require('../..');
-var logger = require('morgan');
-var vhost = require('vhost');
+const express = require('../../')
+const logger = require('morgan')
+const vhost = require('vhost')
 
 /*
 edit /etc/hosts:
@@ -18,36 +18,36 @@ edit /etc/hosts:
 
 // Main server app
 
-var main = express();
+const main = express()
 
-if (!module.parent) main.use(logger('dev'));
+if (!module.parent) main.use(logger('dev'))
 
-main.get('/', function(req, res){
-  res.send('Hello from main app!');
-});
+main.get('/', (req, res) => {
+  res.send('Hello from main app!')
+})
 
-main.get('/:sub', function(req, res){
-  res.send('requested ' + req.params.sub);
-});
+main.get('/:sub', (req, res) => {
+  res.send('requested ' + req.params.sub)
+})
 
 // Redirect app
 
-var redirect = express();
+const redirect = express()
 
-redirect.use(function(req, res){
-  if (!module.parent) console.log(req.vhost);
-  res.redirect('http://example.com:3000/' + req.vhost[0]);
-});
+redirect.use((req, res) => {
+  if (!module.parent) console.log(req.vhost)
+  res.redirect('http://example.com:3000/' + req.vhost[0])
+})
 
 // Vhost app
 
-var app = module.exports = express();
+const app = module.exports = express()
 
-app.use(vhost('*.example.com', redirect)); // Serves all subdomains via Redirect app
-app.use(vhost('example.com', main)); // Serves top level domain via Main server app
+app.use(vhost('*.example.com', redirect)) // Serves all subdomains via Redirect app
+app.use(vhost('example.com', main)) // Serves top level domain via Main server app
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/view-constructor/github-view.js b/examples/view-constructor/github-view.js
index eabfb2d0c18..58bb92adfdf 100644
--- a/examples/view-constructor/github-view.js
+++ b/examples/view-constructor/github-view.js
@@ -4,15 +4,15 @@
  * Module dependencies.
  */
 
-var https = require('node:https');
-var path = require('node:path');
-var extname = path.extname;
+const https = require('node:https')
+const path = require('node:path')
+const extname = path.extname
 
 /**
  * Expose `GithubView`.
  */
 
-module.exports = GithubView;
+module.exports = GithubView
 
 /**
  * Custom view that fetches and renders
@@ -20,34 +20,34 @@ module.exports = GithubView;
  * render templates from a database etc.
  */
 
-function GithubView(name, options){
-  this.name = name;
-  options = options || {};
-  this.engine = options.engines[extname(name)];
+function GithubView (name, options) {
+  this.name = name
+  options = options || {}
+  this.engine = options.engines[extname(name)]
   // "root" is the app.set('views') setting, however
   // in your own implementation you could ignore this
-  this.path = '/' + options.root + '/master/' + name;
+  this.path = '/' + options.root + '/master/' + name
 }
 
 /**
  * Render the view.
  */
 
-GithubView.prototype.render = function(options, fn){
-  var self = this;
-  var opts = {
+GithubView.prototype.render = function (options, fn) {
+  const self = this
+  const opts = {
     host: 'raw.githubusercontent.com',
     port: 443,
     path: this.path,
     method: 'GET'
-  };
-
-  https.request(opts, function(res) {
-    var buf = '';
-    res.setEncoding('utf8');
-    res.on('data', function(str){ buf += str });
-    res.on('end', function(){
-      self.engine(buf, options, fn);
-    });
-  }).end();
-};
+  }
+
+  https.request(opts, (res) => {
+    let buf = ''
+    res.setEncoding('utf8')
+    res.on('data', (str) => { buf += str })
+    res.on('end', () => {
+      self.engine(buf, options, fn)
+    })
+  }).end()
+}
diff --git a/examples/view-constructor/index.js b/examples/view-constructor/index.js
index 3d673670e31..bde51f89b1a 100644
--- a/examples/view-constructor/index.js
+++ b/examples/view-constructor/index.js
@@ -4,45 +4,43 @@
  * Module dependencies.
  */
 
-var express = require('../../');
-var GithubView = require('./github-view');
-var md = require('marked').parse;
+const express = require('../../')
+const GithubView = require('./github-view')
+const md = require('marked').parse
 
-var app = module.exports = express();
+const app = module.exports = express()
 
 // register .md as an engine in express view system
-app.engine('md', function(str, options, fn){
+app.engine('md', (str, options, fn) => {
   try {
-    var html = md(str);
-    html = html.replace(/\{([^}]+)\}/g, function(_, name){
-      return options[name] || '';
-    });
-    fn(null, html);
-  } catch(err) {
-    fn(err);
+    let html = md(str)
+    html = html.replace(/\{([^}]+)\}/g, (_, name) => options[name] || '')
+    fn(null, html)
+  } catch (err) {
+    fn(err)
   }
-});
+})
 
 // pointing to a particular github repo to load files from it
-app.set('views', 'expressjs/express');
+app.set('views', 'expressjs/express')
 
 // register a new view constructor
-app.set('view', GithubView);
+app.set('view', GithubView)
 
-app.get('/', function(req, res){
+app.get('/', (req, res) => {
   // rendering a view relative to the repo.
   // app.locals, res.locals, and locals passed
   // work like they normally would
-  res.render('examples/markdown/views/index.md', { title: 'Example' });
-});
+  res.render('examples/markdown/views/index.md', { title: 'Example' })
+})
 
-app.get('/Readme.md', function(req, res){
+app.get('/Readme.md', (req, res) => {
   // rendering a view from https://github.com/expressjs/express/blob/master/Readme.md
-  res.render('Readme.md');
-});
+  res.render('Readme.md')
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/view-locals/index.js b/examples/view-locals/index.js
index e6355602d4e..f48fdbf257a 100644
--- a/examples/view-locals/index.js
+++ b/examples/view-locals/index.js
@@ -4,17 +4,17 @@
  * Module dependencies.
  */
 
-var express = require('../..');
-var path = require('node:path');
-var User = require('./user');
-var app = express();
+const express = require('../../')
+const path = require('node:path')
+const User = require('./user')
+const app = express()
 
-app.set('views', path.join(__dirname, 'views'));
-app.set('view engine', 'ejs');
+app.set('views', path.join(__dirname, 'views'))
+app.set('view engine', 'ejs')
 
 // filter ferrets only
 
-function ferrets(user) {
+function ferrets (user) {
   return user.species === 'ferret'
 }
 
@@ -23,54 +23,48 @@ function ferrets(user) {
 // in order to expose the "count"
 // and "users" locals
 
-app.get('/', function(req, res, next){
-  User.count(function(err, count){
-    if (err) return next(err);
-    User.all(function(err, users){
-      if (err) return next(err);
+app.get('/', (req, res, next) => {
+  User.count((err, count) => {
+    if (err) return next(err)
+    User.all((err, users) => {
+      if (err) return next(err)
       res.render('index', {
         title: 'Users',
-        count: count,
+        count,
         users: users.filter(ferrets)
-      });
+      })
     })
   })
-});
-
-
-
+})
 
 // this approach is cleaner,
 // less nesting and we have
 // the variables available
 // on the request object
 
-function count(req, res, next) {
-  User.count(function(err, count){
-    if (err) return next(err);
-    req.count = count;
-    next();
+function count (req, res, next) {
+  User.count((err, count) => {
+    if (err) return next(err)
+    req.count = count
+    next()
   })
 }
 
-function users(req, res, next) {
-  User.all(function(err, users){
-    if (err) return next(err);
-    req.users = users;
-    next();
+function users (req, res, next) {
+  User.all((err, users) => {
+    if (err) return next(err)
+    req.users = users
+    next()
   })
 }
 
-app.get('/middleware', count, users, function (req, res) {
+app.get('/middleware', count, users, (req, res) => {
   res.render('index', {
     title: 'Users',
     count: req.count,
     users: req.users.filter(ferrets)
-  });
-});
-
-
-
+  })
+})
 
 // this approach is much like the last
 // however we're explicitly exposing
@@ -83,29 +77,29 @@ app.get('/middleware', count, users, function (req, res) {
 // so in that sense the previous example
 // is more flexible with `req.users`.
 
-function count2(req, res, next) {
-  User.count(function(err, count){
-    if (err) return next(err);
-    res.locals.count = count;
-    next();
+function count2 (req, res, next) {
+  User.count((err, count) => {
+    if (err) return next(err)
+    res.locals.count = count
+    next()
   })
 }
 
-function users2(req, res, next) {
-  User.all(function(err, users){
-    if (err) return next(err);
-    res.locals.users = users.filter(ferrets);
-    next();
+function users2 (req, res, next) {
+  User.all((err, users) => {
+    if (err) return next(err)
+    res.locals.users = users.filter(ferrets)
+    next()
   })
 }
 
-app.get('/middleware-locals', count2, users2, function (req, res) {
+app.get('/middleware-locals', count2, users2, (req, res) => {
   // you can see now how we have much less
   // to pass to res.render(). If we have
   // several routes related to users this
   // can be a great productivity booster
-  res.render('index', { title: 'Users' });
-});
+  res.render('index', { title: 'Users' })
+})
 
 // keep in mind that middleware may be placed anywhere
 // and in various combinations, so if you have locals
@@ -150,6 +144,6 @@ app.all('/api/*', function(req, res, next){
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/examples/view-locals/user.js b/examples/view-locals/user.js
index aaa6f85ff0e..6f29020f4aa 100644
--- a/examples/view-locals/user.js
+++ b/examples/view-locals/user.js
@@ -1,36 +1,36 @@
 'use strict'
 
-module.exports = User;
+module.exports = User
 
 // faux model
 
-function User(name, age, species) {
-  this.name = name;
-  this.age = age;
-  this.species = species;
+function User (name, age, species) {
+  this.name = name
+  this.age = age
+  this.species = species
 }
 
-User.all = function(fn){
+User.all = function (fn) {
   // process.nextTick makes sure this function API
   // behaves in an asynchronous manner, like if it
   // was a real DB query to read all users.
-  process.nextTick(function(){
-    fn(null, users);
-  });
-};
+  process.nextTick(() => {
+    fn(null, users)
+  })
+}
 
-User.count = function(fn){
-  process.nextTick(function(){
-    fn(null, users.length);
-  });
-};
+User.count = function (fn) {
+  process.nextTick(() => {
+    fn(null, users.length)
+  })
+}
 
 // faux database
 
-var users = [];
+const users = []
 
-users.push(new User('Tobi', 2, 'ferret'));
-users.push(new User('Loki', 1, 'ferret'));
-users.push(new User('Jane', 6, 'ferret'));
-users.push(new User('Luna', 1, 'cat'));
-users.push(new User('Manny', 1, 'cat'));
+users.push(new User('Tobi', 2, 'ferret'))
+users.push(new User('Loki', 1, 'ferret'))
+users.push(new User('Jane', 6, 'ferret'))
+users.push(new User('Luna', 1, 'cat'))
+users.push(new User('Manny', 1, 'cat'))
diff --git a/examples/web-service/index.js b/examples/web-service/index.js
index d1a90362153..b7c18601353 100644
--- a/examples/web-service/index.js
+++ b/examples/web-service/index.js
@@ -4,18 +4,18 @@
  * Module dependencies.
  */
 
-var express = require('../../');
+const express = require('../../')
 
-var app = module.exports = express();
+const app = module.exports = express()
 
 // create an error with .status. we
 // can then use the property in our
 // custom error handler (Connect respects this prop as well)
 
-function error(status, msg) {
-  var err = new Error(msg);
-  err.status = status;
-  return err;
+function error (status, msg) {
+  const err = new Error(msg)
+  err.status = status
+  return err
 }
 
 // if we wanted to supply more than JSON, we could
@@ -27,91 +27,91 @@ function error(status, msg) {
 // meaning only paths prefixed with "/api"
 // will cause this middleware to be invoked
 
-app.use('/api', function(req, res, next){
-  var key = req.query['api-key'];
+app.use('/api', (req, res, next) => {
+  const key = req.query['api-key']
 
   // key isn't present
-  if (!key) return next(error(400, 'api key required'));
+  if (!key) return next(error(400, 'api key required'))
 
   // key is invalid
   if (apiKeys.indexOf(key) === -1) return next(error(401, 'invalid api key'))
 
   // all good, store req.key for route access
-  req.key = key;
-  next();
-});
+  req.key = key
+  next()
+})
 
 // map of valid api keys, typically mapped to
 // account info with some sort of database like redis.
 // api keys do _not_ serve as authentication, merely to
 // track API usage or help prevent malicious behavior etc.
 
-var apiKeys = ['foo', 'bar', 'baz'];
+const apiKeys = ['foo', 'bar', 'baz']
 
 // these two objects will serve as our faux database
 
-var repos = [
+const repos = [
   { name: 'express', url: 'https://github.com/expressjs/express' },
   { name: 'stylus', url: 'https://github.com/learnboost/stylus' },
   { name: 'cluster', url: 'https://github.com/learnboost/cluster' }
-];
-
-var users = [
-  { name: 'tobi' }
-  , { name: 'loki' }
-  , { name: 'jane' }
-];
-
-var userRepos = {
-  tobi: [repos[0], repos[1]]
-  , loki: [repos[1]]
-  , jane: [repos[2]]
-};
+]
+
+const users = [
+  { name: 'tobi' },
+  { name: 'loki' },
+  { name: 'jane' }
+]
+
+const userRepos = {
+  tobi: [repos[0], repos[1]],
+  loki: [repos[1]],
+  jane: [repos[2]]
+}
 
 // we now can assume the api key is valid,
 // and simply expose the data
 
 // example: http://localhost:3000/api/users/?api-key=foo
-app.get('/api/users', function (req, res) {
-  res.send(users);
-});
+app.get('/api/users', (req, res) => {
+  res.send(users)
+})
 
 // example: http://localhost:3000/api/repos/?api-key=foo
-app.get('/api/repos', function (req, res) {
-  res.send(repos);
-});
+app.get('/api/repos', (req, res) => {
+  res.send(repos)
+})
 
 // example: http://localhost:3000/api/user/tobi/repos/?api-key=foo
-app.get('/api/user/:name/repos', function(req, res, next){
-  var name = req.params.name;
-  var user = userRepos[name];
+app.get('/api/user/:name/repos', (req, res, next) => {
+  const name = req.params.name
+  const user = userRepos[name]
 
-  if (user) res.send(user);
-  else next();
-});
+  if (user) res.send(user)
+  else next()
+})
 
 // middleware with an arity of 4 are considered
 // error handling middleware. When you next(err)
 // it will be passed through the defined middleware
 // in order, but ONLY those with an arity of 4, ignoring
 // regular middleware.
-app.use(function(err, req, res, next){
+app.use((err, req, res, next) => {
   // whatever you want here, feel free to populate
   // properties on `err` to treat it differently in here.
-  res.status(err.status || 500);
-  res.send({ error: err.message });
-});
+  res.status(err.status || 500)
+  res.send({ error: err.message })
+})
 
 // our custom JSON 404 middleware. Since it's placed last
 // it will be the last middleware called, if all others
 // invoke next() and do not respond.
-app.use(function(req, res){
-  res.status(404);
+app.use((req, res) => {
+  res.status(404)
   res.send({ error: "Sorry, can't find that" })
-});
+})
 
 /* istanbul ignore next */
 if (!module.parent) {
-  app.listen(3000);
-  console.log('Express started on port 3000');
+  app.listen(3000)
+  console.log('Express started on port 3000')
 }
diff --git a/index.js b/index.js
index d219b0c878d..9ae72fdf117 100644
--- a/index.js
+++ b/index.js
@@ -6,6 +6,6 @@
  * MIT Licensed
  */
 
-'use strict';
+'use strict'
 
-module.exports = require('./lib/express');
+module.exports = require('./lib/express')
diff --git a/lib/application.js b/lib/application.js
index 838b882aaae..2a2a5e40c25 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -6,45 +6,42 @@
  * MIT Licensed
  */
 
-'use strict';
+'use strict'
 
 /**
  * Module dependencies.
  * @private
  */
 
-var finalhandler = require('finalhandler');
-var debug = require('debug')('express:application');
-var View = require('./view');
-var http = require('node:http');
-var methods = require('./utils').methods;
-var compileETag = require('./utils').compileETag;
-var compileQueryParser = require('./utils').compileQueryParser;
-var compileTrust = require('./utils').compileTrust;
-var resolve = require('node:path').resolve;
-var once = require('once')
-var Router = require('router');
+const finalhandler = require('finalhandler')
+const debug = require('debug')('express:application')
+const View = require('./view')
+const http = require('node:http')
+const { methods, compileETag, compileQueryParser, compileTrust } = require('./utils')
+const resolve = require('node:path').resolve
+const once = require('once')
+const Router = require('router')
 
 /**
  * Module variables.
  * @private
  */
 
-var slice = Array.prototype.slice;
-var flatten = Array.prototype.flat;
+const slice = Array.prototype.slice
+const flatten = Array.prototype.flat
 
 /**
  * Application prototype.
  */
 
-var app = exports = module.exports = {};
+const app = exports = module.exports = {}
 
 /**
  * Variable for trust proxy inheritance back-compat
  * @private
  */
 
-var trustProxyDefaultSymbol = '@@symbol:trust_proxy_default';
+const trustProxyDefaultSymbol = '@@symbol:trust_proxy_default'
 
 /**
  * Initialize the server.
@@ -56,62 +53,62 @@ var trustProxyDefaultSymbol = '@@symbol:trust_proxy_default';
  * @private
  */
 
-app.init = function init() {
-  var router = null;
+app.init = function init () {
+  let router = null
 
-  this.cache = Object.create(null);
-  this.engines = Object.create(null);
-  this.settings = Object.create(null);
+  this.cache = Object.create(null)
+  this.engines = Object.create(null)
+  this.settings = Object.create(null)
 
-  this.defaultConfiguration();
+  this.defaultConfiguration()
 
   // Setup getting to lazily add base router
   Object.defineProperty(this, 'router', {
     configurable: true,
     enumerable: true,
-    get: function getrouter() {
+    get: function getrouter () {
       if (router === null) {
         router = new Router({
           caseSensitive: this.enabled('case sensitive routing'),
           strict: this.enabled('strict routing')
-        });
+        })
       }
 
-      return router;
+      return router
     }
-  });
-};
+  })
+}
 
 /**
  * Initialize application configuration.
  * @private
  */
 
-app.defaultConfiguration = function defaultConfiguration() {
-  var env = process.env.NODE_ENV || 'development';
+app.defaultConfiguration = function defaultConfiguration () {
+  const env = process.env.NODE_ENV || 'development'
 
   // default settings
-  this.enable('x-powered-by');
-  this.set('etag', 'weak');
-  this.set('env', env);
+  this.enable('x-powered-by')
+  this.set('etag', 'weak')
+  this.set('env', env)
   this.set('query parser', 'simple')
-  this.set('subdomain offset', 2);
-  this.set('trust proxy', false);
+  this.set('subdomain offset', 2)
+  this.set('trust proxy', false)
 
   // trust proxy inherit back-compat
   Object.defineProperty(this.settings, trustProxyDefaultSymbol, {
     configurable: true,
     value: true
-  });
+  })
 
-  debug('booting in %s mode', env);
+  debug('booting in %s mode', env)
 
-  this.on('mount', function onmount(parent) {
+  this.on('mount', function onmount (parent) {
     // inherit trust proxy
-    if (this.settings[trustProxyDefaultSymbol] === true
-      && typeof parent.settings['trust proxy fn'] === 'function') {
-      delete this.settings['trust proxy'];
-      delete this.settings['trust proxy fn'];
+    if (this.settings[trustProxyDefaultSymbol] === true &&
+      typeof parent.settings['trust proxy fn'] === 'function') {
+      delete this.settings['trust proxy']
+      delete this.settings['trust proxy fn']
     }
 
     // inherit protos
@@ -119,26 +116,26 @@ app.defaultConfiguration = function defaultConfiguration() {
     Object.setPrototypeOf(this.response, parent.response)
     Object.setPrototypeOf(this.engines, parent.engines)
     Object.setPrototypeOf(this.settings, parent.settings)
-  });
+  })
 
   // setup locals
-  this.locals = Object.create(null);
+  this.locals = Object.create(null)
 
   // top-most app is mounted at /
-  this.mountpath = '/';
+  this.mountpath = '/'
 
   // default locals
-  this.locals.settings = this.settings;
+  this.locals.settings = this.settings
 
   // default configuration
-  this.set('view', View);
-  this.set('views', resolve('views'));
-  this.set('jsonp callback name', 'callback');
+  this.set('view', View)
+  this.set('views', resolve('views'))
+  this.set('jsonp callback name', 'callback')
 
   if (env === 'production') {
-    this.enable('view cache');
+    this.enable('view cache')
   }
-};
+}
 
 /**
  * Dispatch a req, res pair into the application. Starts pipeline processing.
@@ -149,21 +146,21 @@ app.defaultConfiguration = function defaultConfiguration() {
  * @private
  */
 
-app.handle = function handle(req, res, callback) {
+app.handle = function handle (req, res, callback) {
   // final handler
-  var done = callback || finalhandler(req, res, {
+  const done = callback || finalhandler(req, res, {
     env: this.get('env'),
     onerror: logerror.bind(this)
-  });
+  })
 
   // set powered by header
   if (this.enabled('x-powered-by')) {
-    res.setHeader('X-Powered-By', 'Express');
+    res.setHeader('X-Powered-By', 'Express')
   }
 
   // set circular references
-  req.res = res;
-  res.req = req;
+  req.res = res
+  res.req = req
 
   // alter the prototypes
   Object.setPrototypeOf(req, this.request)
@@ -171,11 +168,11 @@ app.handle = function handle(req, res, callback) {
 
   // setup locals
   if (!res.locals) {
-    res.locals = Object.create(null);
+    res.locals = Object.create(null)
   }
 
-  this.router.handle(req, res, done);
-};
+  this.router.handle(req, res, done)
+}
 
 /**
  * Proxy `Router#use()` to add middleware to the app router.
@@ -187,61 +184,61 @@ app.handle = function handle(req, res, callback) {
  * @public
  */
 
-app.use = function use(fn) {
-  var offset = 0;
-  var path = '/';
+app.use = function use (fn) {
+  let offset = 0
+  let path = '/'
 
   // default path to '/'
   // disambiguate app.use([fn])
   if (typeof fn !== 'function') {
-    var arg = fn;
+    let arg = fn
 
     while (Array.isArray(arg) && arg.length !== 0) {
-      arg = arg[0];
+      arg = arg[0]
     }
 
     // first arg is the path
     if (typeof arg !== 'function') {
-      offset = 1;
-      path = fn;
+      offset = 1
+      path = fn
     }
   }
 
-  var fns = flatten.call(slice.call(arguments, offset), Infinity);
+  const fns = flatten.call(slice.call(arguments, offset), Infinity)
 
   if (fns.length === 0) {
     throw new TypeError('app.use() requires a middleware function')
   }
 
   // get router
-  var router = this.router;
+  const router = this.router
 
   fns.forEach(function (fn) {
     // non-express app
     if (!fn || !fn.handle || !fn.set) {
-      return router.use(path, fn);
+      return router.use(path, fn)
     }
 
-    debug('.use app under %s', path);
-    fn.mountpath = path;
-    fn.parent = this;
+    debug('.use app under %s', path)
+    fn.mountpath = path
+    fn.parent = this
 
     // restore .app property on req and res
-    router.use(path, function mounted_app(req, res, next) {
-      var orig = req.app;
-      fn.handle(req, res, function (err) {
+    router.use(path, function mountedApp (req, res, next) {
+      const orig = req.app
+      fn.handle(req, res, (err) => {
         Object.setPrototypeOf(req, orig.request)
         Object.setPrototypeOf(res, orig.response)
-        next(err);
-      });
-    });
+        next(err)
+      })
+    })
 
     // mounted an app
-    fn.emit('mount', this);
-  }, this);
+    fn.emit('mount', this)
+  }, this)
 
-  return this;
-};
+  return this
+}
 
 /**
  * Proxy to the app `Router#route()`
@@ -253,9 +250,9 @@ app.use = function use(fn) {
  * @public
  */
 
-app.route = function route(path) {
-  return this.router.route(path);
-};
+app.route = function route (path) {
+  return this.router.route(path)
+}
 
 /**
  * Register the given template engine callback `fn`
@@ -291,21 +288,21 @@ app.route = function route(path) {
  * @public
  */
 
-app.engine = function engine(ext, fn) {
+app.engine = function engine (ext, fn) {
   if (typeof fn !== 'function') {
-    throw new Error('callback function required');
+    throw new Error('callback function required')
   }
 
   // get file extension
-  var extension = ext[0] !== '.'
+  const extension = ext[0] !== '.'
     ? '.' + ext
-    : ext;
+    : ext
 
   // store engine
-  this.engines[extension] = fn;
+  this.engines[extension] = fn
 
-  return this;
-};
+  return this
+}
 
 /**
  * Proxy to `Router#param()` with one added api feature. The _name_ parameter
@@ -319,19 +316,19 @@ app.engine = function engine(ext, fn) {
  * @public
  */
 
-app.param = function param(name, fn) {
+app.param = function param (name, fn) {
   if (Array.isArray(name)) {
-    for (var i = 0; i < name.length; i++) {
-      this.param(name[i], fn);
+    for (let i = 0; i < name.length; i++) {
+      this.param(name[i], fn)
     }
 
-    return this;
+    return this
   }
 
-  this.router.param(name, fn);
+  this.router.param(name, fn)
 
-  return this;
-};
+  return this
+}
 
 /**
  * Assign `setting` to `val`, or return `setting`'s value.
@@ -348,39 +345,39 @@ app.param = function param(name, fn) {
  * @public
  */
 
-app.set = function set(setting, val) {
+app.set = function set (setting, val) {
   if (arguments.length === 1) {
     // app.get(setting)
-    return this.settings[setting];
+    return this.settings[setting]
   }
 
-  debug('set "%s" to %o', setting, val);
+  debug('set "%s" to %o', setting, val)
 
   // set value
-  this.settings[setting] = val;
+  this.settings[setting] = val
 
   // trigger matched settings
   switch (setting) {
     case 'etag':
-      this.set('etag fn', compileETag(val));
-      break;
+      this.set('etag fn', compileETag(val))
+      break
     case 'query parser':
-      this.set('query parser fn', compileQueryParser(val));
-      break;
+      this.set('query parser fn', compileQueryParser(val))
+      break
     case 'trust proxy':
-      this.set('trust proxy fn', compileTrust(val));
+      this.set('trust proxy fn', compileTrust(val))
 
       // trust proxy inherit back-compat
       Object.defineProperty(this.settings, trustProxyDefaultSymbol, {
         configurable: true,
         value: false
-      });
+      })
 
-      break;
+      break
   }
 
-  return this;
-};
+  return this
+}
 
 /**
  * Return the app's absolute pathname
@@ -396,11 +393,11 @@ app.set = function set(setting, val) {
  * @private
  */
 
-app.path = function path() {
+app.path = function path () {
   return this.parent
     ? this.parent.path() + this.mountpath
-    : '';
-};
+    : ''
+}
 
 /**
  * Check if `setting` is enabled (truthy).
@@ -417,9 +414,9 @@ app.path = function path() {
  * @public
  */
 
-app.enabled = function enabled(setting) {
-  return Boolean(this.set(setting));
-};
+app.enabled = function enabled (setting) {
+  return Boolean(this.set(setting))
+}
 
 /**
  * Check if `setting` is disabled.
@@ -436,9 +433,9 @@ app.enabled = function enabled(setting) {
  * @public
  */
 
-app.disabled = function disabled(setting) {
-  return !this.set(setting);
-};
+app.disabled = function disabled (setting) {
+  return !this.set(setting)
+}
 
 /**
  * Enable `setting`.
@@ -448,9 +445,9 @@ app.disabled = function disabled(setting) {
  * @public
  */
 
-app.enable = function enable(setting) {
-  return this.set(setting, true);
-};
+app.enable = function enable (setting) {
+  return this.set(setting, true)
+}
 
 /**
  * Disable `setting`.
@@ -460,26 +457,26 @@ app.enable = function enable(setting) {
  * @public
  */
 
-app.disable = function disable(setting) {
-  return this.set(setting, false);
-};
+app.disable = function disable (setting) {
+  return this.set(setting, false)
+}
 
 /**
  * Delegate `.VERB(...)` calls to `router.VERB(...)`.
  */
 
-methods.forEach(function (method) {
+methods.forEach((method) => {
   app[method] = function (path) {
     if (method === 'get' && arguments.length === 1) {
       // app.get(setting)
-      return this.set(path);
+      return this.set(path)
     }
 
-    var route = this.route(path);
-    route[method].apply(route, slice.call(arguments, 1));
-    return this;
-  };
-});
+    const route = this.route(path)
+    route[method].apply(route, slice.call(arguments, 1))
+    return this
+  }
+})
 
 /**
  * Special-cased "all" method, applying the given route `path`,
@@ -491,16 +488,16 @@ methods.forEach(function (method) {
  * @public
  */
 
-app.all = function all(path) {
-  var route = this.route(path);
-  var args = slice.call(arguments, 1);
+app.all = function all (path) {
+  const route = this.route(path)
+  const args = slice.call(arguments, 1)
 
-  for (var i = 0; i < methods.length; i++) {
-    route[methods[i]].apply(route, args);
+  for (let i = 0; i < methods.length; i++) {
+    route[methods[i]].apply(route, args)
   }
 
-  return this;
-};
+  return this
+}
 
 /**
  * Render the given view `name` name with `options`
@@ -519,60 +516,60 @@ app.all = function all(path) {
  * @public
  */
 
-app.render = function render(name, options, callback) {
-  var cache = this.cache;
-  var done = callback;
-  var engines = this.engines;
-  var opts = options;
-  var view;
+app.render = function render (name, options, callback) {
+  const cache = this.cache
+  let done = callback
+  const engines = this.engines
+  let opts = options
+  let view
 
   // support callback function as second arg
   if (typeof options === 'function') {
-    done = options;
-    opts = {};
+    done = options
+    opts = {}
   }
 
   // merge options
-  var renderOptions = { ...this.locals, ...opts._locals, ...opts };
+  const renderOptions = { ...this.locals, ...opts._locals, ...opts }
 
   // set .cache unless explicitly provided
   if (renderOptions.cache == null) {
-    renderOptions.cache = this.enabled('view cache');
+    renderOptions.cache = this.enabled('view cache')
   }
 
   // primed cache
   if (renderOptions.cache) {
-    view = cache[name];
+    view = cache[name]
   }
 
   // view
   if (!view) {
-    var View = this.get('view');
+    const View = this.get('view')
 
     view = new View(name, {
       defaultEngine: this.get('view engine'),
       root: this.get('views'),
-      engines: engines
-    });
+      engines
+    })
 
     if (!view.path) {
-      var dirs = Array.isArray(view.root) && view.root.length > 1
+      const dirs = Array.isArray(view.root) && view.root.length > 1
         ? 'directories "' + view.root.slice(0, -1).join('", "') + '" or "' + view.root[view.root.length - 1] + '"'
         : 'directory "' + view.root + '"'
-      var err = new Error('Failed to lookup view "' + name + '" in views ' + dirs);
-      err.view = view;
-      return done(err);
+      const err = new Error('Failed to lookup view "' + name + '" in views ' + dirs)
+      err.view = view
+      return done(err)
     }
 
     // prime the cache
     if (renderOptions.cache) {
-      cache[name] = view;
+      cache[name] = view
     }
   }
 
   // render
-  tryRender(view, renderOptions, done);
-};
+  tryRender(view, renderOptions, done)
+}
 
 /**
  * Listen for connections.
@@ -595,11 +592,11 @@ app.render = function render(name, options, callback) {
  * @public
  */
 
-app.listen = function listen() {
-  var server = http.createServer(this)
-  var args = slice.call(arguments)
+app.listen = function listen () {
+  const server = http.createServer(this)
+  const args = slice.call(arguments)
   if (typeof args[args.length - 1] === 'function') {
-    var done = args[args.length - 1] = once(args[args.length - 1])
+    const done = args[args.length - 1] = once(args[args.length - 1])
     server.once('error', done)
   }
   return server.listen.apply(server, args)
@@ -612,9 +609,9 @@ app.listen = function listen() {
  * @private
  */
 
-function logerror(err) {
+function logerror (err) {
   /* istanbul ignore next */
-  if (this.get('env') !== 'test') console.error(err.stack || err.toString());
+  if (this.get('env') !== 'test') console.error(err.stack || err.toString())
 }
 
 /**
@@ -622,10 +619,10 @@ function logerror(err) {
  * @private
  */
 
-function tryRender(view, options, callback) {
+function tryRender (view, options, callback) {
   try {
-    view.render(options, callback);
+    view.render(options, callback)
   } catch (err) {
-    callback(err);
+    callback(err)
   }
 }
diff --git a/lib/express.js b/lib/express.js
index 2d502eb54e4..43a1b0b280c 100644
--- a/lib/express.js
+++ b/lib/express.js
@@ -6,25 +6,25 @@
  * MIT Licensed
  */
 
-'use strict';
+'use strict'
 
 /**
  * Module dependencies.
  */
 
-var bodyParser = require('body-parser')
-var EventEmitter = require('node:events').EventEmitter;
-var mixin = require('merge-descriptors');
-var proto = require('./application');
-var Router = require('router');
-var req = require('./request');
-var res = require('./response');
+const bodyParser = require('body-parser')
+const { EventEmitter } = require('node:events')
+const mixin = require('merge-descriptors')
+const proto = require('./application')
+const Router = require('router')
+const req = require('./request')
+const res = require('./response')
 
 /**
  * Expose `createApplication()`.
  */
 
-exports = module.exports = createApplication;
+exports = module.exports = createApplication
 
 /**
  * Create an express application.
@@ -33,13 +33,13 @@ exports = module.exports = createApplication;
  * @api public
  */
 
-function createApplication() {
-  var app = function(req, res, next) {
-    app.handle(req, res, next);
-  };
+function createApplication () {
+  const app = function (req, res, next) {
+    app.handle(req, res, next)
+  }
 
-  mixin(app, EventEmitter.prototype, false);
-  mixin(app, proto, false);
+  mixin(app, EventEmitter.prototype, false)
+  mixin(app, proto, false)
 
   // expose the prototype that will get set on requests
   app.request = Object.create(req, {
@@ -51,24 +51,24 @@ function createApplication() {
     app: { configurable: true, enumerable: true, writable: true, value: app }
   })
 
-  app.init();
-  return app;
+  app.init()
+  return app
 }
 
 /**
  * Expose the prototypes.
  */
 
-exports.application = proto;
-exports.request = req;
-exports.response = res;
+exports.application = proto
+exports.request = req
+exports.response = res
 
 /**
  * Expose constructors.
  */
 
-exports.Route = Router.Route;
-exports.Router = Router;
+exports.Route = Router.Route
+exports.Router = Router
 
 /**
  * Expose middleware
@@ -76,6 +76,6 @@ exports.Router = Router;
 
 exports.json = bodyParser.json
 exports.raw = bodyParser.raw
-exports.static = require('serve-static');
+exports.static = require('serve-static')
 exports.text = bodyParser.text
 exports.urlencoded = bodyParser.urlencoded
diff --git a/lib/request.js b/lib/request.js
index 69990da39b6..369bf34e966 100644
--- a/lib/request.js
+++ b/lib/request.js
@@ -6,28 +6,28 @@
  * MIT Licensed
  */
 
-'use strict';
+'use strict'
 
 /**
  * Module dependencies.
  * @private
  */
 
-var accepts = require('accepts');
-var isIP = require('node:net').isIP;
-var typeis = require('type-is');
-var http = require('node:http');
-var fresh = require('fresh');
-var parseRange = require('range-parser');
-var parse = require('parseurl');
-var proxyaddr = require('proxy-addr');
+const accepts = require('accepts')
+const { isIP } = require('node:net')
+const typeis = require('type-is')
+const http = require('node:http')
+const fresh = require('fresh')
+const parseRange = require('range-parser')
+const parse = require('parseurl')
+const proxyaddr = require('proxy-addr')
 
 /**
  * Request prototype.
  * @public
  */
 
-var req = Object.create(http.IncomingMessage.prototype)
+const req = Object.create(http.IncomingMessage.prototype)
 
 /**
  * Module exports.
@@ -61,26 +61,26 @@ module.exports = req
  */
 
 req.get =
-req.header = function header(name) {
+req.header = function header (name) {
   if (!name) {
-    throw new TypeError('name argument is required to req.get');
+    throw new TypeError('name argument is required to req.get')
   }
 
   if (typeof name !== 'string') {
-    throw new TypeError('name must be a string to req.get');
+    throw new TypeError('name must be a string to req.get')
   }
 
-  var lc = name.toLowerCase();
+  const lc = name.toLowerCase()
 
   switch (lc) {
     case 'referer':
     case 'referrer':
-      return this.headers.referrer
-        || this.headers.referer;
+      return this.headers.referrer ||
+        this.headers.referer
     default:
-      return this.headers[lc];
+      return this.headers[lc]
   }
-};
+}
 
 /**
  * To do: update docs.
@@ -128,10 +128,10 @@ req.header = function header(name) {
  * @public
  */
 
-req.accepts = function(){
-  var accept = accepts(this);
-  return accept.types.apply(accept, arguments);
-};
+req.accepts = function () {
+  const accept = accepts(this)
+  return accept.types.apply(accept, arguments)
+}
 
 /**
  * Check if the given `encoding`s are accepted.
@@ -141,10 +141,10 @@ req.accepts = function(){
  * @public
  */
 
-req.acceptsEncodings = function(){
-  var accept = accepts(this);
-  return accept.encodings.apply(accept, arguments);
-};
+req.acceptsEncodings = function () {
+  const accept = accepts(this)
+  return accept.encodings.apply(accept, arguments)
+}
 
 /**
  * Check if the given `charset`s are acceptable,
@@ -155,10 +155,10 @@ req.acceptsEncodings = function(){
  * @public
  */
 
-req.acceptsCharsets = function(){
-  var accept = accepts(this);
-  return accept.charsets.apply(accept, arguments);
-};
+req.acceptsCharsets = function () {
+  const accept = accepts(this)
+  return accept.charsets.apply(accept, arguments)
+}
 
 /**
  * Check if the given `lang`s are acceptable,
@@ -169,9 +169,9 @@ req.acceptsCharsets = function(){
  * @public
  */
 
-req.acceptsLanguages = function(...languages) {
-  return accepts(this).languages(...languages);
-};
+req.acceptsLanguages = function (...languages) {
+  return accepts(this).languages(...languages)
+}
 
 /**
  * Parse Range header field, capping to the given `size`.
@@ -198,11 +198,11 @@ req.acceptsLanguages = function(...languages) {
  * @public
  */
 
-req.range = function range(size, options) {
-  var range = this.get('Range');
-  if (!range) return;
-  return parseRange(size, range, options);
-};
+req.range = function range (size, options) {
+  const range = this.get('Range')
+  if (!range) return
+  return parseRange(size, range, options)
+}
 
 /**
  * Parse the query string of `req.url`.
@@ -214,18 +214,18 @@ req.range = function range(size, options) {
  * @api public
  */
 
-defineGetter(req, 'query', function query(){
-  var queryparse = this.app.get('query parser fn');
+defineGetter(req, 'query', function query () {
+  const queryparse = this.app.get('query parser fn')
 
   if (!queryparse) {
     // parsing is disabled
-    return Object.create(null);
+    return Object.create(null)
   }
 
-  var querystring = parse(this).query;
+  const querystring = parse(this).query
 
-  return queryparse(querystring);
-});
+  return queryparse(querystring)
+})
 
 /**
  * Check if the incoming request contains the "Content-Type"
@@ -253,19 +253,19 @@ defineGetter(req, 'query', function query(){
  * @public
  */
 
-req.is = function is(types) {
-  var arr = types;
+req.is = function is (types) {
+  let arr = types
 
   // support flattened arguments
   if (!Array.isArray(types)) {
-    arr = new Array(arguments.length);
-    for (var i = 0; i < arr.length; i++) {
-      arr[i] = arguments[i];
+    arr = new Array(arguments.length)
+    for (let i = 0; i < arr.length; i++) {
+      arr[i] = arguments[i]
     }
   }
 
-  return typeis(this, arr);
-};
+  return typeis(this, arr)
+}
 
 /**
  * Return the protocol string "http" or "https"
@@ -281,25 +281,25 @@ req.is = function is(types) {
  * @public
  */
 
-defineGetter(req, 'protocol', function protocol(){
-  var proto = this.socket.encrypted
+defineGetter(req, 'protocol', function protocol () {
+  const proto = this.socket.encrypted
     ? 'https'
-    : 'http';
-  var trust = this.app.get('trust proxy fn');
+    : 'http'
+  const trust = this.app.get('trust proxy fn')
 
   if (!trust(this.socket.remoteAddress, 0)) {
-    return proto;
+    return proto
   }
 
   // Note: X-Forwarded-Proto is normally only ever a
   //       single value, but this is to be safe.
-  var header = this.get('X-Forwarded-Proto') || proto
-  var index = header.indexOf(',')
+  const header = this.get('X-Forwarded-Proto') || proto
+  const index = header.indexOf(',')
 
   return index !== -1
     ? header.substring(0, index).trim()
     : header.trim()
-});
+})
 
 /**
  * Short-hand for:
@@ -310,9 +310,9 @@ defineGetter(req, 'protocol', function protocol(){
  * @public
  */
 
-defineGetter(req, 'secure', function secure(){
-  return this.protocol === 'https';
-});
+defineGetter(req, 'secure', function secure () {
+  return this.protocol === 'https'
+})
 
 /**
  * Return the remote address from the trusted proxy.
@@ -324,10 +324,10 @@ defineGetter(req, 'secure', function secure(){
  * @public
  */
 
-defineGetter(req, 'ip', function ip(){
-  var trust = this.app.get('trust proxy fn');
-  return proxyaddr(this, trust);
-});
+defineGetter(req, 'ip', function ip () {
+  const trust = this.app.get('trust proxy fn')
+  return proxyaddr(this, trust)
+})
 
 /**
  * When "trust proxy" is set, trusted proxy addresses + client.
@@ -341,16 +341,16 @@ defineGetter(req, 'ip', function ip(){
  * @public
  */
 
-defineGetter(req, 'ips', function ips() {
-  var trust = this.app.get('trust proxy fn');
-  var addrs = proxyaddr.all(this, trust);
+defineGetter(req, 'ips', function ips () {
+  const trust = this.app.get('trust proxy fn')
+  const addrs = proxyaddr.all(this, trust)
 
   // reverse the order (to farthest -> closest)
   // and remove socket address
   addrs.reverse().pop()
 
   return addrs
-});
+})
 
 /**
  * Return subdomains as an array.
@@ -367,18 +367,18 @@ defineGetter(req, 'ips', function ips() {
  * @public
  */
 
-defineGetter(req, 'subdomains', function subdomains() {
-  var hostname = this.hostname;
+defineGetter(req, 'subdomains', function subdomains () {
+  const hostname = this.hostname
 
-  if (!hostname) return [];
+  if (!hostname) return []
 
-  var offset = this.app.get('subdomain offset');
-  var subdomains = !isIP(hostname)
+  const offset = this.app.get('subdomain offset')
+  const subdomains = !isIP(hostname)
     ? hostname.split('.').reverse()
-    : [hostname];
+    : [hostname]
 
-  return subdomains.slice(offset);
-});
+  return subdomains.slice(offset)
+})
 
 /**
  * Short-hand for `url.parse(req.url).pathname`.
@@ -387,9 +387,9 @@ defineGetter(req, 'subdomains', function subdomains() {
  * @public
  */
 
-defineGetter(req, 'path', function path() {
-  return parse(this).pathname;
-});
+defineGetter(req, 'path', function path () {
+  return parse(this).pathname
+})
 
 /**
  * Parse the "Host" header field to a host.
@@ -402,20 +402,20 @@ defineGetter(req, 'path', function path() {
  * @public
  */
 
-defineGetter(req, 'host', function host(){
-  var trust = this.app.get('trust proxy fn');
-  var val = this.get('X-Forwarded-Host');
+defineGetter(req, 'host', function host () {
+  const trust = this.app.get('trust proxy fn')
+  let val = this.get('X-Forwarded-Host')
 
   if (!val || !trust(this.socket.remoteAddress, 0)) {
-    val = this.get('Host');
+    val = this.get('Host')
   } else if (val.indexOf(',') !== -1) {
     // Note: X-Forwarded-Host is normally only ever a
     //       single value, but this is to be safe.
     val = val.substring(0, val.indexOf(',')).trimRight()
   }
 
-  return val || undefined;
-});
+  return val || undefined
+})
 
 /**
  * Parse the "Host" header field to a hostname.
@@ -428,21 +428,21 @@ defineGetter(req, 'host', function host(){
  * @api public
  */
 
-defineGetter(req, 'hostname', function hostname(){
-  var host = this.host;
+defineGetter(req, 'hostname', function hostname () {
+  const host = this.host
 
-  if (!host) return;
+  if (!host) return
 
   // IPv6 literal support
-  var offset = host[0] === '['
+  const offset = host[0] === '['
     ? host.indexOf(']') + 1
-    : 0;
-  var index = host.indexOf(':', offset);
+    : 0
+  const index = host.indexOf(':', offset)
 
   return index !== -1
     ? host.substring(0, index)
-    : host;
-});
+    : host
+})
 
 /**
  * Check if the request is fresh, aka
@@ -453,24 +453,24 @@ defineGetter(req, 'hostname', function hostname(){
  * @public
  */
 
-defineGetter(req, 'fresh', function(){
-  var method = this.method;
-  var res = this.res
-  var status = res.statusCode
+defineGetter(req, 'fresh', function () {
+  const method = this.method
+  const res = this.res
+  const status = res.statusCode
 
   // GET or HEAD for weak freshness validation only
-  if ('GET' !== method && 'HEAD' !== method) return false;
+  if (method !== 'GET' && method !== 'HEAD') return false
 
   // 2xx or 304 as per rfc2616 14.26
-  if ((status >= 200 && status < 300) || 304 === status) {
+  if ((status >= 200 && status < 300) || status === 304) {
     return fresh(this.headers, {
-      'etag': res.get('ETag'),
+      etag: res.get('ETag'),
       'last-modified': res.get('Last-Modified')
     })
   }
 
-  return false;
-});
+  return false
+})
 
 /**
  * Check if the request is stale, aka
@@ -481,9 +481,9 @@ defineGetter(req, 'fresh', function(){
  * @public
  */
 
-defineGetter(req, 'stale', function stale(){
-  return !this.fresh;
-});
+defineGetter(req, 'stale', function stale () {
+  return !this.fresh
+})
 
 /**
  * Check if the request was an _XMLHttpRequest_.
@@ -492,10 +492,10 @@ defineGetter(req, 'stale', function stale(){
  * @public
  */
 
-defineGetter(req, 'xhr', function xhr(){
-  var val = this.get('X-Requested-With') || '';
-  return val.toLowerCase() === 'xmlhttprequest';
-});
+defineGetter(req, 'xhr', function xhr () {
+  const val = this.get('X-Requested-With') || ''
+  return val.toLowerCase() === 'xmlhttprequest'
+})
 
 /**
  * Helper function for creating a getter on an object.
@@ -505,10 +505,10 @@ defineGetter(req, 'xhr', function xhr(){
  * @param {Function} getter
  * @private
  */
-function defineGetter(obj, name, getter) {
+function defineGetter (obj, name, getter) {
   Object.defineProperty(obj, name, {
     configurable: true,
     enumerable: true,
     get: getter
-  });
+  })
 }
diff --git a/lib/response.js b/lib/response.js
index 7a2f0ecce56..74d9c58c935 100644
--- a/lib/response.js
+++ b/lib/response.js
@@ -5,41 +5,39 @@
  * MIT Licensed
  */
 
-'use strict';
+'use strict'
 
 /**
  * Module dependencies.
  * @private
  */
 
-var contentDisposition = require('content-disposition');
-var createError = require('http-errors')
-var deprecate = require('depd')('express');
-var encodeUrl = require('encodeurl');
-var escapeHtml = require('escape-html');
-var http = require('node:http');
-var onFinished = require('on-finished');
-var mime = require('mime-types')
-var path = require('node:path');
-var pathIsAbsolute = require('node:path').isAbsolute;
-var statuses = require('statuses')
-var sign = require('cookie-signature').sign;
-var normalizeType = require('./utils').normalizeType;
-var normalizeTypes = require('./utils').normalizeTypes;
-var setCharset = require('./utils').setCharset;
-var cookie = require('cookie');
-var send = require('send');
-var extname = path.extname;
-var resolve = path.resolve;
-var vary = require('vary');
-const { Buffer } = require('node:buffer');
+const contentDisposition = require('content-disposition')
+const createError = require('http-errors')
+const deprecate = require('depd')('express')
+const encodeUrl = require('encodeurl')
+const escapeHtml = require('escape-html')
+const http = require('node:http')
+const onFinished = require('on-finished')
+const mime = require('mime-types')
+const path = require('node:path')
+const pathIsAbsolute = path.isAbsolute
+const statuses = require('statuses')
+const { sign } = require('cookie-signature')
+const { normalizeType, normalizeTypes, setCharset } = require('./utils')
+const cookie = require('cookie')
+const send = require('send')
+const extname = path.extname
+const resolve = path.resolve
+const vary = require('vary')
+const { Buffer } = require('node:buffer')
 
 /**
  * Response prototype.
  * @public
  */
 
-var res = Object.create(http.ServerResponse.prototype)
+const res = Object.create(http.ServerResponse.prototype)
 
 /**
  * Module exports.
@@ -61,19 +59,19 @@ module.exports = res
  * @public
  */
 
-res.status = function status(code) {
+res.status = function status (code) {
   // Check if the status code is not an integer
   if (!Number.isInteger(code)) {
-    throw new TypeError(`Invalid status code: ${JSON.stringify(code)}. Status code must be an integer.`);
+    throw new TypeError(`Invalid status code: ${JSON.stringify(code)}. Status code must be an integer.`)
   }
   // Check if the status code is outside of Node's valid range
   if (code < 100 || code > 999) {
-    throw new RangeError(`Invalid status code: ${JSON.stringify(code)}. Status code must be greater than 99 and less than 1000.`);
+    throw new RangeError(`Invalid status code: ${JSON.stringify(code)}. Status code must be greater than 99 and less than 1000.`)
   }
 
-  this.statusCode = code;
-  return this;
-};
+  this.statusCode = code
+  return this
+}
 
 /**
  * Set Link header field with the given `links`.
@@ -94,20 +92,20 @@ res.status = function status(code) {
  * @public
  */
 
-res.links = function(links) {
-  var link = this.get('Link') || '';
-  if (link) link += ', ';
-  return this.set('Link', link + Object.keys(links).map(function(rel) {
+res.links = function (links) {
+  let link = this.get('Link') || ''
+  if (link) link += ', '
+  return this.set('Link', link + Object.keys(links).map((rel) => {
     // Allow multiple links if links[rel] is an array
     if (Array.isArray(links[rel])) {
-      return links[rel].map(function (singleLink) {
-        return `<${singleLink}>; rel="${rel}"`;
-      }).join(', ');
+      return links[rel].map((singleLink) => {
+        return `<${singleLink}>; rel="${rel}"`
+      }).join(', ')
     } else {
-      return `<${links[rel]}>; rel="${rel}"`;
+      return `<${links[rel]}>; rel="${rel}"`
     }
-  }).join(', '));
-};
+  }).join(', '))
+}
 
 /**
  * Send a response.
@@ -122,54 +120,54 @@ res.links = function(links) {
  * @public
  */
 
-res.send = function send(body) {
-  var chunk = body;
-  var encoding;
-  var req = this.req;
-  var type;
+res.send = function send (body) {
+  let chunk = body
+  let encoding
+  const req = this.req
+  let type
 
   // settings
-  var app = this.app;
+  const app = this.app
 
   switch (typeof chunk) {
     // string defaulting to html
     case 'string':
       if (!this.get('Content-Type')) {
-        this.type('html');
+        this.type('html')
       }
-      break;
+      break
     case 'boolean':
     case 'number':
     case 'object':
       if (chunk === null) {
-        chunk = '';
+        chunk = ''
       } else if (ArrayBuffer.isView(chunk)) {
         if (!this.get('Content-Type')) {
-          this.type('bin');
+          this.type('bin')
         }
       } else {
-        return this.json(chunk);
+        return this.json(chunk)
       }
-      break;
+      break
   }
 
   // write strings in utf-8
   if (typeof chunk === 'string') {
-    encoding = 'utf8';
-    type = this.get('Content-Type');
+    encoding = 'utf8'
+    type = this.get('Content-Type')
 
     // reflect this in content-type
     if (typeof type === 'string') {
-      this.set('Content-Type', setCharset(type, 'utf-8'));
+      this.set('Content-Type', setCharset(type, 'utf-8'))
     }
   }
 
   // determine if ETag should be generated
-  var etagFn = app.get('etag fn')
-  var generateETag = !this.get('ETag') && typeof etagFn === 'function'
+  const etagFn = app.get('etag fn')
+  const generateETag = !this.get('ETag') && typeof etagFn === 'function'
 
   // populate Content-Length
-  var len
+  let len
   if (chunk !== undefined) {
     if (Buffer.isBuffer(chunk)) {
       // get length of Buffer
@@ -180,30 +178,30 @@ res.send = function send(body) {
     } else {
       // convert chunk to Buffer and calculate
       chunk = Buffer.from(chunk, encoding)
-      encoding = undefined;
+      encoding = undefined
       len = chunk.length
     }
 
-    this.set('Content-Length', len);
+    this.set('Content-Length', len)
   }
 
   // populate ETag
-  var etag;
+  let etag
   if (generateETag && len !== undefined) {
     if ((etag = etagFn(chunk, encoding))) {
-      this.set('ETag', etag);
+      this.set('ETag', etag)
     }
   }
 
   // freshness
-  if (req.fresh) this.status(304);
+  if (req.fresh) this.status(304)
 
   // strip irrelevant headers
-  if (204 === this.statusCode || 304 === this.statusCode) {
-    this.removeHeader('Content-Type');
-    this.removeHeader('Content-Length');
-    this.removeHeader('Transfer-Encoding');
-    chunk = '';
+  if (this.statusCode === 204 || this.statusCode === 304) {
+    this.removeHeader('Content-Type')
+    this.removeHeader('Content-Length')
+    this.removeHeader('Transfer-Encoding')
+    chunk = ''
   }
 
   // alter headers for 205
@@ -215,14 +213,14 @@ res.send = function send(body) {
 
   if (req.method === 'HEAD') {
     // skip body for HEAD
-    this.end();
+    this.end()
   } else {
     // respond
-    this.end(chunk, encoding);
+    this.end(chunk, encoding)
   }
 
-  return this;
-};
+  return this
+}
 
 /**
  * Send JSON response.
@@ -236,21 +234,21 @@ res.send = function send(body) {
  * @public
  */
 
-res.json = function json(obj) {
+res.json = function json (obj) {
   // settings
-  var app = this.app;
-  var escape = app.get('json escape')
-  var replacer = app.get('json replacer');
-  var spaces = app.get('json spaces');
-  var body = stringify(obj, replacer, spaces, escape)
+  const app = this.app
+  const escape = app.get('json escape')
+  const replacer = app.get('json replacer')
+  const spaces = app.get('json spaces')
+  const body = stringify(obj, replacer, spaces, escape)
 
   // content-type
   if (!this.get('Content-Type')) {
-    this.set('Content-Type', 'application/json');
+    this.set('Content-Type', 'application/json')
   }
 
-  return this.send(body);
-};
+  return this.send(body)
+}
 
 /**
  * Send JSON response with JSONP callback support.
@@ -264,33 +262,33 @@ res.json = function json(obj) {
  * @public
  */
 
-res.jsonp = function jsonp(obj) {
+res.jsonp = function jsonp (obj) {
   // settings
-  var app = this.app;
-  var escape = app.get('json escape')
-  var replacer = app.get('json replacer');
-  var spaces = app.get('json spaces');
-  var body = stringify(obj, replacer, spaces, escape)
-  var callback = this.req.query[app.get('jsonp callback name')];
+  const app = this.app
+  const escape = app.get('json escape')
+  const replacer = app.get('json replacer')
+  const spaces = app.get('json spaces')
+  let body = stringify(obj, replacer, spaces, escape)
+  let callback = this.req.query[app.get('jsonp callback name')]
 
   // content-type
   if (!this.get('Content-Type')) {
-    this.set('X-Content-Type-Options', 'nosniff');
-    this.set('Content-Type', 'application/json');
+    this.set('X-Content-Type-Options', 'nosniff')
+    this.set('Content-Type', 'application/json')
   }
 
   // fixup callback
   if (Array.isArray(callback)) {
-    callback = callback[0];
+    callback = callback[0]
   }
 
   // jsonp
   if (typeof callback === 'string' && callback.length !== 0) {
-    this.set('X-Content-Type-Options', 'nosniff');
-    this.set('Content-Type', 'text/javascript');
+    this.set('X-Content-Type-Options', 'nosniff')
+    this.set('Content-Type', 'text/javascript')
 
     // restrict callback charset
-    callback = callback.replace(/[^\[\]\w$.]/g, '');
+    callback = callback.replace(/[^[\]\w$.]/g, '')
 
     if (body === undefined) {
       // empty argument
@@ -304,11 +302,11 @@ res.jsonp = function jsonp(obj) {
 
     // the /**/ is a specific security mitigation for "Rosetta Flash JSONP abuse"
     // the typeof check is just to reduce client error noise
-    body = '/**/ typeof ' + callback + ' === \'function\' && ' + callback + '(' + body + ');';
+    body = '/**/ typeof ' + callback + ' === \'function\' && ' + callback + '(' + body + ');'
   }
 
-  return this.send(body);
-};
+  return this.send(body)
+}
 
 /**
  * Send given HTTP status code.
@@ -325,14 +323,14 @@ res.jsonp = function jsonp(obj) {
  * @public
  */
 
-res.sendStatus = function sendStatus(statusCode) {
-  var body = statuses.message[statusCode] || String(statusCode)
+res.sendStatus = function sendStatus (statusCode) {
+  const body = statuses.message[statusCode] || String(statusCode)
 
-  this.status(statusCode);
-  this.type('txt');
+  this.status(statusCode)
+  this.type('txt')
 
-  return this.send(body);
-};
+  return this.send(body)
+}
 
 /**
  * Transfer the file at the given `path`.
@@ -375,15 +373,15 @@ res.sendStatus = function sendStatus(statusCode) {
  * @public
  */
 
-res.sendFile = function sendFile(path, options, callback) {
-  var done = callback;
-  var req = this.req;
-  var res = this;
-  var next = req.next;
-  var opts = options || {};
+res.sendFile = function sendFile (path, options, callback) {
+  let done = callback
+  const req = this.req
+  const res = this
+  const next = req.next
+  let opts = options || {}
 
   if (!path) {
-    throw new TypeError('path argument is required to res.sendFile');
+    throw new TypeError('path argument is required to res.sendFile')
   }
 
   if (typeof path !== 'string') {
@@ -392,32 +390,32 @@ res.sendFile = function sendFile(path, options, callback) {
 
   // support function as second arg
   if (typeof options === 'function') {
-    done = options;
-    opts = {};
+    done = options
+    opts = {}
   }
 
   if (!opts.root && !pathIsAbsolute(path)) {
-    throw new TypeError('path must be absolute or specify root to res.sendFile');
+    throw new TypeError('path must be absolute or specify root to res.sendFile')
   }
 
   // create file stream
-  var pathname = encodeURI(path);
+  const pathname = encodeURI(path)
 
   // wire application etag option to send
-  opts.etag = this.app.enabled('etag');
-  var file = send(req, pathname, opts);
+  opts.etag = this.app.enabled('etag')
+  const file = send(req, pathname, opts)
 
   // transfer
-  sendfile(res, file, opts, function (err) {
-    if (done) return done(err);
-    if (err && err.code === 'EISDIR') return next();
+  sendfile(res, file, opts, (err) => {
+    if (done) return done(err)
+    if (err && err.code === 'EISDIR') return next()
 
     // next() all but write errors
     if (err && err.code !== 'ECONNABORTED' && err.syscall !== 'write') {
-      next(err);
+      next(err)
     }
-  });
-};
+  })
+}
 
 /**
  * Transfer the file at the given `path` as an attachment.
@@ -438,14 +436,14 @@ res.sendFile = function sendFile(path, options, callback) {
  */
 
 res.download = function download (path, filename, options, callback) {
-  var done = callback;
-  var name = filename;
-  var opts = options || null
+  let done = callback
+  let name = filename
+  let opts = options || null
 
   // support function as second or third arg
   if (typeof filename === 'function') {
-    done = filename;
-    name = null;
+    done = filename
+    name = null
     opts = null
   } else if (typeof options === 'function') {
     done = options
@@ -460,15 +458,15 @@ res.download = function download (path, filename, options, callback) {
   }
 
   // set Content-Disposition when file is sent
-  var headers = {
+  const headers = {
     'Content-Disposition': contentDisposition(name || path)
-  };
+  }
 
   // merge user-provided headers
   if (opts && opts.headers) {
-    var keys = Object.keys(opts.headers)
-    for (var i = 0; i < keys.length; i++) {
-      var key = keys[i]
+    const keys = Object.keys(opts.headers)
+    for (let i = 0; i < keys.length; i++) {
+      const key = keys[i]
       if (key.toLowerCase() !== 'content-disposition') {
         headers[key] = opts.headers[key]
       }
@@ -480,13 +478,13 @@ res.download = function download (path, filename, options, callback) {
   opts.headers = headers
 
   // Resolve the full path for sendFile
-  var fullPath = !opts.root
+  const fullPath = !opts.root
     ? resolve(path)
     : path
 
   // send file
   return this.sendFile(fullPath, opts, done)
-};
+}
 
 /**
  * Set _Content-Type_ response header with `type` through `mime.contentType()`
@@ -508,13 +506,13 @@ res.download = function download (path, filename, options, callback) {
  */
 
 res.contentType =
-res.type = function contentType(type) {
-  var ct = type.indexOf('/') === -1
+res.type = function contentType (type) {
+  const ct = type.indexOf('/') === -1
     ? (mime.contentType(type) || 'application/octet-stream')
-    : type;
+    : type
 
-  return this.set('Content-Type', ct);
-};
+  return this.set('Content-Type', ct)
+}
 
 /**
  * Respond to the Acceptable formats using an `obj`
@@ -573,32 +571,32 @@ res.type = function contentType(type) {
  * @public
  */
 
-res.format = function(obj){
-  var req = this.req;
-  var next = req.next;
+res.format = function (obj) {
+  const req = this.req
+  const next = req.next
 
-  var keys = Object.keys(obj)
-    .filter(function (v) { return v !== 'default' })
+  const keys = Object.keys(obj)
+    .filter((v) => { return v !== 'default' })
 
-  var key = keys.length > 0
+  const key = keys.length > 0
     ? req.accepts(keys)
-    : false;
+    : false
 
-  this.vary("Accept");
+  this.vary('Accept')
 
   if (key) {
-    this.set('Content-Type', normalizeType(key).value);
-    obj[key](req, this, next);
+    this.set('Content-Type', normalizeType(key).value)
+    obj[key](req, this, next)
   } else if (obj.default) {
     obj.default(req, this, next)
   } else {
     next(createError(406, {
-      types: normalizeTypes(keys).map(function (o) { return o.value })
+      types: normalizeTypes(keys).map((o) => { return o.value })
     }))
   }
 
-  return this;
-};
+  return this
+}
 
 /**
  * Set _Content-Disposition_ header to _attachment_ with optional `filename`.
@@ -608,15 +606,15 @@ res.format = function(obj){
  * @public
  */
 
-res.attachment = function attachment(filename) {
+res.attachment = function attachment (filename) {
   if (filename) {
-    this.type(extname(filename));
+    this.type(extname(filename))
   }
 
-  this.set('Content-Disposition', contentDisposition(filename));
+  this.set('Content-Disposition', contentDisposition(filename))
 
-  return this;
-};
+  return this
+}
 
 /**
  * Append additional header `field` with value `val`.
@@ -633,19 +631,21 @@ res.attachment = function attachment(filename) {
  * @public
  */
 
-res.append = function append(field, val) {
-  var prev = this.get(field);
-  var value = val;
+res.append = function append (field, val) {
+  const prev = this.get(field)
+  let value = val
 
   if (prev) {
     // concat the new and prev vals
-    value = Array.isArray(prev) ? prev.concat(val)
-      : Array.isArray(val) ? [prev].concat(val)
+    value = Array.isArray(prev)
+      ? prev.concat(val)
+      : Array.isArray(val)
+        ? [prev].concat(val)
         : [prev, val]
   }
 
-  return this.set(field, value);
-};
+  return this.set(field, value)
+}
 
 /**
  * Set header `field` to `val`, or pass
@@ -669,28 +669,28 @@ res.append = function append(field, val) {
  */
 
 res.set =
-res.header = function header(field, val) {
+res.header = function header (field, val) {
   if (arguments.length === 2) {
-    var value = Array.isArray(val)
+    let value = Array.isArray(val)
       ? val.map(String)
-      : String(val);
+      : String(val)
 
     // add charset to content-type
     if (field.toLowerCase() === 'content-type') {
       if (Array.isArray(value)) {
-        throw new TypeError('Content-Type cannot be set to an Array');
+        throw new TypeError('Content-Type cannot be set to an Array')
       }
       value = mime.contentType(value)
     }
 
-    this.setHeader(field, value);
+    this.setHeader(field, value)
   } else {
-    for (var key in field) {
-      this.set(key, field[key]);
+    for (const key in field) {
+      this.set(key, field[key])
     }
   }
-  return this;
-};
+  return this
+}
 
 /**
  * Get value for header `field`.
@@ -700,9 +700,9 @@ res.header = function header(field, val) {
  * @public
  */
 
-res.get = function(field){
-  return this.getHeader(field);
-};
+res.get = function (field) {
+  return this.getHeader(field)
+}
 
 /**
  * Clear cookie `name`.
@@ -713,14 +713,14 @@ res.get = function(field){
  * @public
  */
 
-res.clearCookie = function clearCookie(name, options) {
+res.clearCookie = function clearCookie (name, options) {
   // Force cookie expiration by setting expires to the past
-  const opts = { path: '/', ...options, expires: new Date(1)};
+  const opts = { path: '/', ...options, expires: new Date(1) }
   // ensure maxAge is not passed
   delete opts.maxAge
 
-  return this.cookie(name, '', opts);
-};
+  return this.cookie(name, '', opts)
+}
 
 /**
  * Set cookie `name` to `value`, with the given `options`.
@@ -747,24 +747,24 @@ res.clearCookie = function clearCookie(name, options) {
  */
 
 res.cookie = function (name, value, options) {
-  var opts = { ...options };
-  var secret = this.req.secret;
-  var signed = opts.signed;
+  const opts = { ...options }
+  const secret = this.req.secret
+  const signed = opts.signed
 
   if (signed && !secret) {
-    throw new Error('cookieParser("secret") required for signed cookies');
+    throw new Error('cookieParser("secret") required for signed cookies')
   }
 
-  var val = typeof value === 'object'
+  let val = typeof value === 'object'
     ? 'j:' + JSON.stringify(value)
-    : String(value);
+    : String(value)
 
   if (signed) {
-    val = 's:' + sign(val, secret);
+    val = 's:' + sign(val, secret)
   }
 
   if (opts.maxAge != null) {
-    var maxAge = opts.maxAge - 0
+    const maxAge = opts.maxAge - 0
 
     if (!isNaN(maxAge)) {
       opts.expires = new Date(Date.now() + maxAge)
@@ -773,13 +773,13 @@ res.cookie = function (name, value, options) {
   }
 
   if (opts.path == null) {
-    opts.path = '/';
+    opts.path = '/'
   }
 
-  this.append('Set-Cookie', cookie.serialize(name, String(val), opts));
+  this.append('Set-Cookie', cookie.serialize(name, String(val), opts))
 
-  return this;
-};
+  return this
+}
 
 /**
  * Set the location header to `url`.
@@ -798,9 +798,9 @@ res.cookie = function (name, value, options) {
  * @public
  */
 
-res.location = function location(url) {
-  return this.set('Location', encodeUrl(url));
-};
+res.location = function location (url) {
+  return this.set('Location', encodeUrl(url))
+}
 
 /**
  * Redirect to the given `url` with optional response `status`
@@ -816,10 +816,10 @@ res.location = function location(url) {
  * @public
  */
 
-res.redirect = function redirect(url) {
-  var address = url;
-  var body;
-  var status = 302;
+res.redirect = function redirect (url) {
+  let address = url
+  let body
+  let status = 302
 
   // allow status / url
   if (arguments.length === 2) {
@@ -828,46 +828,46 @@ res.redirect = function redirect(url) {
   }
 
   if (!address) {
-    deprecate('Provide a url argument');
+    deprecate('Provide a url argument')
   }
 
   if (typeof address !== 'string') {
-    deprecate('Url must be a string');
+    deprecate('Url must be a string')
   }
 
   if (typeof status !== 'number') {
-    deprecate('Status must be a number');
+    deprecate('Status must be a number')
   }
 
   // Set location header
-  address = this.location(address).get('Location');
+  address = this.location(address).get('Location')
 
   // Support text/{plain,html} by default
   this.format({
-    text: function(){
+    text: function () {
       body = statuses.message[status] + '. Redirecting to ' + address
     },
 
-    html: function(){
-      var u = escapeHtml(address);
+    html: function () {
+      const u = escapeHtml(address)
       body = '<p>' + statuses.message[status] + '. Redirecting to ' + u + '</p>'
     },
 
-    default: function(){
-      body = '';
+    default: function () {
+      body = ''
     }
-  });
+  })
 
   // Respond
-  this.status(status);
-  this.set('Content-Length', Buffer.byteLength(body));
+  this.status(status)
+  this.set('Content-Length', Buffer.byteLength(body))
 
   if (this.req.method === 'HEAD') {
-    this.end();
+    this.end()
   } else {
-    this.end(body);
+    this.end(body)
   }
-};
+}
 
 /**
  * Add `field` to Vary. If already present in the Vary set, then
@@ -878,11 +878,11 @@ res.redirect = function redirect(url) {
  * @public
  */
 
-res.vary = function(field){
-  vary(this, field);
+res.vary = function (field) {
+  vary(this, field)
 
-  return this;
-};
+  return this
+}
 
 /**
  * Render `view` with the given `options` and optional callback `fn`.
@@ -897,121 +897,121 @@ res.vary = function(field){
  * @public
  */
 
-res.render = function render(view, options, callback) {
-  var app = this.req.app;
-  var done = callback;
-  var opts = options || {};
-  var req = this.req;
-  var self = this;
+res.render = function render (view, options, callback) {
+  const app = this.req.app
+  let done = callback
+  let opts = options || {}
+  const req = this.req
+  const self = this
 
   // support callback function as second arg
   if (typeof options === 'function') {
-    done = options;
-    opts = {};
+    done = options
+    opts = {}
   }
 
   // merge res.locals
-  opts._locals = self.locals;
+  opts._locals = self.locals
 
   // default callback to respond
   done = done || function (err, str) {
-    if (err) return req.next(err);
-    self.send(str);
-  };
+    if (err) return req.next(err)
+    self.send(str)
+  }
 
   // render
-  app.render(view, opts, done);
-};
+  app.render(view, opts, done)
+}
 
 // pipe the send file stream
-function sendfile(res, file, options, callback) {
-  var done = false;
-  var streaming;
+function sendfile (res, file, options, callback) {
+  let done = false
+  let streaming
 
   // request aborted
-  function onaborted() {
-    if (done) return;
-    done = true;
+  function onaborted () {
+    if (done) return
+    done = true
 
-    var err = new Error('Request aborted');
-    err.code = 'ECONNABORTED';
-    callback(err);
+    const err = new Error('Request aborted')
+    err.code = 'ECONNABORTED'
+    callback(err)
   }
 
   // directory
-  function ondirectory() {
-    if (done) return;
-    done = true;
+  function ondirectory () {
+    if (done) return
+    done = true
 
-    var err = new Error('EISDIR, read');
-    err.code = 'EISDIR';
-    callback(err);
+    const err = new Error('EISDIR, read')
+    err.code = 'EISDIR'
+    callback(err)
   }
 
   // errors
-  function onerror(err) {
-    if (done) return;
-    done = true;
-    callback(err);
+  function onerror (err) {
+    if (done) return
+    done = true
+    callback(err)
   }
 
   // ended
-  function onend() {
-    if (done) return;
-    done = true;
-    callback();
+  function onend () {
+    if (done) return
+    done = true
+    callback()
   }
 
   // file
-  function onfile() {
-    streaming = false;
+  function onfile () {
+    streaming = false
   }
 
   // finished
-  function onfinish(err) {
-    if (err && err.code === 'ECONNRESET') return onaborted();
-    if (err) return onerror(err);
-    if (done) return;
+  function onfinish (err) {
+    if (err && err.code === 'ECONNRESET') return onaborted()
+    if (err) return onerror(err)
+    if (done) return
 
-    setImmediate(function () {
+    setImmediate(() => {
       if (streaming !== false && !done) {
-        onaborted();
-        return;
+        onaborted()
+        return
       }
 
-      if (done) return;
-      done = true;
-      callback();
-    });
+      if (done) return
+      done = true
+      callback()
+    })
   }
 
   // streaming
-  function onstream() {
-    streaming = true;
+  function onstream () {
+    streaming = true
   }
 
-  file.on('directory', ondirectory);
-  file.on('end', onend);
-  file.on('error', onerror);
-  file.on('file', onfile);
-  file.on('stream', onstream);
-  onFinished(res, onfinish);
+  file.on('directory', ondirectory)
+  file.on('end', onend)
+  file.on('error', onerror)
+  file.on('file', onfile)
+  file.on('stream', onstream)
+  onFinished(res, onfinish)
 
   if (options.headers) {
     // set headers on successful transfer
-    file.on('headers', function headers(res) {
-      var obj = options.headers;
-      var keys = Object.keys(obj);
+    file.on('headers', (res) => {
+      const obj = options.headers
+      const keys = Object.keys(obj)
 
-      for (var i = 0; i < keys.length; i++) {
-        var k = keys[i];
-        res.setHeader(k, obj[k]);
+      for (let i = 0; i < keys.length; i++) {
+        const k = keys[i]
+        res.setHeader(k, obj[k])
       }
-    });
+    })
   }
 
   // pipe
-  file.pipe(res);
+  file.pipe(res)
 }
 
 /**
@@ -1029,12 +1029,12 @@ function sendfile(res, file, options, callback) {
 function stringify (value, replacer, spaces, escape) {
   // v8 checks arguments.length for optimizing simple call
   // https://bugs.chromium.org/p/v8/issues/detail?id=4730
-  var json = replacer || spaces
+  let json = replacer || spaces
     ? JSON.stringify(value, replacer, spaces)
-    : JSON.stringify(value);
+    : JSON.stringify(value)
 
   if (escape && typeof json === 'string') {
-    json = json.replace(/[<>&]/g, function (c) {
+    json = json.replace(/[<>&]/g, (c) => {
       switch (c.charCodeAt(0)) {
         case 0x3c:
           return '\\u003c'
diff --git a/lib/utils.js b/lib/utils.js
index 4f21e7ef1e3..0a60f7531db 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -5,28 +5,27 @@
  * MIT Licensed
  */
 
-'use strict';
+'use strict'
 
 /**
  * Module dependencies.
  * @api private
  */
 
-var { METHODS } = require('node:http');
-var contentType = require('content-type');
-var etag = require('etag');
-var mime = require('mime-types')
-var proxyaddr = require('proxy-addr');
-var qs = require('qs');
-var querystring = require('node:querystring');
-const { Buffer } = require('node:buffer');
-
+const { METHODS } = require('node:http')
+const contentType = require('content-type')
+const etag = require('etag')
+const mime = require('mime-types')
+const proxyaddr = require('proxy-addr')
+const qs = require('qs')
+const querystring = require('node:querystring')
+const { Buffer } = require('node:buffer')
 
 /**
  * A list of lowercased HTTP methods that are supported by Node.js.
  * @api private
  */
-exports.methods = METHODS.map((method) => method.toLowerCase());
+exports.methods = METHODS.map((method) => method.toLowerCase())
 
 /**
  * Return strong ETag for `body`.
@@ -58,11 +57,11 @@ exports.wetag = createETagGenerator({ weak: true })
  * @api private
  */
 
-exports.normalizeType = function(type){
+exports.normalizeType = function (type) {
   return ~type.indexOf('/')
     ? acceptParams(type)
     : { value: (mime.lookup(type) || 'application/octet-stream'), params: {} }
-};
+}
 
 /**
  * Normalize `types`, for example "html" becomes "text/html".
@@ -72,10 +71,9 @@ exports.normalizeType = function(type){
  * @api private
  */
 
-exports.normalizeTypes = function(types) {
-  return types.map(exports.normalizeType);
-};
-
+exports.normalizeTypes = function (types) {
+  return types.map(exports.normalizeType)
+}
 
 /**
  * Parse accept params `str` returning an
@@ -87,36 +85,36 @@ exports.normalizeTypes = function(types) {
  */
 
 function acceptParams (str) {
-  var length = str.length;
-  var colonIndex = str.indexOf(';');
-  var index = colonIndex === -1 ? length : colonIndex;
-  var ret = { value: str.slice(0, index).trim(), quality: 1, params: {} };
+  const length = str.length
+  let colonIndex = str.indexOf(';')
+  let index = colonIndex === -1 ? length : colonIndex
+  const ret = { value: str.slice(0, index).trim(), quality: 1, params: {} }
 
   while (index < length) {
-    var splitIndex = str.indexOf('=', index);
-    if (splitIndex === -1) break;
+    const splitIndex = str.indexOf('=', index)
+    if (splitIndex === -1) break
 
-    var colonIndex = str.indexOf(';', index);
-    var endIndex = colonIndex === -1 ? length : colonIndex;
+    colonIndex = str.indexOf(';', index)
+    const endIndex = colonIndex === -1 ? length : colonIndex
 
     if (splitIndex > endIndex) {
-      index = str.lastIndexOf(';', splitIndex - 1) + 1;
-      continue;
+      index = str.lastIndexOf(';', splitIndex - 1) + 1
+      continue
     }
 
-    var key = str.slice(index, splitIndex).trim();
-    var value = str.slice(splitIndex + 1, endIndex).trim();
+    const key = str.slice(index, splitIndex).trim()
+    const value = str.slice(splitIndex + 1, endIndex).trim()
 
     if (key === 'q') {
-      ret.quality = parseFloat(value);
+      ret.quality = parseFloat(value)
     } else {
-      ret.params[key] = value;
+      ret.params[key] = value
     }
 
-    index = endIndex + 1;
+    index = endIndex + 1
   }
 
-  return ret;
+  return ret
 }
 
 /**
@@ -127,28 +125,28 @@ function acceptParams (str) {
  * @api private
  */
 
-exports.compileETag = function(val) {
-  var fn;
+exports.compileETag = function (val) {
+  let fn
 
   if (typeof val === 'function') {
-    return val;
+    return val
   }
 
   switch (val) {
     case true:
     case 'weak':
-      fn = exports.wetag;
-      break;
+      fn = exports.wetag
+      break
     case false:
-      break;
+      break
     case 'strong':
-      fn = exports.etag;
-      break;
+      fn = exports.etag
+      break
     default:
-      throw new TypeError('unknown value for etag function: ' + val);
+      throw new TypeError('unknown value for etag function: ' + val)
   }
 
-  return fn;
+  return fn
 }
 
 /**
@@ -159,28 +157,28 @@ exports.compileETag = function(val) {
  * @api private
  */
 
-exports.compileQueryParser = function compileQueryParser(val) {
-  var fn;
+exports.compileQueryParser = function compileQueryParser (val) {
+  let fn
 
   if (typeof val === 'function') {
-    return val;
+    return val
   }
 
   switch (val) {
     case true:
     case 'simple':
-      fn = querystring.parse;
-      break;
+      fn = querystring.parse
+      break
     case false:
-      break;
+      break
     case 'extended':
-      fn = parseExtendedQueryString;
-      break;
+      fn = parseExtendedQueryString
+      break
     default:
-      throw new TypeError('unknown value for query parser function: ' + val);
+      throw new TypeError('unknown value for query parser function: ' + val)
   }
 
-  return fn;
+  return fn
 }
 
 /**
@@ -191,26 +189,26 @@ exports.compileQueryParser = function compileQueryParser(val) {
  * @api private
  */
 
-exports.compileTrust = function(val) {
-  if (typeof val === 'function') return val;
+exports.compileTrust = function (val) {
+  if (typeof val === 'function') return val
 
   if (val === true) {
     // Support plain true/false
-    return function(){ return true };
+    return function () { return true }
   }
 
   if (typeof val === 'number') {
     // Support trusting hop count
-    return function(a, i){ return i < val };
+    return function (a, i) { return i < val }
   }
 
   if (typeof val === 'string') {
     // Support comma-separated values
     val = val.split(',')
-      .map(function (v) { return v.trim() })
+      .map((v) => v.trim())
   }
 
-  return proxyaddr.compile(val || []);
+  return proxyaddr.compile(val || [])
 }
 
 /**
@@ -222,20 +220,20 @@ exports.compileTrust = function(val) {
  * @api private
  */
 
-exports.setCharset = function setCharset(type, charset) {
+exports.setCharset = function setCharset (type, charset) {
   if (!type || !charset) {
-    return type;
+    return type
   }
 
   // parse type
-  var parsed = contentType.parse(type);
+  const parsed = contentType.parse(type)
 
   // set charset
-  parsed.parameters.charset = charset;
+  parsed.parameters.charset = charset
 
   // format type
-  return contentType.format(parsed);
-};
+  return contentType.format(parsed)
+}
 
 /**
  * Create an ETag generator function, generating ETags with
@@ -248,7 +246,7 @@ exports.setCharset = function setCharset(type, charset) {
 
 function createETagGenerator (options) {
   return function generateETag (body, encoding) {
-    var buf = !Buffer.isBuffer(body)
+    const buf = !Buffer.isBuffer(body)
       ? Buffer.from(body, encoding)
       : body
 
@@ -264,8 +262,8 @@ function createETagGenerator (options) {
  * @private
  */
 
-function parseExtendedQueryString(str) {
+function parseExtendedQueryString (str) {
   return qs.parse(str, {
     allowPrototypes: true
-  });
+  })
 }
diff --git a/lib/view.js b/lib/view.js
index d66b4a2d89c..383da24fc7a 100644
--- a/lib/view.js
+++ b/lib/view.js
@@ -6,34 +6,34 @@
  * MIT Licensed
  */
 
-'use strict';
+'use strict'
 
 /**
  * Module dependencies.
  * @private
  */
 
-var debug = require('debug')('express:view');
-var path = require('node:path');
-var fs = require('node:fs');
+const debug = require('debug')('express:view')
+const path = require('node:path')
+const fs = require('node:fs')
 
 /**
  * Module variables.
  * @private
  */
 
-var dirname = path.dirname;
-var basename = path.basename;
-var extname = path.extname;
-var join = path.join;
-var resolve = path.resolve;
+const dirname = path.dirname
+const basename = path.basename
+const extname = path.extname
+const join = path.join
+const resolve = path.resolve
 
 /**
  * Module exports.
  * @public
  */
 
-module.exports = View;
+module.exports = View
 
 /**
  * Initialize a new `View` with the given `name`.
@@ -49,36 +49,37 @@ module.exports = View;
  * @public
  */
 
-function View(name, options) {
-  var opts = options || {};
+function View (name, options) {
+  const opts = options || {}
 
-  this.defaultEngine = opts.defaultEngine;
-  this.ext = extname(name);
-  this.name = name;
-  this.root = opts.root;
+  this.defaultEngine = opts.defaultEngine
+  this.ext = extname(name)
+  this.name = name
+  this.root = opts.root
 
   if (!this.ext && !this.defaultEngine) {
-    throw new Error('No default engine was specified and no extension was provided.');
+    throw new Error('No default engine was specified and no extension was provided.')
   }
 
-  var fileName = name;
+  let fileName = name
 
   if (!this.ext) {
     // get extension from default engine name
     this.ext = this.defaultEngine[0] !== '.'
       ? '.' + this.defaultEngine
-      : this.defaultEngine;
+      : this.defaultEngine
 
-    fileName += this.ext;
+    fileName += this.ext
   }
 
   if (!opts.engines[this.ext]) {
     // load engine
-    var mod = this.ext.slice(1)
+    const mod = this.ext.slice(1)
     debug('require "%s"', mod)
 
     // default engine export
-    var fn = require(mod).__express
+    // eslint-disable-next-line global-require
+    const fn = require(mod).__express
 
     if (typeof fn !== 'function') {
       throw new Error('Module "' + mod + '" does not provide a view engine.')
@@ -88,10 +89,10 @@ function View(name, options) {
   }
 
   // store loaded engine
-  this.engine = opts.engines[this.ext];
+  this.engine = opts.engines[this.ext]
 
   // lookup path
-  this.path = this.lookup(fileName);
+  this.path = this.lookup(fileName)
 }
 
 /**
@@ -101,26 +102,26 @@ function View(name, options) {
  * @private
  */
 
-View.prototype.lookup = function lookup(name) {
-  var path;
-  var roots = [].concat(this.root);
+View.prototype.lookup = function lookup (name) {
+  let path
+  const roots = [].concat(this.root)
 
-  debug('lookup "%s"', name);
+  debug('lookup "%s"', name)
 
-  for (var i = 0; i < roots.length && !path; i++) {
-    var root = roots[i];
+  for (let i = 0; i < roots.length && !path; i++) {
+    const root = roots[i]
 
     // resolve the path
-    var loc = resolve(root, name);
-    var dir = dirname(loc);
-    var file = basename(loc);
+    const loc = resolve(root, name)
+    const dir = dirname(loc)
+    const file = basename(loc)
 
     // resolve the file
-    path = this.resolve(dir, file);
+    path = this.resolve(dir, file)
   }
 
-  return path;
-};
+  return path
+}
 
 /**
  * Render with the given options.
@@ -130,33 +131,33 @@ View.prototype.lookup = function lookup(name) {
  * @private
  */
 
-View.prototype.render = function render(options, callback) {
-  var sync = true;
+View.prototype.render = function render (options, callback) {
+  let sync = true
 
-  debug('render "%s"', this.path);
+  debug('render "%s"', this.path)
 
   // render, normalizing sync callbacks
-  this.engine(this.path, options, function onRender() {
+  this.engine(this.path, options, function onRender () {
     if (!sync) {
-      return callback.apply(this, arguments);
+      return callback.apply(this, arguments)
     }
 
     // copy arguments
-    var args = new Array(arguments.length);
-    var cntx = this;
+    const args = new Array(arguments.length)
+    const cntx = this
 
-    for (var i = 0; i < arguments.length; i++) {
-      args[i] = arguments[i];
+    for (let i = 0; i < arguments.length; i++) {
+      args[i] = arguments[i]
     }
 
     // force callback to be async
-    return process.nextTick(function renderTick() {
-      return callback.apply(cntx, args);
-    });
-  });
+    return process.nextTick(function renderTick () {
+      return callback.apply(cntx, args)
+    })
+  })
 
-  sync = false;
-};
+  sync = false
+}
 
 /**
  * Resolve the file within the given directory.
@@ -166,25 +167,25 @@ View.prototype.render = function render(options, callback) {
  * @private
  */
 
-View.prototype.resolve = function resolve(dir, file) {
-  var ext = this.ext;
+View.prototype.resolve = function resolve (dir, file) {
+  const ext = this.ext
 
   // <path>.<ext>
-  var path = join(dir, file);
-  var stat = tryStat(path);
+  let path = join(dir, file)
+  let stat = tryStat(path)
 
   if (stat && stat.isFile()) {
-    return path;
+    return path
   }
 
   // <path>/index.<ext>
-  path = join(dir, basename(file, ext), 'index' + ext);
-  stat = tryStat(path);
+  path = join(dir, basename(file, ext), 'index' + ext)
+  stat = tryStat(path)
 
   if (stat && stat.isFile()) {
-    return path;
+    return path
   }
-};
+}
 
 /**
  * Return a stat, maybe.
@@ -194,12 +195,12 @@ View.prototype.resolve = function resolve(dir, file) {
  * @private
  */
 
-function tryStat(path) {
-  debug('stat "%s"', path);
+function tryStat (path) {
+  debug('stat "%s"', path)
 
   try {
-    return fs.statSync(path);
+    return fs.statSync(path)
   } catch (e) {
-    return undefined;
+    return undefined
   }
 }
diff --git a/package.json b/package.json
index db7661de46d..6b730126508 100644
--- a/package.json
+++ b/package.json
@@ -48,6 +48,7 @@
     "http-errors": "^2.0.0",
     "merge-descriptors": "^2.0.0",
     "mime-types": "^3.0.0",
+    "neostandard": "^0.12.2",
     "on-finished": "^2.4.1",
     "once": "^1.4.0",
     "parseurl": "^1.3.3",
@@ -67,7 +68,7 @@
     "cookie-parser": "1.4.7",
     "cookie-session": "2.1.1",
     "ejs": "^3.1.10",
-    "eslint": "8.47.0",
+    "eslint": "9.39.1",
     "express-session": "^1.18.1",
     "hbs": "4.2.0",
     "marked": "^15.0.3",
diff --git a/test/Route.js b/test/Route.js
index e4b73c7e6ec..d3b137314c4 100644
--- a/test/Route.js
+++ b/test/Route.js
@@ -1,42 +1,41 @@
 'use strict'
 
-var after = require('after');
-var assert = require('node:assert')
-var express = require('../')
-  , Route = express.Route
-  , methods = require('../lib/utils').methods
-
-describe('Route', function(){
-  it('should work without handlers', function(done) {
-    var req = { method: 'GET', url: '/' }
-    var route = new Route('/foo')
+const after = require('after')
+const assert = require('node:assert')
+const { Route } = require('../')
+const { methods } = require('../lib/utils')
+
+describe('Route', () => {
+  it('should work without handlers', (done) => {
+    const req = { method: 'GET', url: '/' }
+    const route = new Route('/foo')
     route.dispatch(req, {}, done)
   })
 
   it('should not stack overflow with a large sync stack', function (done) {
     this.timeout(5000) // long-running test
 
-    var req = { method: 'GET', url: '/' }
-    var route = new Route('/foo')
+    const req = { method: 'GET', url: '/' }
+    const route = new Route('/foo')
 
-    route.get(function (req, res, next) {
+    route.get((req, res, next) => {
       req.counter = 0
       next()
     })
 
-    for (var i = 0; i < 6000; i++) {
-      route.all(function (req, res, next) {
+    for (let i = 0; i < 6000; i++) {
+      route.all((req, res, next) => {
         req.counter++
         next()
       })
     }
 
-    route.get(function (req, res, next) {
+    route.get((req, res, next) => {
       req.called = true
       next()
     })
 
-    route.dispatch(req, {}, function (err) {
+    route.dispatch(req, {}, (err) => {
       if (err) return done(err)
       assert.ok(req.called)
       assert.strictEqual(req.counter, 6000)
@@ -44,231 +43,231 @@ describe('Route', function(){
     })
   })
 
-  describe('.all', function(){
-    it('should add handler', function(done){
-      var req = { method: 'GET', url: '/' };
-      var route = new Route('/foo');
+  describe('.all', () => {
+    it('should add handler', (done) => {
+      const req = { method: 'GET', url: '/' }
+      const route = new Route('/foo')
 
-      route.all(function(req, res, next) {
-        req.called = true;
-        next();
-      });
+      route.all((req, res, next) => {
+        req.called = true
+        next()
+      })
 
-      route.dispatch(req, {}, function (err) {
-        if (err) return done(err);
+      route.dispatch(req, {}, (err) => {
+        if (err) return done(err)
         assert.ok(req.called)
-        done();
-      });
+        done()
+      })
     })
 
-    it('should handle VERBS', function(done) {
-      var count = 0;
-      var route = new Route('/foo');
-      var cb = after(methods.length, function (err) {
-        if (err) return done(err);
+    it('should handle VERBS', (done) => {
+      let count = 0
+      const route = new Route('/foo')
+      const cb = after(methods.length, (err) => {
+        if (err) return done(err)
         assert.strictEqual(count, methods.length)
-        done();
-      });
-
-      route.all(function(req, res, next) {
-        count++;
-        next();
-      });
-
-      methods.forEach(function testMethod(method) {
-        var req = { method: method, url: '/' };
-        route.dispatch(req, {}, cb);
-      });
+        done()
+      })
+
+      route.all((req, res, next) => {
+        count++
+        next()
+      })
+
+      methods.forEach((method) => {
+        const req = { method, url: '/' }
+        route.dispatch(req, {}, cb)
+      })
     })
 
-    it('should stack', function(done) {
-      var req = { count: 0, method: 'GET', url: '/' };
-      var route = new Route('/foo');
+    it('should stack', (done) => {
+      const req = { count: 0, method: 'GET', url: '/' }
+      const route = new Route('/foo')
 
-      route.all(function(req, res, next) {
-        req.count++;
-        next();
-      });
+      route.all((req, res, next) => {
+        req.count++
+        next()
+      })
 
-      route.all(function(req, res, next) {
-        req.count++;
-        next();
-      });
+      route.all((req, res, next) => {
+        req.count++
+        next()
+      })
 
-      route.dispatch(req, {}, function (err) {
-        if (err) return done(err);
+      route.dispatch(req, {}, (err) => {
+        if (err) return done(err)
         assert.strictEqual(req.count, 2)
-        done();
-      });
+        done()
+      })
     })
   })
 
-  describe('.VERB', function(){
-    it('should support .get', function(done){
-      var req = { method: 'GET', url: '/' };
-      var route = new Route('');
+  describe('.VERB', () => {
+    it('should support .get', (done) => {
+      const req = { method: 'GET', url: '/' }
+      const route = new Route('')
 
-      route.get(function(req, res, next) {
-        req.called = true;
-        next();
+      route.get((req, res, next) => {
+        req.called = true
+        next()
       })
 
-      route.dispatch(req, {}, function (err) {
-        if (err) return done(err);
+      route.dispatch(req, {}, (err) => {
+        if (err) return done(err)
         assert.ok(req.called)
-        done();
-      });
+        done()
+      })
     })
 
-    it('should limit to just .VERB', function(done){
-      var req = { method: 'POST', url: '/' };
-      var route = new Route('');
+    it('should limit to just .VERB', (done) => {
+      const req = { method: 'POST', url: '/' }
+      const route = new Route('')
 
-      route.get(function () {
-        throw new Error('not me!');
+      route.get(() => {
+        throw new Error('not me!')
       })
 
-      route.post(function(req, res, next) {
-        req.called = true;
-        next();
+      route.post((req, res, next) => {
+        req.called = true
+        next()
       })
 
-      route.dispatch(req, {}, function (err) {
-        if (err) return done(err);
+      route.dispatch(req, {}, (err) => {
+        if (err) return done(err)
         assert.ok(req.called)
-        done();
-      });
+        done()
+      })
     })
 
-    it('should allow fallthrough', function(done){
-      var req = { order: '', method: 'GET', url: '/' };
-      var route = new Route('');
+    it('should allow fallthrough', (done) => {
+      const req = { order: '', method: 'GET', url: '/' }
+      const route = new Route('')
 
-      route.get(function(req, res, next) {
-        req.order += 'a';
-        next();
+      route.get((req, res, next) => {
+        req.order += 'a'
+        next()
       })
 
-      route.all(function(req, res, next) {
-        req.order += 'b';
-        next();
-      });
+      route.all((req, res, next) => {
+        req.order += 'b'
+        next()
+      })
 
-      route.get(function(req, res, next) {
-        req.order += 'c';
-        next();
+      route.get((req, res, next) => {
+        req.order += 'c'
+        next()
       })
 
-      route.dispatch(req, {}, function (err) {
-        if (err) return done(err);
+      route.dispatch(req, {}, (err) => {
+        if (err) return done(err)
         assert.strictEqual(req.order, 'abc')
-        done();
-      });
+        done()
+      })
     })
   })
 
-  describe('errors', function(){
-    it('should handle errors via arity 4 functions', function(done){
-      var req = { order: '', method: 'GET', url: '/' };
-      var route = new Route('');
+  describe('errors', () => {
+    it('should handle errors via arity 4 functions', (done) => {
+      const req = { order: '', method: 'GET', url: '/' }
+      const route = new Route('')
 
-      route.all(function(req, res, next){
-        next(new Error('foobar'));
-      });
+      route.all((req, res, next) => {
+        next(new Error('foobar'))
+      })
 
-      route.all(function(req, res, next){
-        req.order += '0';
-        next();
-      });
+      route.all((req, res, next) => {
+        req.order += '0'
+        next()
+      })
 
-      route.all(function(err, req, res, next){
-        req.order += 'a';
-        next(err);
-      });
+      route.all((err, req, res, next) => {
+        req.order += 'a'
+        next(err)
+      })
 
-      route.dispatch(req, {}, function (err) {
+      route.dispatch(req, {}, (err) => {
         assert.ok(err)
         assert.strictEqual(err.message, 'foobar')
         assert.strictEqual(req.order, 'a')
-        done();
-      });
+        done()
+      })
     })
 
-    it('should handle throw', function(done) {
-      var req = { order: '', method: 'GET', url: '/' };
-      var route = new Route('');
+    it('should handle throw', (done) => {
+      const req = { order: '', method: 'GET', url: '/' }
+      const route = new Route('')
 
-      route.all(function () {
-        throw new Error('foobar');
-      });
+      route.all(() => {
+        throw new Error('foobar')
+      })
 
-      route.all(function(req, res, next){
-        req.order += '0';
-        next();
-      });
+      route.all((req, res, next) => {
+        req.order += '0'
+        next()
+      })
 
-      route.all(function(err, req, res, next){
-        req.order += 'a';
-        next(err);
-      });
+      route.all((err, req, res, next) => {
+        req.order += 'a'
+        next(err)
+      })
 
-      route.dispatch(req, {}, function (err) {
+      route.dispatch(req, {}, (err) => {
         assert.ok(err)
         assert.strictEqual(err.message, 'foobar')
         assert.strictEqual(req.order, 'a')
-        done();
-      });
-    });
+        done()
+      })
+    })
 
-    it('should handle throwing inside error handlers', function(done) {
-      var req = { method: 'GET', url: '/' };
-      var route = new Route('');
+    it('should handle throwing inside error handlers', (done) => {
+      const req = { method: 'GET', url: '/' }
+      const route = new Route('')
 
-      route.get(function () {
-        throw new Error('boom!');
-      });
+      route.get(() => {
+        throw new Error('boom!')
+      })
 
-      route.get(function(err, req, res, next){
-        throw new Error('oops');
-      });
+      route.get((err, req, res, next) => {
+        throw new Error('oops')
+      })
 
-      route.get(function(err, req, res, next){
-        req.message = err.message;
-        next();
-      });
+      route.get((err, req, res, next) => {
+        req.message = err.message
+        next()
+      })
 
-      route.dispatch(req, {}, function (err) {
-        if (err) return done(err);
+      route.dispatch(req, {}, (err) => {
+        if (err) return done(err)
         assert.strictEqual(req.message, 'oops')
-        done();
-      });
-    });
+        done()
+      })
+    })
 
-    it('should handle throw in .all', function(done) {
-      var req = { method: 'GET', url: '/' };
-      var route = new Route('');
+    it('should handle throw in .all', (done) => {
+      const req = { method: 'GET', url: '/' }
+      const route = new Route('')
 
-      route.all(function(req, res, next){
-        throw new Error('boom!');
-      });
+      route.all((req, res, next) => {
+        throw new Error('boom!')
+      })
 
-      route.dispatch(req, {}, function(err){
+      route.dispatch(req, {}, (err) => {
         assert.ok(err)
         assert.strictEqual(err.message, 'boom!')
-        done();
-      });
-    });
+        done()
+      })
+    })
 
-    it('should handle single error handler', function(done) {
-      var req = { method: 'GET', url: '/' };
-      var route = new Route('');
+    it('should handle single error handler', (done) => {
+      const req = { method: 'GET', url: '/' }
+      const route = new Route('')
 
-      route.all(function(err, req, res, next){
+      route.all((err, req, res, next) => {
         // this should not execute
         throw new Error('should not be called')
-      });
+      })
 
-      route.dispatch(req, {}, done);
-    });
+      route.dispatch(req, {}, done)
+    })
   })
 })
diff --git a/test/Router.js b/test/Router.js
index 7bac7159b04..1e57925d9c6 100644
--- a/test/Router.js
+++ b/test/Router.js
@@ -1,86 +1,85 @@
 'use strict'
 
-var after = require('after');
-var express = require('../')
-  , Router = express.Router
-  , methods = require('../lib/utils').methods
-  , assert = require('node:assert');
-
-describe('Router', function () {
-  it('should return a function with router methods', function () {
-    var router = new Router();
+const after = require('after')
+const { Router } = require('../')
+const { methods } = require('../lib/utils')
+const assert = require('node:assert')
+
+describe('Router', () => {
+  it('should return a function with router methods', () => {
+    const router = new Router()
     assert(typeof router === 'function')
 
     assert(typeof router.get === 'function')
     assert(typeof router.handle === 'function')
     assert(typeof router.use === 'function')
-  });
+  })
 
-  it('should support .use of other routers', function (done) {
-    var router = new Router();
-    var another = new Router();
+  it('should support .use of other routers', (done) => {
+    const router = new Router()
+    const another = new Router()
 
-    another.get('/bar', function (req, res) {
-      res.end();
-    });
-    router.use('/foo', another);
+    another.get('/bar', (req, res) => {
+      res.end()
+    })
+    router.use('/foo', another)
 
-    router.handle({ url: '/foo/bar', method: 'GET' }, { end: done }, function () { });
-  });
+    router.handle({ url: '/foo/bar', method: 'GET' }, { end: done }, () => { })
+  })
 
-  it('should support dynamic routes', function (done) {
-    var router = new Router();
-    var another = new Router();
+  it('should support dynamic routes', (done) => {
+    const router = new Router()
+    const another = new Router()
 
-    another.get('/:bar', function (req, res) {
+    another.get('/:bar', (req, res) => {
       assert.strictEqual(req.params.bar, 'route')
-      res.end();
-    });
-    router.use('/:foo', another);
+      res.end()
+    })
+    router.use('/:foo', another)
 
-    router.handle({ url: '/test/route', method: 'GET' }, { end: done }, function () { });
-  });
+    router.handle({ url: '/test/route', method: 'GET' }, { end: done }, () => { })
+  })
 
-  it('should handle blank URL', function (done) {
-    var router = new Router();
+  it('should handle blank URL', (done) => {
+    const router = new Router()
 
-    router.use(function (req, res) {
+    router.use((req, res) => {
       throw new Error('should not be called')
-    });
+    })
 
-    router.handle({ url: '', method: 'GET' }, {}, done);
-  });
+    router.handle({ url: '', method: 'GET' }, {}, done)
+  })
 
-  it('should handle missing URL', function (done) {
-    var router = new Router()
+  it('should handle missing URL', (done) => {
+    const router = new Router()
 
-    router.use(function (req, res) {
+    router.use((req, res) => {
       throw new Error('should not be called')
     })
 
     router.handle({ method: 'GET' }, {}, done)
   })
 
-  it('handle missing method', function (done) {
-    var all = false
-    var router = new Router()
-    var route = router.route('/foo')
-    var use = false
+  it('handle missing method', (done) => {
+    let all = false
+    const router = new Router()
+    const route = router.route('/foo')
+    let use = false
 
-    route.post(function (req, res, next) { next(new Error('should not run')) })
-    route.all(function (req, res, next) {
+    route.post((req, res, next) => { next(new Error('should not run')) })
+    route.all((req, res, next) => {
       all = true
       next()
     })
-    route.get(function (req, res, next) { next(new Error('should not run')) })
+    route.get((req, res, next) => { next(new Error('should not run')) })
 
-    router.get('/foo', function (req, res, next) { next(new Error('should not run')) })
-    router.use(function (req, res, next) {
+    router.get('/foo', (req, res, next) => { next(new Error('should not run')) })
+    router.use((req, res, next) => {
       use = true
       next()
     })
 
-    router.handle({ url: '/foo' }, {}, function (err) {
+    router.handle({ url: '/foo' }, {}, (err) => {
       if (err) return done(err)
       assert.ok(all)
       assert.ok(use)
@@ -91,380 +90,380 @@ describe('Router', function () {
   it('should not stack overflow with many registered routes', function (done) {
     this.timeout(5000) // long-running test
 
-    var handler = function (req, res) { res.end(new Error('wrong handler')) };
-    var router = new Router();
+    const handler = function (req, res) { res.end(new Error('wrong handler')) }
+    const router = new Router()
 
-    for (var i = 0; i < 6000; i++) {
+    for (let i = 0; i < 6000; i++) {
       router.get('/thing' + i, handler)
     }
 
-    router.get('/', function (req, res) {
-      res.end();
-    });
+    router.get('/', (req, res) => {
+      res.end()
+    })
 
-    router.handle({ url: '/', method: 'GET' }, { end: done }, function () { });
-  });
+    router.handle({ url: '/', method: 'GET' }, { end: done }, () => { })
+  })
 
   it('should not stack overflow with a large sync route stack', function (done) {
     this.timeout(5000) // long-running test
 
-    var router = new Router()
+    const router = new Router()
 
-    router.get('/foo', function (req, res, next) {
+    router.get('/foo', (req, res, next) => {
       req.counter = 0
       next()
     })
 
-    for (var i = 0; i < 6000; i++) {
-      router.get('/foo', function (req, res, next) {
+    for (let i = 0; i < 6000; i++) {
+      router.get('/foo', (req, res, next) => {
         req.counter++
         next()
       })
     }
 
-    router.get('/foo', function (req, res) {
+    router.get('/foo', (req, res) => {
       assert.strictEqual(req.counter, 6000)
       res.end()
     })
 
-    router.handle({ url: '/foo', method: 'GET' }, { end: done }, function (err) {
-      assert(!err, err);
-    });
+    router.handle({ url: '/foo', method: 'GET' }, { end: done }, (err) => {
+      assert(!err, err)
+    })
   })
 
   it('should not stack overflow with a large sync middleware stack', function (done) {
     this.timeout(5000) // long-running test
 
-    var router = new Router()
+    const router = new Router()
 
-    router.use(function (req, res, next) {
+    router.use((req, res, next) => {
       req.counter = 0
       next()
     })
 
-    for (var i = 0; i < 6000; i++) {
-      router.use(function (req, res, next) {
+    for (let i = 0; i < 6000; i++) {
+      router.use((req, res, next) => {
         req.counter++
         next()
       })
     }
 
-    router.use(function (req, res) {
+    router.use((req, res) => {
       assert.strictEqual(req.counter, 6000)
       res.end()
     })
 
-    router.handle({ url: '/', method: 'GET' }, { end: done }, function (err) {
-      assert(!err, err);
+    router.handle({ url: '/', method: 'GET' }, { end: done }, (err) => {
+      assert(!err, err)
     })
   })
 
-  describe('.handle', function () {
-    it('should dispatch', function (done) {
-      var router = new Router();
+  describe('.handle', () => {
+    it('should dispatch', (done) => {
+      const router = new Router()
 
-      router.route('/foo').get(function (req, res) {
-        res.send('foo');
-      });
+      router.route('/foo').get((req, res) => {
+        res.send('foo')
+      })
 
-      var res = {
+      const res = {
         send: function (val) {
           assert.strictEqual(val, 'foo')
-          done();
+          done()
         }
       }
-      router.handle({ url: '/foo', method: 'GET' }, res, function () { });
+      router.handle({ url: '/foo', method: 'GET' }, res, () => { })
     })
   })
 
-  describe('.multiple callbacks', function () {
-    it('should throw if a callback is null', function () {
-      assert.throws(function () {
-        var router = new Router();
-        router.route('/foo').all(null);
+  describe('.multiple callbacks', () => {
+    it('should throw if a callback is null', () => {
+      assert.throws(() => {
+        const router = new Router()
+        router.route('/foo').all(null)
       })
     })
 
-    it('should throw if a callback is undefined', function () {
-      assert.throws(function () {
-        var router = new Router();
-        router.route('/foo').all(undefined);
+    it('should throw if a callback is undefined', () => {
+      assert.throws(() => {
+        const router = new Router()
+        router.route('/foo').all(undefined)
       })
     })
 
-    it('should throw if a callback is not a function', function () {
-      assert.throws(function () {
-        var router = new Router();
-        router.route('/foo').all('not a function');
+    it('should throw if a callback is not a function', () => {
+      assert.throws(() => {
+        const router = new Router()
+        router.route('/foo').all('not a function')
       })
     })
 
-    it('should not throw if all callbacks are functions', function () {
-      var router = new Router();
-      router.route('/foo').all(function () { }).all(function () { });
+    it('should not throw if all callbacks are functions', () => {
+      const router = new Router()
+      router.route('/foo').all(() => { }).all(() => { })
     })
   })
 
-  describe('error', function () {
-    it('should skip non error middleware', function (done) {
-      var router = new Router();
+  describe('error', () => {
+    it('should skip non error middleware', (done) => {
+      const router = new Router()
 
-      router.get('/foo', function (req, res, next) {
-        next(new Error('foo'));
-      });
+      router.get('/foo', (req, res, next) => {
+        next(new Error('foo'))
+      })
 
-      router.get('/bar', function (req, res, next) {
-        next(new Error('bar'));
-      });
+      router.get('/bar', (req, res, next) => {
+        next(new Error('bar'))
+      })
 
-      router.use(function (req, res, next) {
-        assert(false);
-      });
+      router.use((req, res, next) => {
+        assert(false)
+      })
 
-      router.use(function (err, req, res, next) {
-        assert.equal(err.message, 'foo');
-        done();
-      });
+      router.use((err, req, res, next) => {
+        assert.equal(err.message, 'foo')
+        done()
+      })
 
-      router.handle({ url: '/foo', method: 'GET' }, {}, done);
-    });
+      router.handle({ url: '/foo', method: 'GET' }, {}, done)
+    })
 
-    it('should handle throwing inside routes with params', function (done) {
-      var router = new Router();
+    it('should handle throwing inside routes with params', (done) => {
+      const router = new Router()
 
-      router.get('/foo/:id', function () {
-        throw new Error('foo');
-      });
+      router.get('/foo/:id', () => {
+        throw new Error('foo')
+      })
 
-      router.use(function (req, res, next) {
-        assert(false);
-      });
+      router.use((req, res, next) => {
+        assert(false)
+      })
 
-      router.use(function (err, req, res, next) {
-        assert.equal(err.message, 'foo');
-        done();
-      });
+      router.use((err, req, res, next) => {
+        assert.equal(err.message, 'foo')
+        done()
+      })
 
-      router.handle({ url: '/foo/2', method: 'GET' }, {}, function () { });
-    });
+      router.handle({ url: '/foo/2', method: 'GET' }, {}, () => { })
+    })
 
-    it('should handle throwing in handler after async param', function (done) {
-      var router = new Router();
+    it('should handle throwing in handler after async param', (done) => {
+      const router = new Router()
 
-      router.param('user', function (req, res, next, val) {
-        process.nextTick(function () {
-          req.user = val;
-          next();
-        });
-      });
+      router.param('user', (req, res, next, val) => {
+        process.nextTick(() => {
+          req.user = val
+          next()
+        })
+      })
 
-      router.use('/:user', function (req, res, next) {
-        throw new Error('oh no!');
-      });
+      router.use('/:user', (req, res, next) => {
+        throw new Error('oh no!')
+      })
 
-      router.use(function (err, req, res, next) {
-        assert.equal(err.message, 'oh no!');
-        done();
-      });
+      router.use((err, req, res, next) => {
+        assert.equal(err.message, 'oh no!')
+        done()
+      })
 
-      router.handle({ url: '/bob', method: 'GET' }, {}, function () { });
-    });
+      router.handle({ url: '/bob', method: 'GET' }, {}, () => { })
+    })
 
-    it('should handle throwing inside error handlers', function (done) {
-      var router = new Router();
+    it('should handle throwing inside error handlers', (done) => {
+      const router = new Router()
 
-      router.use(function (req, res, next) {
-        throw new Error('boom!');
-      });
+      router.use((req, res, next) => {
+        throw new Error('boom!')
+      })
 
-      router.use(function (err, req, res, next) {
-        throw new Error('oops');
-      });
+      router.use((err, req, res, next) => {
+        throw new Error('oops')
+      })
 
-      router.use(function (err, req, res, next) {
-        assert.equal(err.message, 'oops');
-        done();
-      });
+      router.use((err, req, res, next) => {
+        assert.equal(err.message, 'oops')
+        done()
+      })
 
-      router.handle({ url: '/', method: 'GET' }, {}, done);
-    });
+      router.handle({ url: '/', method: 'GET' }, {}, done)
+    })
   })
 
-  describe('FQDN', function () {
-    it('should not obscure FQDNs', function (done) {
-      var request = { hit: 0, url: 'http://example.com/foo', method: 'GET' };
-      var router = new Router();
-
-      router.use(function (req, res, next) {
-        assert.equal(req.hit++, 0);
-        assert.equal(req.url, 'http://example.com/foo');
-        next();
-      });
-
-      router.handle(request, {}, function (err) {
-        if (err) return done(err);
-        assert.equal(request.hit, 1);
-        done();
-      });
-    });
-
-    it('should ignore FQDN in search', function (done) {
-      var request = { hit: 0, url: '/proxy?url=http://example.com/blog/post/1', method: 'GET' };
-      var router = new Router();
-
-      router.use('/proxy', function (req, res, next) {
-        assert.equal(req.hit++, 0);
-        assert.equal(req.url, '/?url=http://example.com/blog/post/1');
-        next();
-      });
-
-      router.handle(request, {}, function (err) {
-        if (err) return done(err);
-        assert.equal(request.hit, 1);
-        done();
-      });
-    });
-
-    it('should ignore FQDN in path', function (done) {
-      var request = { hit: 0, url: '/proxy/http://example.com/blog/post/1', method: 'GET' };
-      var router = new Router();
-
-      router.use('/proxy', function (req, res, next) {
-        assert.equal(req.hit++, 0);
-        assert.equal(req.url, '/http://example.com/blog/post/1');
-        next();
-      });
-
-      router.handle(request, {}, function (err) {
-        if (err) return done(err);
-        assert.equal(request.hit, 1);
-        done();
-      });
-    });
-
-    it('should adjust FQDN req.url', function (done) {
-      var request = { hit: 0, url: 'http://example.com/blog/post/1', method: 'GET' };
-      var router = new Router();
-
-      router.use('/blog', function (req, res, next) {
-        assert.equal(req.hit++, 0);
-        assert.equal(req.url, 'http://example.com/post/1');
-        next();
-      });
-
-      router.handle(request, {}, function (err) {
-        if (err) return done(err);
-        assert.equal(request.hit, 1);
-        done();
-      });
-    });
-
-    it('should adjust FQDN req.url with multiple handlers', function (done) {
-      var request = { hit: 0, url: 'http://example.com/blog/post/1', method: 'GET' };
-      var router = new Router();
-
-      router.use(function (req, res, next) {
-        assert.equal(req.hit++, 0);
-        assert.equal(req.url, 'http://example.com/blog/post/1');
-        next();
-      });
-
-      router.use('/blog', function (req, res, next) {
-        assert.equal(req.hit++, 1);
-        assert.equal(req.url, 'http://example.com/post/1');
-        next();
-      });
-
-      router.handle(request, {}, function (err) {
-        if (err) return done(err);
-        assert.equal(request.hit, 2);
-        done();
-      });
-    });
-
-    it('should adjust FQDN req.url with multiple routed handlers', function (done) {
-      var request = { hit: 0, url: 'http://example.com/blog/post/1', method: 'GET' };
-      var router = new Router();
-
-      router.use('/blog', function (req, res, next) {
-        assert.equal(req.hit++, 0);
-        assert.equal(req.url, 'http://example.com/post/1');
-        next();
-      });
-
-      router.use('/blog', function (req, res, next) {
-        assert.equal(req.hit++, 1);
-        assert.equal(req.url, 'http://example.com/post/1');
-        next();
-      });
-
-      router.use(function (req, res, next) {
-        assert.equal(req.hit++, 2);
-        assert.equal(req.url, 'http://example.com/blog/post/1');
-        next();
-      });
-
-      router.handle(request, {}, function (err) {
-        if (err) return done(err);
-        assert.equal(request.hit, 3);
-        done();
-      });
-    });
+  describe('FQDN', () => {
+    it('should not obscure FQDNs', (done) => {
+      const request = { hit: 0, url: 'http://example.com/foo', method: 'GET' }
+      const router = new Router()
+
+      router.use((req, res, next) => {
+        assert.equal(req.hit++, 0)
+        assert.equal(req.url, 'http://example.com/foo')
+        next()
+      })
+
+      router.handle(request, {}, (err) => {
+        if (err) return done(err)
+        assert.equal(request.hit, 1)
+        done()
+      })
+    })
+
+    it('should ignore FQDN in search', (done) => {
+      const request = { hit: 0, url: '/proxy?url=http://example.com/blog/post/1', method: 'GET' }
+      const router = new Router()
+
+      router.use('/proxy', (req, res, next) => {
+        assert.equal(req.hit++, 0)
+        assert.equal(req.url, '/?url=http://example.com/blog/post/1')
+        next()
+      })
+
+      router.handle(request, {}, (err) => {
+        if (err) return done(err)
+        assert.equal(request.hit, 1)
+        done()
+      })
+    })
+
+    it('should ignore FQDN in path', (done) => {
+      const request = { hit: 0, url: '/proxy/http://example.com/blog/post/1', method: 'GET' }
+      const router = new Router()
+
+      router.use('/proxy', (req, res, next) => {
+        assert.equal(req.hit++, 0)
+        assert.equal(req.url, '/http://example.com/blog/post/1')
+        next()
+      })
+
+      router.handle(request, {}, (err) => {
+        if (err) return done(err)
+        assert.equal(request.hit, 1)
+        done()
+      })
+    })
+
+    it('should adjust FQDN req.url', (done) => {
+      const request = { hit: 0, url: 'http://example.com/blog/post/1', method: 'GET' }
+      const router = new Router()
+
+      router.use('/blog', (req, res, next) => {
+        assert.equal(req.hit++, 0)
+        assert.equal(req.url, 'http://example.com/post/1')
+        next()
+      })
+
+      router.handle(request, {}, (err) => {
+        if (err) return done(err)
+        assert.equal(request.hit, 1)
+        done()
+      })
+    })
+
+    it('should adjust FQDN req.url with multiple handlers', (done) => {
+      const request = { hit: 0, url: 'http://example.com/blog/post/1', method: 'GET' }
+      const router = new Router()
+
+      router.use((req, res, next) => {
+        assert.equal(req.hit++, 0)
+        assert.equal(req.url, 'http://example.com/blog/post/1')
+        next()
+      })
+
+      router.use('/blog', (req, res, next) => {
+        assert.equal(req.hit++, 1)
+        assert.equal(req.url, 'http://example.com/post/1')
+        next()
+      })
+
+      router.handle(request, {}, (err) => {
+        if (err) return done(err)
+        assert.equal(request.hit, 2)
+        done()
+      })
+    })
+
+    it('should adjust FQDN req.url with multiple routed handlers', (done) => {
+      const request = { hit: 0, url: 'http://example.com/blog/post/1', method: 'GET' }
+      const router = new Router()
+
+      router.use('/blog', (req, res, next) => {
+        assert.equal(req.hit++, 0)
+        assert.equal(req.url, 'http://example.com/post/1')
+        next()
+      })
+
+      router.use('/blog', (req, res, next) => {
+        assert.equal(req.hit++, 1)
+        assert.equal(req.url, 'http://example.com/post/1')
+        next()
+      })
+
+      router.use((req, res, next) => {
+        assert.equal(req.hit++, 2)
+        assert.equal(req.url, 'http://example.com/blog/post/1')
+        next()
+      })
+
+      router.handle(request, {}, (err) => {
+        if (err) return done(err)
+        assert.equal(request.hit, 3)
+        done()
+      })
+    })
   })
 
-  describe('.all', function () {
-    it('should support using .all to capture all http verbs', function (done) {
-      var router = new Router();
+  describe('.all', () => {
+    it('should support using .all to capture all http verbs', (done) => {
+      const router = new Router()
 
-      var count = 0;
-      router.all('/foo', function () { count++; });
+      let count = 0
+      router.all('/foo', () => { count++ })
 
-      var url = '/foo?bar=baz';
+      const url = '/foo?bar=baz'
 
-      methods.forEach(function testMethod(method) {
-        router.handle({ url: url, method: method }, {}, function () { });
-      });
+      methods.forEach((method) => {
+        router.handle({ url, method }, {}, () => { })
+      })
 
-      assert.equal(count, methods.length);
-      done();
+      assert.equal(count, methods.length)
+      done()
     })
   })
 
-  describe('.use', function () {
-    it('should require middleware', function () {
-      var router = new Router()
-      assert.throws(function () { router.use('/') }, /argument handler is required/)
+  describe('.use', () => {
+    it('should require middleware', () => {
+      const router = new Router()
+      assert.throws(() => { router.use('/') }, /argument handler is required/)
     })
 
-    it('should reject string as middleware', function () {
-      var router = new Router()
-      assert.throws(function () { router.use('/', 'foo') }, /argument handler must be a function/)
+    it('should reject string as middleware', () => {
+      const router = new Router()
+      assert.throws(() => { router.use('/', 'foo') }, /argument handler must be a function/)
     })
 
-    it('should reject number as middleware', function () {
-      var router = new Router()
-      assert.throws(function () { router.use('/', 42) }, /argument handler must be a function/)
+    it('should reject number as middleware', () => {
+      const router = new Router()
+      assert.throws(() => { router.use('/', 42) }, /argument handler must be a function/)
     })
 
-    it('should reject null as middleware', function () {
-      var router = new Router()
-      assert.throws(function () { router.use('/', null) }, /argument handler must be a function/)
+    it('should reject null as middleware', () => {
+      const router = new Router()
+      assert.throws(() => { router.use('/', null) }, /argument handler must be a function/)
     })
 
-    it('should reject Date as middleware', function () {
-      var router = new Router()
-      assert.throws(function () { router.use('/', new Date()) }, /argument handler must be a function/)
+    it('should reject Date as middleware', () => {
+      const router = new Router()
+      assert.throws(() => { router.use('/', new Date()) }, /argument handler must be a function/)
     })
 
-    it('should be called for any URL', function (done) {
-      var cb = after(4, done)
-      var router = new Router()
+    it('should be called for any URL', (done) => {
+      const cb = after(4, done)
+      const router = new Router()
 
-      function no() {
+      function no () {
         throw new Error('should not be called')
       }
 
-      router.use(function (req, res) {
+      router.use((req, res) => {
         res.end()
       })
 
@@ -474,163 +473,162 @@ describe('Router', function () {
       router.handle({ url: '*', method: 'GET' }, { end: cb }, no)
     })
 
-    it('should accept array of middleware', function (done) {
-      var count = 0;
-      var router = new Router();
+    it('should accept array of middleware', (done) => {
+      let count = 0
+      const router = new Router()
 
-      function fn1(req, res, next) {
-        assert.equal(++count, 1);
-        next();
+      function fn1 (req, res, next) {
+        assert.equal(++count, 1)
+        next()
       }
 
-      function fn2(req, res, next) {
-        assert.equal(++count, 2);
-        next();
+      function fn2 (req, res, next) {
+        assert.equal(++count, 2)
+        next()
       }
 
-      router.use([fn1, fn2], function (req, res) {
-        assert.equal(++count, 3);
-        done();
-      });
+      router.use([fn1, fn2], (req, res) => {
+        assert.equal(++count, 3)
+        done()
+      })
 
-      router.handle({ url: '/foo', method: 'GET' }, {}, function () { });
+      router.handle({ url: '/foo', method: 'GET' }, {}, () => { })
     })
   })
 
-  describe('.param', function () {
-    it('should require function', function () {
-      var router = new Router();
-      assert.throws(router.param.bind(router, 'id'), /argument fn is required/);
-    });
-
-    it('should reject non-function', function () {
-      var router = new Router();
-      assert.throws(router.param.bind(router, 'id', 42), /argument fn must be a function/);
-    });
-
-    it('should call param function when routing VERBS', function (done) {
-      var router = new Router();
-
-      router.param('id', function (req, res, next, id) {
-        assert.equal(id, '123');
-        next();
-      });
-
-      router.get('/foo/:id/bar', function (req, res, next) {
-        assert.equal(req.params.id, '123');
-        next();
-      });
-
-      router.handle({ url: '/foo/123/bar', method: 'get' }, {}, done);
-    });
-
-    it('should call param function when routing middleware', function (done) {
-      var router = new Router();
-
-      router.param('id', function (req, res, next, id) {
-        assert.equal(id, '123');
-        next();
-      });
-
-      router.use('/foo/:id/bar', function (req, res, next) {
-        assert.equal(req.params.id, '123');
-        assert.equal(req.url, '/baz');
-        next();
-      });
-
-      router.handle({ url: '/foo/123/bar/baz', method: 'get' }, {}, done);
-    });
-
-    it('should only call once per request', function (done) {
-      var count = 0;
-      var req = { url: '/foo/bob/bar', method: 'get' };
-      var router = new Router();
-      var sub = new Router();
-
-      sub.get('/bar', function (req, res, next) {
-        next();
-      });
-
-      router.param('user', function (req, res, next, user) {
-        count++;
-        req.user = user;
-        next();
-      });
-
-      router.use('/foo/:user/', new Router());
-      router.use('/foo/:user/', sub);
-
-      router.handle(req, {}, function (err) {
-        if (err) return done(err);
-        assert.equal(count, 1);
-        assert.equal(req.user, 'bob');
-        done();
-      });
-    });
-
-    it('should call when values differ', function (done) {
-      var count = 0;
-      var req = { url: '/foo/bob/bar', method: 'get' };
-      var router = new Router();
-      var sub = new Router();
-
-      sub.get('/bar', function (req, res, next) {
-        next();
-      });
-
-      router.param('user', function (req, res, next, user) {
-        count++;
-        req.user = user;
-        next();
-      });
-
-      router.use('/foo/:user/', new Router());
-      router.use('/:user/bob/', sub);
-
-      router.handle(req, {}, function (err) {
-        if (err) return done(err);
-        assert.equal(count, 2);
-        assert.equal(req.user, 'foo');
-        done();
-      });
-    });
-  });
-
-  describe('parallel requests', function () {
-    it('should not mix requests', function (done) {
-      var req1 = { url: '/foo/50/bar', method: 'get' };
-      var req2 = { url: '/foo/10/bar', method: 'get' };
-      var router = new Router();
-      var sub = new Router();
-      var cb = after(2, done)
-
-
-      sub.get('/bar', function (req, res, next) {
-        next();
-      });
-
-      router.param('ms', function (req, res, next, ms) {
-        ms = parseInt(ms, 10);
-        req.ms = ms;
-        setTimeout(next, ms);
-      });
-
-      router.use('/foo/:ms/', new Router());
-      router.use('/foo/:ms/', sub);
-
-      router.handle(req1, {}, function (err) {
-        assert.ifError(err);
-        assert.equal(req1.ms, 50);
-        assert.equal(req1.originalUrl, '/foo/50/bar');
+  describe('.param', () => {
+    it('should require function', () => {
+      const router = new Router()
+      assert.throws(router.param.bind(router, 'id'), /argument fn is required/)
+    })
+
+    it('should reject non-function', () => {
+      const router = new Router()
+      assert.throws(router.param.bind(router, 'id', 42), /argument fn must be a function/)
+    })
+
+    it('should call param function when routing VERBS', (done) => {
+      const router = new Router()
+
+      router.param('id', (req, res, next, id) => {
+        assert.equal(id, '123')
+        next()
+      })
+
+      router.get('/foo/:id/bar', (req, res, next) => {
+        assert.equal(req.params.id, '123')
+        next()
+      })
+
+      router.handle({ url: '/foo/123/bar', method: 'get' }, {}, done)
+    })
+
+    it('should call param function when routing middleware', (done) => {
+      const router = new Router()
+
+      router.param('id', (req, res, next, id) => {
+        assert.equal(id, '123')
+        next()
+      })
+
+      router.use('/foo/:id/bar', (req, res, next) => {
+        assert.equal(req.params.id, '123')
+        assert.equal(req.url, '/baz')
+        next()
+      })
+
+      router.handle({ url: '/foo/123/bar/baz', method: 'get' }, {}, done)
+    })
+
+    it('should only call once per request', (done) => {
+      let count = 0
+      const req = { url: '/foo/bob/bar', method: 'get' }
+      const router = new Router()
+      const sub = new Router()
+
+      sub.get('/bar', (req, res, next) => {
+        next()
+      })
+
+      router.param('user', (req, res, next, user) => {
+        count++
+        req.user = user
+        next()
+      })
+
+      router.use('/foo/:user/', new Router())
+      router.use('/foo/:user/', sub)
+
+      router.handle(req, {}, (err) => {
+        if (err) return done(err)
+        assert.equal(count, 1)
+        assert.equal(req.user, 'bob')
+        done()
+      })
+    })
+
+    it('should call when values differ', (done) => {
+      let count = 0
+      const req = { url: '/foo/bob/bar', method: 'get' }
+      const router = new Router()
+      const sub = new Router()
+
+      sub.get('/bar', (req, res, next) => {
+        next()
+      })
+
+      router.param('user', (req, res, next, user) => {
+        count++
+        req.user = user
+        next()
+      })
+
+      router.use('/foo/:user/', new Router())
+      router.use('/:user/bob/', sub)
+
+      router.handle(req, {}, (err) => {
+        if (err) return done(err)
+        assert.equal(count, 2)
+        assert.equal(req.user, 'foo')
+        done()
+      })
+    })
+  })
+
+  describe('parallel requests', () => {
+    it('should not mix requests', (done) => {
+      const req1 = { url: '/foo/50/bar', method: 'get' }
+      const req2 = { url: '/foo/10/bar', method: 'get' }
+      const router = new Router()
+      const sub = new Router()
+      const cb = after(2, done)
+
+      sub.get('/bar', (req, res, next) => {
+        next()
+      })
+
+      router.param('ms', (req, res, next, ms) => {
+        ms = parseInt(ms, 10)
+        req.ms = ms
+        setTimeout(next, ms)
+      })
+
+      router.use('/foo/:ms/', new Router())
+      router.use('/foo/:ms/', sub)
+
+      router.handle(req1, {}, (err) => {
+        assert.ifError(err)
+        assert.equal(req1.ms, 50)
+        assert.equal(req1.originalUrl, '/foo/50/bar')
         cb()
-      });
+      })
 
-      router.handle(req2, {}, function (err) {
-        assert.ifError(err);
-        assert.equal(req2.ms, 10);
-        assert.equal(req2.originalUrl, '/foo/10/bar');
+      router.handle(req2, {}, (err) => {
+        assert.ifError(err)
+        assert.equal(req2.ms, 10)
+        assert.equal(req2.originalUrl, '/foo/10/bar')
         cb()
-      });
-    });
-  });
+      })
+    })
+  })
 })
diff --git a/test/acceptance/auth.js b/test/acceptance/auth.js
index d7838755a08..1ddd49b48f2 100644
--- a/test/acceptance/auth.js
+++ b/test/acceptance/auth.js
@@ -1,49 +1,49 @@
-var app = require('../../examples/auth')
-var request = require('supertest')
+const app = require('../../examples/auth/')
+const request = require('supertest')
 
-function getCookie(res) {
-  return res.headers['set-cookie'][0].split(';')[0];
+function getCookie (res) {
+  return res.headers['set-cookie'][0].split(';')[0]
 }
 
-describe('auth', function(){
-  describe('GET /',function(){
-    it('should redirect to /login', function(done){
+describe('auth', () => {
+  describe('GET /', () => {
+    it('should redirect to /login', (done) => {
       request(app)
-      .get('/')
-      .expect('Location', '/login')
-      .expect(302, done)
+        .get('/')
+        .expect('Location', '/login')
+        .expect(302, done)
     })
   })
 
-  describe('GET /login',function(){
-    it('should render login form', function(done){
+  describe('GET /login', () => {
+    it('should render login form', (done) => {
       request(app)
-      .get('/login')
-      .expect(200, /<form/, done)
+        .get('/login')
+        .expect(200, /<form/, done)
     })
 
-    it('should display login error for bad user', function (done) {
+    it('should display login error for bad user', (done) => {
       request(app)
-      .post('/login')
-      .type('urlencoded')
-      .send('username=not-tj&password=foobar')
-      .expect('Location', '/login')
-      .expect(302, function(err, res){
-        if (err) return done(err)
-        request(app)
-        .get('/login')
-        .set('Cookie', getCookie(res))
-        .expect(200, /Authentication failed/, done)
-      })
+        .post('/login')
+        .type('urlencoded')
+        .send('username=not-tj&password=foobar')
+        .expect('Location', '/login')
+        .expect(302, (err, res) => {
+          if (err) return done(err)
+          request(app)
+            .get('/login')
+            .set('Cookie', getCookie(res))
+            .expect(200, /Authentication failed/, done)
+        })
     })
 
-    it('should display login error for bad password', function (done) {
+    it('should display login error for bad password', (done) => {
       request(app)
         .post('/login')
         .type('urlencoded')
         .send('username=tj&password=nogood')
         .expect('Location', '/login')
-        .expect(302, function (err, res) {
+        .expect(302, (err, res) => {
           if (err) return done(err)
           request(app)
             .get('/login')
@@ -53,65 +53,65 @@ describe('auth', function(){
     })
   })
 
-  describe('GET /logout',function(){
-    it('should redirect to /', function(done){
+  describe('GET /logout', () => {
+    it('should redirect to /', (done) => {
       request(app)
-      .get('/logout')
-      .expect('Location', '/')
-      .expect(302, done)
+        .get('/logout')
+        .expect('Location', '/')
+        .expect(302, done)
     })
   })
 
-  describe('GET /restricted',function(){
-    it('should redirect to /login without cookie', function(done){
+  describe('GET /restricted', () => {
+    it('should redirect to /login without cookie', (done) => {
       request(app)
-      .get('/restricted')
-      .expect('Location', '/login')
-      .expect(302, done)
+        .get('/restricted')
+        .expect('Location', '/login')
+        .expect(302, done)
     })
 
-    it('should succeed with proper cookie', function(done){
+    it('should succeed with proper cookie', (done) => {
       request(app)
-      .post('/login')
-      .type('urlencoded')
-      .send('username=tj&password=foobar')
-      .expect('Location', '/')
-      .expect(302, function(err, res){
-        if (err) return done(err)
-        request(app)
-        .get('/restricted')
-        .set('Cookie', getCookie(res))
-        .expect(200, done)
-      })
+        .post('/login')
+        .type('urlencoded')
+        .send('username=tj&password=foobar')
+        .expect('Location', '/')
+        .expect(302, (err, res) => {
+          if (err) return done(err)
+          request(app)
+            .get('/restricted')
+            .set('Cookie', getCookie(res))
+            .expect(200, done)
+        })
     })
   })
 
-  describe('POST /login', function(){
-    it('should fail without proper username', function(done){
+  describe('POST /login', () => {
+    it('should fail without proper username', (done) => {
       request(app)
-      .post('/login')
-      .type('urlencoded')
-      .send('username=not-tj&password=foobar')
-      .expect('Location', '/login')
-      .expect(302, done)
+        .post('/login')
+        .type('urlencoded')
+        .send('username=not-tj&password=foobar')
+        .expect('Location', '/login')
+        .expect(302, done)
     })
 
-    it('should fail without proper password', function(done){
+    it('should fail without proper password', (done) => {
       request(app)
-      .post('/login')
-      .type('urlencoded')
-      .send('username=tj&password=baz')
-      .expect('Location', '/login')
-      .expect(302, done)
+        .post('/login')
+        .type('urlencoded')
+        .send('username=tj&password=baz')
+        .expect('Location', '/login')
+        .expect(302, done)
     })
 
-    it('should succeed with proper credentials', function(done){
+    it('should succeed with proper credentials', (done) => {
       request(app)
-      .post('/login')
-      .type('urlencoded')
-      .send('username=tj&password=foobar')
-      .expect('Location', '/')
-      .expect(302, done)
+        .post('/login')
+        .type('urlencoded')
+        .send('username=tj&password=foobar')
+        .expect('Location', '/')
+        .expect(302, done)
     })
   })
 })
diff --git a/test/acceptance/content-negotiation.js b/test/acceptance/content-negotiation.js
index ac9dbaf557e..961f34bfaea 100644
--- a/test/acceptance/content-negotiation.js
+++ b/test/acceptance/content-negotiation.js
@@ -1,49 +1,48 @@
+const request = require('supertest')
+const app = require('../../examples/content-negotiation/')
 
-var request = require('supertest')
-  , app = require('../../examples/content-negotiation');
-
-describe('content-negotiation', function(){
-  describe('GET /', function(){
-    it('should default to text/html', function(done){
+describe('content-negotiation', () => {
+  describe('GET /', () => {
+    it('should default to text/html', (done) => {
       request(app)
-      .get('/')
-      .expect(200, '<ul><li>Tobi</li><li>Loki</li><li>Jane</li></ul>', done)
+        .get('/')
+        .expect(200, '<ul><li>Tobi</li><li>Loki</li><li>Jane</li></ul>', done)
     })
 
-    it('should accept to text/plain', function(done){
+    it('should accept to text/plain', (done) => {
       request(app)
-      .get('/')
-      .set('Accept', 'text/plain')
-      .expect(200, ' - Tobi\n - Loki\n - Jane\n', done)
+        .get('/')
+        .set('Accept', 'text/plain')
+        .expect(200, ' - Tobi\n - Loki\n - Jane\n', done)
     })
 
-    it('should accept to application/json', function(done){
+    it('should accept to application/json', (done) => {
       request(app)
-      .get('/')
-      .set('Accept', 'application/json')
-      .expect(200, '[{"name":"Tobi"},{"name":"Loki"},{"name":"Jane"}]', done)
+        .get('/')
+        .set('Accept', 'application/json')
+        .expect(200, '[{"name":"Tobi"},{"name":"Loki"},{"name":"Jane"}]', done)
     })
   })
 
-  describe('GET /users', function(){
-    it('should default to text/html', function(done){
+  describe('GET /users', () => {
+    it('should default to text/html', (done) => {
       request(app)
-      .get('/users')
-      .expect(200, '<ul><li>Tobi</li><li>Loki</li><li>Jane</li></ul>', done)
+        .get('/users')
+        .expect(200, '<ul><li>Tobi</li><li>Loki</li><li>Jane</li></ul>', done)
     })
 
-    it('should accept to text/plain', function(done){
+    it('should accept to text/plain', (done) => {
       request(app)
-      .get('/users')
-      .set('Accept', 'text/plain')
-      .expect(200, ' - Tobi\n - Loki\n - Jane\n', done)
+        .get('/users')
+        .set('Accept', 'text/plain')
+        .expect(200, ' - Tobi\n - Loki\n - Jane\n', done)
     })
 
-    it('should accept to application/json', function(done){
+    it('should accept to application/json', (done) => {
       request(app)
-      .get('/users')
-      .set('Accept', 'application/json')
-      .expect(200, '[{"name":"Tobi"},{"name":"Loki"},{"name":"Jane"}]', done)
+        .get('/users')
+        .set('Accept', 'application/json')
+        .expect(200, '[{"name":"Tobi"},{"name":"Loki"},{"name":"Jane"}]', done)
     })
   })
 })
diff --git a/test/acceptance/cookie-sessions.js b/test/acceptance/cookie-sessions.js
index e83c8e419da..59db5a50c41 100644
--- a/test/acceptance/cookie-sessions.js
+++ b/test/acceptance/cookie-sessions.js
@@ -1,38 +1,35 @@
+const app = require('../../examples/cookie-sessions/')
+const request = require('supertest')
 
-var app = require('../../examples/cookie-sessions')
-var request = require('supertest')
-
-describe('cookie-sessions', function () {
-  describe('GET /', function () {
-    it('should display no views', function (done) {
+describe('cookie-sessions', () => {
+  describe('GET /', () => {
+    it('should display no views', (done) => {
       request(app)
-      .get('/')
-      .expect(200, 'viewed 1 times\n', done)
+        .get('/')
+        .expect(200, 'viewed 1 times\n', done)
     })
 
-    it('should set a session cookie', function (done) {
+    it('should set a session cookie', (done) => {
       request(app)
-      .get('/')
-      .expect('Set-Cookie', /session=/)
-      .expect(200, done)
+        .get('/')
+        .expect('Set-Cookie', /session=/)
+        .expect(200, done)
     })
 
-    it('should display 1 view on revisit', function (done) {
+    it('should display 1 view on revisit', (done) => {
       request(app)
-      .get('/')
-      .expect(200, 'viewed 1 times\n', function (err, res) {
-        if (err) return done(err)
-        request(app)
         .get('/')
-        .set('Cookie', getCookies(res))
-        .expect(200, 'viewed 2 times\n', done)
-      })
+        .expect(200, 'viewed 1 times\n', (err, res) => {
+          if (err) return done(err)
+          request(app)
+            .get('/')
+            .set('Cookie', getCookies(res))
+            .expect(200, 'viewed 2 times\n', done)
+        })
     })
   })
 })
 
-function getCookies(res) {
-  return res.headers['set-cookie'].map(function (val) {
-    return val.split(';')[0]
-  }).join('; ');
+function getCookies (res) {
+  return res.headers['set-cookie'].map((val) => val.split(';')[0]).join('; ')
 }
diff --git a/test/acceptance/cookies.js b/test/acceptance/cookies.js
index aa9e1faef44..fec3b9276c5 100644
--- a/test/acceptance/cookies.js
+++ b/test/acceptance/cookies.js
@@ -1,71 +1,70 @@
+const app = require('../../examples/cookies/')
+const request = require('supertest')
+const utils = require('../support/utils')
 
-var app = require('../../examples/cookies')
-  , request = require('supertest');
-var utils = require('../support/utils');
-
-describe('cookies', function(){
-  describe('GET /', function(){
-    it('should have a form', function(done){
+describe('cookies', () => {
+  describe('GET /', () => {
+    it('should have a form', (done) => {
       request(app)
-      .get('/')
-      .expect(/<form/, done);
+        .get('/')
+        .expect(/<form/, done)
     })
 
-    it('should respond with no cookies', function(done){
+    it('should respond with no cookies', (done) => {
       request(app)
-      .get('/')
-      .expect(utils.shouldNotHaveHeader('Set-Cookie'))
-      .expect(200, done)
+        .get('/')
+        .expect(utils.shouldNotHaveHeader('Set-Cookie'))
+        .expect(200, done)
     })
 
-    it('should respond to cookie', function(done){
+    it('should respond to cookie', (done) => {
       request(app)
-      .post('/')
-      .type('urlencoded')
-      .send({ remember: 1 })
-      .expect(302, function(err, res){
-        if (err) return done(err)
-        request(app)
-        .get('/')
-        .set('Cookie', res.headers['set-cookie'][0])
-        .expect(200, /Remembered/, done)
-      })
+        .post('/')
+        .type('urlencoded')
+        .send({ remember: 1 })
+        .expect(302, (err, res) => {
+          if (err) return done(err)
+          request(app)
+            .get('/')
+            .set('Cookie', res.headers['set-cookie'][0])
+            .expect(200, /Remembered/, done)
+        })
     })
   })
 
-  describe('GET /forget', function(){
-    it('should clear cookie', function(done){
+  describe('GET /forget', () => {
+    it('should clear cookie', (done) => {
       request(app)
-      .post('/')
-      .type('urlencoded')
-      .send({ remember: 1 })
-      .expect(302, function(err, res){
-        if (err) return done(err)
-        request(app)
-        .get('/forget')
-        .set('Cookie', res.headers['set-cookie'][0])
-        .expect('Set-Cookie', /remember=;/)
-        .expect(302, done)
-      })
+        .post('/')
+        .type('urlencoded')
+        .send({ remember: 1 })
+        .expect(302, (err, res) => {
+          if (err) return done(err)
+          request(app)
+            .get('/forget')
+            .set('Cookie', res.headers['set-cookie'][0])
+            .expect('Set-Cookie', /remember=;/)
+            .expect(302, done)
+        })
     })
   })
 
-  describe('POST /', function(){
-    it('should set a cookie', function(done){
+  describe('POST /', () => {
+    it('should set a cookie', (done) => {
       request(app)
-      .post('/')
-      .type('urlencoded')
-      .send({ remember: 1 })
-      .expect('Set-Cookie', /remember=1/)
-      .expect(302, done)
+        .post('/')
+        .type('urlencoded')
+        .send({ remember: 1 })
+        .expect('Set-Cookie', /remember=1/)
+        .expect(302, done)
     })
 
-    it('should no set cookie w/o reminder', function(done){
+    it('should no set cookie w/o reminder', (done) => {
       request(app)
-      .post('/')
-      .send({})
-      .expect(utils.shouldNotHaveHeader('Set-Cookie'))
-      .expect(302, done)
+        .post('/')
+        .send({})
+        .expect(utils.shouldNotHaveHeader('Set-Cookie'))
+        .expect(302, done)
     })
   })
 })
diff --git a/test/acceptance/downloads.js b/test/acceptance/downloads.js
index 6db43b351e4..f2a55e97499 100644
--- a/test/acceptance/downloads.js
+++ b/test/acceptance/downloads.js
@@ -1,18 +1,17 @@
+const app = require('../../examples/downloads/')
+const request = require('supertest')
 
-var app = require('../../examples/downloads')
-  , request = require('supertest');
-
-describe('downloads', function(){
-  describe('GET /', function(){
-    it('should have a link to amazing.txt', function(done){
+describe('downloads', () => {
+  describe('GET /', () => {
+    it('should have a link to amazing.txt', (done) => {
       request(app)
-      .get('/')
-      .expect(/href="\/files\/amazing.txt"/, done)
+        .get('/')
+        .expect(/href="\/files\/amazing.txt"/, done)
     })
   })
 
-  describe('GET /files/notes/groceries.txt', function () {
-    it('should have a download header', function (done) {
+  describe('GET /files/notes/groceries.txt', () => {
+    it('should have a download header', (done) => {
       request(app)
         .get('/files/notes/groceries.txt')
         .expect('Content-Disposition', 'attachment; filename="groceries.txt"')
@@ -20,25 +19,25 @@ describe('downloads', function(){
     })
   })
 
-  describe('GET /files/amazing.txt', function(){
-    it('should have a download header', function(done){
+  describe('GET /files/amazing.txt', () => {
+    it('should have a download header', (done) => {
       request(app)
-      .get('/files/amazing.txt')
-      .expect('Content-Disposition', 'attachment; filename="amazing.txt"')
-      .expect(200, done)
+        .get('/files/amazing.txt')
+        .expect('Content-Disposition', 'attachment; filename="amazing.txt"')
+        .expect(200, done)
     })
   })
 
-  describe('GET /files/missing.txt', function(){
-    it('should respond with 404', function(done){
+  describe('GET /files/missing.txt', () => {
+    it('should respond with 404', (done) => {
       request(app)
-      .get('/files/missing.txt')
-      .expect(404, done)
+        .get('/files/missing.txt')
+        .expect(404, done)
     })
   })
 
-  describe('GET /files/../index.js', function () {
-    it('should respond with 403', function (done) {
+  describe('GET /files/../index.js', () => {
+    it('should respond with 403', (done) => {
       request(app)
         .get('/files/../index.js')
         .expect(403, done)
diff --git a/test/acceptance/ejs.js b/test/acceptance/ejs.js
index 12defcb564f..df3a1c27704 100644
--- a/test/acceptance/ejs.js
+++ b/test/acceptance/ejs.js
@@ -1,17 +1,16 @@
+const request = require('supertest')
+const app = require('../../examples/ejs/')
 
-var request = require('supertest')
-  , app = require('../../examples/ejs');
-
-describe('ejs', function(){
-  describe('GET /', function(){
-    it('should respond with html', function(done){
+describe('ejs', () => {
+  describe('GET /', () => {
+    it('should respond with html', (done) => {
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/html; charset=utf-8')
-      .expect(/<li>tobi &lt;tobi@learnboost\.com&gt;<\/li>/)
-      .expect(/<li>loki &lt;loki@learnboost\.com&gt;<\/li>/)
-      .expect(/<li>jane &lt;jane@learnboost\.com&gt;<\/li>/)
-      .expect(200, done)
+        .get('/')
+        .expect('Content-Type', 'text/html; charset=utf-8')
+        .expect(/<li>tobi &lt;tobi@learnboost\.com&gt;<\/li>/)
+        .expect(/<li>loki &lt;loki@learnboost\.com&gt;<\/li>/)
+        .expect(/<li>jane &lt;jane@learnboost\.com&gt;<\/li>/)
+        .expect(200, done)
     })
   })
 })
diff --git a/test/acceptance/error-pages.js b/test/acceptance/error-pages.js
index 48feb3fb466..1fddbd3cfed 100644
--- a/test/acceptance/error-pages.js
+++ b/test/acceptance/error-pages.js
@@ -1,98 +1,96 @@
+const app = require('../../examples/error-pages/')
+const request = require('supertest')
 
-var app = require('../../examples/error-pages')
-  , request = require('supertest');
-
-describe('error-pages', function(){
-  describe('GET /', function(){
-    it('should respond with page list', function(done){
+describe('error-pages', () => {
+  describe('GET /', () => {
+    it('should respond with page list', (done) => {
       request(app)
-      .get('/')
-      .expect(/Pages Example/, done)
+        .get('/')
+        .expect(/Pages Example/, done)
     })
   })
 
-  describe('Accept: text/html',function(){
-    describe('GET /403', function(){
-      it('should respond with 403', function(done){
+  describe('Accept: text/html', () => {
+    describe('GET /403', () => {
+      it('should respond with 403', (done) => {
         request(app)
-        .get('/403')
-        .expect(403, done)
+          .get('/403')
+          .expect(403, done)
       })
     })
 
-    describe('GET /404', function(){
-      it('should respond with 404', function(done){
+    describe('GET /404', () => {
+      it('should respond with 404', (done) => {
         request(app)
-        .get('/404')
-        .expect(404, done)
+          .get('/404')
+          .expect(404, done)
       })
     })
 
-    describe('GET /500', function(){
-      it('should respond with 500', function(done){
+    describe('GET /500', () => {
+      it('should respond with 500', (done) => {
         request(app)
-        .get('/500')
-        .expect(500, done)
+          .get('/500')
+          .expect(500, done)
       })
     })
   })
 
-  describe('Accept: application/json',function(){
-    describe('GET /403', function(){
-      it('should respond with 403', function(done){
+  describe('Accept: application/json', () => {
+    describe('GET /403', () => {
+      it('should respond with 403', (done) => {
         request(app)
-        .get('/403')
-        .set('Accept','application/json')
-        .expect(403, done)
+          .get('/403')
+          .set('Accept', 'application/json')
+          .expect(403, done)
       })
     })
 
-    describe('GET /404', function(){
-      it('should respond with 404', function(done){
+    describe('GET /404', () => {
+      it('should respond with 404', (done) => {
         request(app)
-        .get('/404')
-        .set('Accept','application/json')
-        .expect(404, { error: 'Not found' }, done)
+          .get('/404')
+          .set('Accept', 'application/json')
+          .expect(404, { error: 'Not found' }, done)
       })
     })
 
-    describe('GET /500', function(){
-      it('should respond with 500', function(done){
+    describe('GET /500', () => {
+      it('should respond with 500', (done) => {
         request(app)
-        .get('/500')
-        .set('Accept', 'application/json')
-        .expect(500, done)
+          .get('/500')
+          .set('Accept', 'application/json')
+          .expect(500, done)
       })
     })
   })
 
-
-  describe('Accept: text/plain',function(){
-    describe('GET /403', function(){
-      it('should respond with 403', function(done){
+  describe('Accept: text/plain', () => {
+    describe('GET /403', () => {
+      it('should respond with 403', (done) => {
         request(app)
-        .get('/403')
-        .set('Accept','text/plain')
-        .expect(403, done)
+          .get('/403')
+          .set('Accept', 'text/plain')
+          .expect(403, done)
       })
     })
 
-    describe('GET /404', function(){
-      it('should respond with 404', function(done){
+    describe('GET /404', () => {
+      it('should respond with 404', (done) => {
         request(app)
-        .get('/404')
-        .set('Accept', 'text/plain')
-        .expect(404)
-        .expect('Not found', done);
+          .get('/404')
+          .set('Accept', 'text/plain')
+          .expect(404)
+          .expect('Not found', done)
       })
     })
 
-    describe('GET /500', function(){
-      it('should respond with 500', function(done){
+    describe('GET /500', () => {
+      it('should respond with 500', (done) => {
         request(app)
-        .get('/500')
-        .set('Accept','text/plain')
-        .expect(500, done)
+          .get('/500')
+          .set('Accept', 'text/plain')
+          .expect(500, done)
       })
     })
   })
diff --git a/test/acceptance/error.js b/test/acceptance/error.js
index 6bdf099feed..c28b4724bea 100644
--- a/test/acceptance/error.js
+++ b/test/acceptance/error.js
@@ -1,29 +1,28 @@
+const app = require('../../examples/error/')
+const request = require('supertest')
 
-var app = require('../../examples/error')
-  , request = require('supertest');
-
-describe('error', function(){
-  describe('GET /', function(){
-    it('should respond with 500', function(done){
+describe('error', () => {
+  describe('GET /', () => {
+    it('should respond with 500', (done) => {
       request(app)
         .get('/')
-        .expect(500,done)
+        .expect(500, done)
     })
   })
 
-  describe('GET /next', function(){
-    it('should respond with 500', function(done){
+  describe('GET /next', () => {
+    it('should respond with 500', (done) => {
       request(app)
         .get('/next')
-        .expect(500,done)
+        .expect(500, done)
     })
   })
 
-  describe('GET /missing', function(){
-    it('should respond with 404', function(done){
+  describe('GET /missing', () => {
+    it('should respond with 404', (done) => {
       request(app)
         .get('/missing')
-        .expect(404,done)
+        .expect(404, done)
     })
   })
 })
diff --git a/test/acceptance/hello-world.js b/test/acceptance/hello-world.js
index db90349c496..797cfd739bc 100644
--- a/test/acceptance/hello-world.js
+++ b/test/acceptance/hello-world.js
@@ -1,18 +1,17 @@
+const app = require('../../examples/hello-world/')
+const request = require('supertest')
 
-var app = require('../../examples/hello-world')
-var request = require('supertest')
-
-describe('hello-world', function () {
-  describe('GET /', function () {
-    it('should respond with hello world', function (done) {
+describe('hello-world', () => {
+  describe('GET /', () => {
+    it('should respond with hello world', (done) => {
       request(app)
         .get('/')
         .expect(200, 'Hello World', done)
     })
   })
 
-  describe('GET /missing', function () {
-    it('should respond with 404', function (done) {
+  describe('GET /missing', () => {
+    it('should respond with 404', (done) => {
       request(app)
         .get('/missing')
         .expect(404, done)
diff --git a/test/acceptance/markdown.js b/test/acceptance/markdown.js
index 1a7d9e3cb75..34e31fb41f3 100644
--- a/test/acceptance/markdown.js
+++ b/test/acceptance/markdown.js
@@ -1,21 +1,20 @@
+const app = require('../../examples/markdown/')
+const request = require('supertest')
 
-var app = require('../../examples/markdown')
-var request = require('supertest')
-
-describe('markdown', function(){
-  describe('GET /', function(){
-    it('should respond with html', function(done){
+describe('markdown', () => {
+  describe('GET /', () => {
+    it('should respond with html', (done) => {
       request(app)
         .get('/')
-        .expect(/<h1[^>]*>Markdown Example<\/h1>/,done)
+        .expect(/<h1[^>]*>Markdown Example<\/h1>/, done)
     })
   })
 
-  describe('GET /fail',function(){
-    it('should respond with an error', function(done){
+  describe('GET /fail', () => {
+    it('should respond with an error', (done) => {
       request(app)
         .get('/fail')
-        .expect(500,done)
+        .expect(500, done)
     })
   })
 })
diff --git a/test/acceptance/multi-router.js b/test/acceptance/multi-router.js
index 4362a8300be..afb5fe6a52a 100644
--- a/test/acceptance/multi-router.js
+++ b/test/acceptance/multi-router.js
@@ -1,44 +1,44 @@
-var app = require('../../examples/multi-router')
-var request = require('supertest')
+const app = require('../../examples/multi-router/')
+const request = require('supertest')
 
-describe('multi-router', function(){
-  describe('GET /',function(){
-    it('should respond with root handler', function(done){
+describe('multi-router', () => {
+  describe('GET /', () => {
+    it('should respond with root handler', (done) => {
       request(app)
-      .get('/')
-      .expect(200, 'Hello from root route.', done)
+        .get('/')
+        .expect(200, 'Hello from root route.', done)
     })
   })
 
-  describe('GET /api/v1/',function(){
-    it('should respond with APIv1 root handler', function(done){
+  describe('GET /api/v1/', () => {
+    it('should respond with APIv1 root handler', (done) => {
       request(app)
-      .get('/api/v1/')
-      .expect(200, 'Hello from APIv1 root route.', done)
+        .get('/api/v1/')
+        .expect(200, 'Hello from APIv1 root route.', done)
     })
   })
 
-  describe('GET /api/v1/users',function(){
-    it('should respond with users from APIv1', function(done){
+  describe('GET /api/v1/users', () => {
+    it('should respond with users from APIv1', (done) => {
       request(app)
-      .get('/api/v1/users')
-      .expect(200, 'List of APIv1 users.', done)
+        .get('/api/v1/users')
+        .expect(200, 'List of APIv1 users.', done)
     })
   })
 
-  describe('GET /api/v2/',function(){
-    it('should respond with APIv2 root handler', function(done){
+  describe('GET /api/v2/', () => {
+    it('should respond with APIv2 root handler', (done) => {
       request(app)
-      .get('/api/v2/')
-      .expect(200, 'Hello from APIv2 root route.', done)
+        .get('/api/v2/')
+        .expect(200, 'Hello from APIv2 root route.', done)
     })
   })
 
-  describe('GET /api/v2/users',function(){
-    it('should respond with users from APIv2', function(done){
+  describe('GET /api/v2/users', () => {
+    it('should respond with users from APIv2', (done) => {
       request(app)
-      .get('/api/v2/users')
-      .expect(200, 'List of APIv2 users.', done)
+        .get('/api/v2/users')
+        .expect(200, 'List of APIv2 users.', done)
     })
   })
 })
diff --git a/test/acceptance/mvc.js b/test/acceptance/mvc.js
index 35709f6fb46..8a777a664ac 100644
--- a/test/acceptance/mvc.js
+++ b/test/acceptance/mvc.js
@@ -1,132 +1,131 @@
+const request = require('supertest')
+const app = require('../../examples/mvc/')
 
-var request = require('supertest')
-  , app = require('../../examples/mvc');
-
-describe('mvc', function(){
-  describe('GET /', function(){
-    it('should redirect to /users', function(done){
+describe('mvc', () => {
+  describe('GET /', () => {
+    it('should redirect to /users', (done) => {
       request(app)
-      .get('/')
-      .expect('Location', '/users')
-      .expect(302, done)
+        .get('/')
+        .expect('Location', '/users')
+        .expect(302, done)
     })
   })
 
-  describe('GET /pet/0', function(){
-    it('should get pet', function(done){
+  describe('GET /pet/0', () => {
+    it('should get pet', (done) => {
       request(app)
-      .get('/pet/0')
-      .expect(200, /Tobi/, done)
+        .get('/pet/0')
+        .expect(200, /Tobi/, done)
     })
   })
 
-  describe('GET /pet/0/edit', function(){
-    it('should get pet edit page', function(done){
+  describe('GET /pet/0/edit', () => {
+    it('should get pet edit page', (done) => {
       request(app)
-      .get('/pet/0/edit')
-      .expect(/<form/)
-      .expect(200, /Tobi/, done)
+        .get('/pet/0/edit')
+        .expect(/<form/)
+        .expect(200, /Tobi/, done)
     })
   })
 
-  describe('PUT /pet/2', function(){
-    it('should update the pet', function(done){
+  describe('PUT /pet/2', () => {
+    it('should update the pet', (done) => {
       request(app)
-      .put('/pet/3')
-      .set('Content-Type', 'application/x-www-form-urlencoded')
-      .send({ pet: { name: 'Boots' } })
-      .expect(302, function (err, res) {
-        if (err) return done(err);
-        request(app)
-        .get('/pet/3/edit')
-        .expect(200, /Boots/, done)
-      })
+        .put('/pet/3')
+        .set('Content-Type', 'application/x-www-form-urlencoded')
+        .send({ pet: { name: 'Boots' } })
+        .expect(302, (err, res) => {
+          if (err) return done(err)
+          request(app)
+            .get('/pet/3/edit')
+            .expect(200, /Boots/, done)
+        })
     })
   })
 
-  describe('GET /users', function(){
-    it('should display a list of users', function(done){
+  describe('GET /users', () => {
+    it('should display a list of users', (done) => {
       request(app)
-      .get('/users')
-      .expect(/<h1>Users<\/h1>/)
-      .expect(/>TJ</)
-      .expect(/>Guillermo</)
-      .expect(/>Nathan</)
-      .expect(200, done)
+        .get('/users')
+        .expect(/<h1>Users<\/h1>/)
+        .expect(/>TJ</)
+        .expect(/>Guillermo</)
+        .expect(/>Nathan</)
+        .expect(200, done)
     })
   })
 
-  describe('GET /user/:id', function(){
-    describe('when present', function(){
-      it('should display the user', function(done){
+  describe('GET /user/:id', () => {
+    describe('when present', () => {
+      it('should display the user', (done) => {
         request(app)
-        .get('/user/0')
-        .expect(200, /<h1>TJ <a href="\/user\/0\/edit">edit/, done)
+          .get('/user/0')
+          .expect(200, /<h1>TJ <a href="\/user\/0\/edit">edit/, done)
       })
 
-      it('should display the users pets', function(done){
+      it('should display the users pets', (done) => {
         request(app)
-        .get('/user/0')
-        .expect(/\/pet\/0">Tobi/)
-        .expect(/\/pet\/1">Loki/)
-        .expect(/\/pet\/2">Jane/)
-        .expect(200, done)
+          .get('/user/0')
+          .expect(/\/pet\/0">Tobi/)
+          .expect(/\/pet\/1">Loki/)
+          .expect(/\/pet\/2">Jane/)
+          .expect(200, done)
       })
     })
 
-    describe('when not present', function(){
-      it('should 404', function(done){
+    describe('when not present', () => {
+      it('should 404', (done) => {
         request(app)
-        .get('/user/123')
-        .expect(404, done);
+          .get('/user/123')
+          .expect(404, done)
       })
     })
   })
 
-  describe('GET /user/:id/edit', function(){
-    it('should display the edit form', function(done){
+  describe('GET /user/:id/edit', () => {
+    it('should display the edit form', (done) => {
       request(app)
-      .get('/user/1/edit')
-      .expect(/Guillermo/)
-      .expect(200, /<form/, done)
+        .get('/user/1/edit')
+        .expect(/Guillermo/)
+        .expect(200, /<form/, done)
     })
   })
 
-  describe('PUT /user/:id', function(){
-    it('should 500 on error', function(done){
+  describe('PUT /user/:id', () => {
+    it('should 500 on error', (done) => {
       request(app)
-      .put('/user/1')
-      .send({})
-      .expect(500, done)
+        .put('/user/1')
+        .send({})
+        .expect(500, done)
     })
 
-    it('should update the user', function(done){
+    it('should update the user', (done) => {
       request(app)
-      .put('/user/1')
-      .set('Content-Type', 'application/x-www-form-urlencoded')
-      .send({ user: { name: 'Tobo' }})
-      .expect(302, function (err, res) {
-        if (err) return done(err);
-        request(app)
-        .get('/user/1/edit')
-        .expect(200, /Tobo/, done)
-      })
+        .put('/user/1')
+        .set('Content-Type', 'application/x-www-form-urlencoded')
+        .send({ user: { name: 'Tobo' } })
+        .expect(302, (err, res) => {
+          if (err) return done(err)
+          request(app)
+            .get('/user/1/edit')
+            .expect(200, /Tobo/, done)
+        })
     })
   })
 
-  describe('POST /user/:id/pet', function(){
-    it('should create a pet for user', function(done){
+  describe('POST /user/:id/pet', () => {
+    it('should create a pet for user', (done) => {
       request(app)
-      .post('/user/2/pet')
-      .set('Content-Type', 'application/x-www-form-urlencoded')
-      .send({ pet: { name: 'Snickers' }})
-      .expect('Location', '/user/2')
-      .expect(302, function(err, res){
-        if (err) return done(err)
-        request(app)
-        .get('/user/2')
-        .expect(200, /Snickers/, done)
-      })
+        .post('/user/2/pet')
+        .set('Content-Type', 'application/x-www-form-urlencoded')
+        .send({ pet: { name: 'Snickers' } })
+        .expect('Location', '/user/2')
+        .expect(302, (err, res) => {
+          if (err) return done(err)
+          request(app)
+            .get('/user/2')
+            .expect(200, /Snickers/, done)
+        })
     })
   })
 })
diff --git a/test/acceptance/params.js b/test/acceptance/params.js
index e7c30cf7732..c98bd6afe5f 100644
--- a/test/acceptance/params.js
+++ b/test/acceptance/params.js
@@ -1,44 +1,44 @@
-var app = require('../../examples/params')
-var request = require('supertest')
+const app = require('../../examples/params/')
+const request = require('supertest')
 
-describe('params', function(){
-  describe('GET /', function(){
-    it('should respond with instructions', function(done){
+describe('params', () => {
+  describe('GET /', () => {
+    it('should respond with instructions', (done) => {
       request(app)
         .get('/')
-        .expect(/Visit/,done)
+        .expect(/Visit/, done)
     })
   })
 
-  describe('GET /user/0', function(){
-    it('should respond with a user', function(done){
+  describe('GET /user/0', () => {
+    it('should respond with a user', (done) => {
       request(app)
         .get('/user/0')
-        .expect(/user tj/,done)
+        .expect(/user tj/, done)
     })
   })
 
-  describe('GET /user/9', function(){
-    it('should fail to find user', function(done){
+  describe('GET /user/9', () => {
+    it('should fail to find user', (done) => {
       request(app)
-      .get('/user/9')
-      .expect(404, /failed to find user/, done)
+        .get('/user/9')
+        .expect(404, /failed to find user/, done)
     })
   })
 
-  describe('GET /users/0-2', function(){
-    it('should respond with three users', function(done){
+  describe('GET /users/0-2', () => {
+    it('should respond with three users', (done) => {
       request(app)
-      .get('/users/0-2')
-      .expect(/users tj, tobi, loki/, done)
+        .get('/users/0-2')
+        .expect(/users tj, tobi, loki/, done)
     })
   })
 
-  describe('GET /users/foo-bar', function(){
-    it('should fail integer parsing', function(done){
+  describe('GET /users/foo-bar', () => {
+    it('should fail integer parsing', (done) => {
       request(app)
-      .get('/users/foo-bar')
-      .expect(400, /failed to parseInt foo/, done)
+        .get('/users/foo-bar')
+        .expect(400, /failed to parseInt foo/, done)
     })
   })
 })
diff --git a/test/acceptance/resource.js b/test/acceptance/resource.js
index a2db7bd3fd2..ecc69b6d30e 100644
--- a/test/acceptance/resource.js
+++ b/test/acceptance/resource.js
@@ -1,68 +1,68 @@
-var app = require('../../examples/resource')
-var request = require('supertest')
+const app = require('../../examples/resource/')
+const request = require('supertest')
 
-describe('resource', function(){
-  describe('GET /', function(){
-    it('should respond with instructions', function(done){
+describe('resource', () => {
+  describe('GET /', () => {
+    it('should respond with instructions', (done) => {
       request(app)
         .get('/')
-        .expect(/^<h1>Examples:<\/h1>/,done)
+        .expect(/^<h1>Examples:<\/h1>/, done)
     })
   })
 
-  describe('GET /users', function(){
-    it('should respond with all users', function(done){
+  describe('GET /users', () => {
+    it('should respond with all users', (done) => {
       request(app)
         .get('/users')
-        .expect(/^\[{"name":"tj"},{"name":"ciaran"},{"name":"aaron"},{"name":"guillermo"},{"name":"simon"},{"name":"tobi"}\]/,done)
+        .expect(/^\[{"name":"tj"},{"name":"ciaran"},{"name":"aaron"},{"name":"guillermo"},{"name":"simon"},{"name":"tobi"}\]/, done)
     })
   })
 
-  describe('GET /users/1', function(){
-    it('should respond with user 1', function(done){
+  describe('GET /users/1', () => {
+    it('should respond with user 1', (done) => {
       request(app)
         .get('/users/1')
-        .expect(/^{"name":"ciaran"}/,done)
+        .expect(/^{"name":"ciaran"}/, done)
     })
   })
 
-  describe('GET /users/9', function(){
-    it('should respond with error', function(done){
+  describe('GET /users/9', () => {
+    it('should respond with error', (done) => {
       request(app)
         .get('/users/9')
         .expect('{"error":"Cannot find user"}', done)
     })
   })
 
-  describe('GET /users/1..3', function(){
-    it('should respond with users 1 through 3', function(done){
+  describe('GET /users/1..3', () => {
+    it('should respond with users 1 through 3', (done) => {
       request(app)
         .get('/users/1..3')
-        .expect(/^<ul><li>ciaran<\/li>\n<li>aaron<\/li>\n<li>guillermo<\/li><\/ul>/,done)
+        .expect(/^<ul><li>ciaran<\/li>\n<li>aaron<\/li>\n<li>guillermo<\/li><\/ul>/, done)
     })
   })
 
-  describe('DELETE /users/1', function(){
-    it('should delete user 1', function(done){
+  describe('DELETE /users/1', () => {
+    it('should delete user 1', (done) => {
       request(app)
         .del('/users/1')
-        .expect(/^destroyed/,done)
+        .expect(/^destroyed/, done)
     })
   })
 
-  describe('DELETE /users/9', function(){
-    it('should fail', function(done){
+  describe('DELETE /users/9', () => {
+    it('should fail', (done) => {
       request(app)
         .del('/users/9')
         .expect('Cannot find user', done)
     })
   })
 
-  describe('GET /users/1..3.json', function(){
-    it('should respond with users 2 and 3 as json', function(done){
+  describe('GET /users/1..3.json', () => {
+    it('should respond with users 2 and 3 as json', (done) => {
       request(app)
         .get('/users/1..3.json')
-        .expect(/^\[null,{"name":"aaron"},{"name":"guillermo"}\]/,done)
+        .expect(/^\[null,{"name":"aaron"},{"name":"guillermo"}\]/, done)
     })
   })
 })
diff --git a/test/acceptance/route-map.js b/test/acceptance/route-map.js
index 0bd2a6d32e1..7b79fe3c33b 100644
--- a/test/acceptance/route-map.js
+++ b/test/acceptance/route-map.js
@@ -1,45 +1,44 @@
+const request = require('supertest')
+const app = require('../../examples/route-map/')
 
-var request = require('supertest')
-  , app = require('../../examples/route-map');
-
-describe('route-map', function(){
-  describe('GET /users', function(){
-    it('should respond with users', function(done){
+describe('route-map', () => {
+  describe('GET /users', () => {
+    it('should respond with users', (done) => {
       request(app)
-      .get('/users')
-      .expect('user list', done);
+        .get('/users')
+        .expect('user list', done)
     })
   })
 
-  describe('DELETE /users', function(){
-    it('should delete users', function(done){
+  describe('DELETE /users', () => {
+    it('should delete users', (done) => {
       request(app)
-      .del('/users')
-      .expect('delete users', done);
+        .del('/users')
+        .expect('delete users', done)
     })
   })
 
-  describe('GET /users/:id', function(){
-    it('should get a user', function(done){
+  describe('GET /users/:id', () => {
+    it('should get a user', (done) => {
       request(app)
-      .get('/users/12')
-      .expect('user 12', done);
+        .get('/users/12')
+        .expect('user 12', done)
     })
   })
 
-  describe('GET /users/:id/pets', function(){
-    it('should get a users pets', function(done){
+  describe('GET /users/:id/pets', () => {
+    it('should get a users pets', (done) => {
       request(app)
-      .get('/users/12/pets')
-      .expect('user 12\'s pets', done);
+        .get('/users/12/pets')
+        .expect('user 12\'s pets', done)
     })
   })
 
-  describe('GET /users/:id/pets/:pid', function(){
-    it('should get a users pet', function(done){
+  describe('GET /users/:id/pets/:pid', () => {
+    it('should get a users pet', (done) => {
       request(app)
-      .del('/users/12/pets/2')
-      .expect('delete 12\'s pet 2', done);
+        .del('/users/12/pets/2')
+        .expect('delete 12\'s pet 2', done)
     })
   })
 })
diff --git a/test/acceptance/route-separation.js b/test/acceptance/route-separation.js
index 867fd295271..bf2b72fc25b 100644
--- a/test/acceptance/route-separation.js
+++ b/test/acceptance/route-separation.js
@@ -1,97 +1,96 @@
+const app = require('../../examples/route-separation/')
+const request = require('supertest')
 
-var app = require('../../examples/route-separation')
-var request = require('supertest')
-
-describe('route-separation', function () {
-  describe('GET /', function () {
-    it('should respond with index', function (done) {
+describe('route-separation', () => {
+  describe('GET /', () => {
+    it('should respond with index', (done) => {
       request(app)
-      .get('/')
-      .expect(200, /Route Separation Example/, done)
+        .get('/')
+        .expect(200, /Route Separation Example/, done)
     })
   })
 
-  describe('GET /users', function () {
-    it('should list users', function (done) {
+  describe('GET /users', () => {
+    it('should list users', (done) => {
       request(app)
-      .get('/users')
-      .expect(/TJ/)
-      .expect(/Tobi/)
-      .expect(200, done)
+        .get('/users')
+        .expect(/TJ/)
+        .expect(/Tobi/)
+        .expect(200, done)
     })
   })
 
-  describe('GET /user/:id', function () {
-    it('should get a user', function (done) {
+  describe('GET /user/:id', () => {
+    it('should get a user', (done) => {
       request(app)
-      .get('/user/0')
-      .expect(200, /Viewing user TJ/, done)
+        .get('/user/0')
+        .expect(200, /Viewing user TJ/, done)
     })
 
-    it('should 404 on missing user', function (done) {
+    it('should 404 on missing user', (done) => {
       request(app)
-      .get('/user/10')
-      .expect(404, done)
+        .get('/user/10')
+        .expect(404, done)
     })
   })
 
-  describe('GET /user/:id/view', function () {
-    it('should get a user', function (done) {
+  describe('GET /user/:id/view', () => {
+    it('should get a user', (done) => {
       request(app)
-      .get('/user/0/view')
-      .expect(200, /Viewing user TJ/, done)
+        .get('/user/0/view')
+        .expect(200, /Viewing user TJ/, done)
     })
 
-    it('should 404 on missing user', function (done) {
+    it('should 404 on missing user', (done) => {
       request(app)
-      .get('/user/10/view')
-      .expect(404, done)
+        .get('/user/10/view')
+        .expect(404, done)
     })
   })
 
-  describe('GET /user/:id/edit', function () {
-    it('should get a user to edit', function (done) {
+  describe('GET /user/:id/edit', () => {
+    it('should get a user to edit', (done) => {
       request(app)
-      .get('/user/0/edit')
-      .expect(200, /Editing user TJ/, done)
+        .get('/user/0/edit')
+        .expect(200, /Editing user TJ/, done)
     })
   })
 
-  describe('PUT /user/:id/edit', function () {
-    it('should edit a user', function (done) {
+  describe('PUT /user/:id/edit', () => {
+    it('should edit a user', (done) => {
       request(app)
-      .put('/user/0/edit')
-      .set('Content-Type', 'application/x-www-form-urlencoded')
-      .send({ user: { name: 'TJ', email: 'tj-invalid@vision-media.ca' } })
-      .expect(302, function (err) {
-        if (err) return done(err)
-        request(app)
-        .get('/user/0')
-        .expect(200, /tj-invalid@vision-media\.ca/, done)
-      })
+        .put('/user/0/edit')
+        .set('Content-Type', 'application/x-www-form-urlencoded')
+        .send({ user: { name: 'TJ', email: 'tj-invalid@vision-media.ca' } })
+        .expect(302, (err) => {
+          if (err) return done(err)
+          request(app)
+            .get('/user/0')
+            .expect(200, /tj-invalid@vision-media\.ca/, done)
+        })
     })
   })
 
-  describe('POST /user/:id/edit?_method=PUT', function () {
-    it('should edit a user', function (done) {
+  describe('POST /user/:id/edit?_method=PUT', () => {
+    it('should edit a user', (done) => {
       request(app)
-      .post('/user/1/edit?_method=PUT')
-      .set('Content-Type', 'application/x-www-form-urlencoded')
-      .send({ user: { name: 'Tobi', email: 'tobi-invalid@vision-media.ca' } })
-      .expect(302, function (err) {
-        if (err) return done(err)
-        request(app)
-        .get('/user/1')
-        .expect(200, /tobi-invalid@vision-media\.ca/, done)
-      })
+        .post('/user/1/edit?_method=PUT')
+        .set('Content-Type', 'application/x-www-form-urlencoded')
+        .send({ user: { name: 'Tobi', email: 'tobi-invalid@vision-media.ca' } })
+        .expect(302, (err) => {
+          if (err) return done(err)
+          request(app)
+            .get('/user/1')
+            .expect(200, /tobi-invalid@vision-media\.ca/, done)
+        })
     })
   })
 
-  describe('GET /posts', function () {
-    it('should get a list of posts', function (done) {
+  describe('GET /posts', () => {
+    it('should get a list of posts', (done) => {
       request(app)
-      .get('/posts')
-      .expect(200, /Posts/, done)
+        .get('/posts')
+        .expect(200, /Posts/, done)
     })
   })
 })
diff --git a/test/acceptance/vhost.js b/test/acceptance/vhost.js
index 1b633d4b2bc..a7cac6b12f7 100644
--- a/test/acceptance/vhost.js
+++ b/test/acceptance/vhost.js
@@ -1,45 +1,45 @@
-var app = require('../../examples/vhost')
-var request = require('supertest')
+const app = require('../../examples/vhost/')
+const request = require('supertest')
 
-describe('vhost', function(){
-  describe('example.com', function(){
-    describe('GET /', function(){
-      it('should say hello', function(done){
+describe('vhost', () => {
+  describe('example.com', () => {
+    describe('GET /', () => {
+      it('should say hello', (done) => {
         request(app)
-        .get('/')
-        .set('Host', 'example.com')
-        .expect(200, /hello/i, done)
+          .get('/')
+          .set('Host', 'example.com')
+          .expect(200, /hello/i, done)
       })
     })
 
-    describe('GET /foo', function(){
-      it('should say foo', function(done){
+    describe('GET /foo', () => {
+      it('should say foo', (done) => {
         request(app)
-        .get('/foo')
-        .set('Host', 'example.com')
-        .expect(200, 'requested foo', done)
+          .get('/foo')
+          .set('Host', 'example.com')
+          .expect(200, 'requested foo', done)
       })
     })
   })
 
-  describe('foo.example.com', function(){
-    describe('GET /', function(){
-      it('should redirect to /foo', function(done){
+  describe('foo.example.com', () => {
+    describe('GET /', () => {
+      it('should redirect to /foo', (done) => {
         request(app)
-        .get('/')
-        .set('Host', 'foo.example.com')
-        .expect(302, /Redirecting to http:\/\/example.com:3000\/foo/, done)
+          .get('/')
+          .set('Host', 'foo.example.com')
+          .expect(302, /Redirecting to http:\/\/example.com:3000\/foo/, done)
       })
     })
   })
 
-  describe('bar.example.com', function(){
-    describe('GET /', function(){
-      it('should redirect to /bar', function(done){
+  describe('bar.example.com', () => {
+    describe('GET /', () => {
+      it('should redirect to /bar', (done) => {
         request(app)
-        .get('/')
-        .set('Host', 'bar.example.com')
-        .expect(302, /Redirecting to http:\/\/example.com:3000\/bar/, done)
+          .get('/')
+          .set('Host', 'bar.example.com')
+          .expect(302, /Redirecting to http:\/\/example.com:3000\/bar/, done)
       })
     })
   })
diff --git a/test/acceptance/web-service.js b/test/acceptance/web-service.js
index 2e37b48c8ca..06c0e040f92 100644
--- a/test/acceptance/web-service.js
+++ b/test/acceptance/web-service.js
@@ -1,101 +1,100 @@
+const request = require('supertest')
+const app = require('../../examples/web-service/')
 
-var request = require('supertest')
-  , app = require('../../examples/web-service');
-
-describe('web-service', function(){
-  describe('GET /api/users', function(){
-    describe('without an api key', function(){
-      it('should respond with 400 bad request', function(done){
+describe('web-service', () => {
+  describe('GET /api/users', () => {
+    describe('without an api key', () => {
+      it('should respond with 400 bad request', (done) => {
         request(app)
-        .get('/api/users')
-        .expect(400, done);
+          .get('/api/users')
+          .expect(400, done)
       })
     })
 
-    describe('with an invalid api key', function(){
-      it('should respond with 401 unauthorized', function(done){
+    describe('with an invalid api key', () => {
+      it('should respond with 401 unauthorized', (done) => {
         request(app)
-        .get('/api/users?api-key=rawr')
-        .expect(401, done);
+          .get('/api/users?api-key=rawr')
+          .expect(401, done)
       })
     })
 
-    describe('with a valid api key', function(){
-      it('should respond users json', function(done){
+    describe('with a valid api key', () => {
+      it('should respond users json', (done) => {
         request(app)
-        .get('/api/users?api-key=foo')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '[{"name":"tobi"},{"name":"loki"},{"name":"jane"}]', done)
+          .get('/api/users?api-key=foo')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '[{"name":"tobi"},{"name":"loki"},{"name":"jane"}]', done)
       })
     })
   })
 
-  describe('GET /api/repos', function(){
-    describe('without an api key', function(){
-      it('should respond with 400 bad request', function(done){
+  describe('GET /api/repos', () => {
+    describe('without an api key', () => {
+      it('should respond with 400 bad request', (done) => {
         request(app)
-        .get('/api/repos')
-        .expect(400, done);
+          .get('/api/repos')
+          .expect(400, done)
       })
     })
 
-    describe('with an invalid api key', function(){
-      it('should respond with 401 unauthorized', function(done){
+    describe('with an invalid api key', () => {
+      it('should respond with 401 unauthorized', (done) => {
         request(app)
-        .get('/api/repos?api-key=rawr')
-        .expect(401, done);
+          .get('/api/repos?api-key=rawr')
+          .expect(401, done)
       })
     })
 
-    describe('with a valid api key', function(){
-      it('should respond repos json', function(done){
+    describe('with a valid api key', () => {
+      it('should respond repos json', (done) => {
         request(app)
-        .get('/api/repos?api-key=foo')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(/"name":"express"/)
-        .expect(/"url":"https:\/\/github.com\/expressjs\/express"/)
-        .expect(200, done)
+          .get('/api/repos?api-key=foo')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(/"name":"express"/)
+          .expect(/"url":"https:\/\/github.com\/expressjs\/express"/)
+          .expect(200, done)
       })
     })
   })
 
-  describe('GET /api/user/:name/repos', function(){
-    describe('without an api key', function(){
-      it('should respond with 400 bad request', function(done){
+  describe('GET /api/user/:name/repos', () => {
+    describe('without an api key', () => {
+      it('should respond with 400 bad request', (done) => {
         request(app)
-        .get('/api/user/loki/repos')
-        .expect(400, done);
+          .get('/api/user/loki/repos')
+          .expect(400, done)
       })
     })
 
-    describe('with an invalid api key', function(){
-      it('should respond with 401 unauthorized', function(done){
+    describe('with an invalid api key', () => {
+      it('should respond with 401 unauthorized', (done) => {
         request(app)
-        .get('/api/user/loki/repos?api-key=rawr')
-        .expect(401, done);
+          .get('/api/user/loki/repos?api-key=rawr')
+          .expect(401, done)
       })
     })
 
-    describe('with a valid api key', function(){
-      it('should respond user repos json', function(done){
+    describe('with a valid api key', () => {
+      it('should respond user repos json', (done) => {
         request(app)
-        .get('/api/user/loki/repos?api-key=foo')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(/"name":"stylus"/)
-        .expect(/"url":"https:\/\/github.com\/learnboost\/stylus"/)
-        .expect(200, done)
+          .get('/api/user/loki/repos?api-key=foo')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(/"name":"stylus"/)
+          .expect(/"url":"https:\/\/github.com\/learnboost\/stylus"/)
+          .expect(200, done)
       })
 
-      it('should 404 with unknown user', function(done){
+      it('should 404 with unknown user', (done) => {
         request(app)
-        .get('/api/user/bob/repos?api-key=foo')
-        .expect(404, done)
+          .get('/api/user/bob/repos?api-key=foo')
+          .expect(404, done)
       })
     })
   })
 
-  describe('when requesting an invalid route', function(){
-    it('should respond with 404 json', function(done){
+  describe('when requesting an invalid route', () => {
+    it('should respond with 404 json', (done) => {
       request(app)
         .get('/api/something?api-key=bar')
         .expect('Content-Type', /json/)
diff --git a/test/app.all.js b/test/app.all.js
index e4afca7d731..caaa38262c5 100644
--- a/test/app.all.js
+++ b/test/app.all.js
@@ -1,17 +1,17 @@
 'use strict'
 
-var after = require('after')
-var express = require('../')
-  , request = require('supertest');
+const after = require('after')
+const express = require('../')
+const request = require('supertest')
 
-describe('app.all()', function(){
-  it('should add a router per method', function(done){
-    var app = express();
-    var cb = after(2, done)
+describe('app.all()', () => {
+  it('should add a router per method', (done) => {
+    const app = express()
+    const cb = after(2, done)
 
-    app.all('/tobi', function(req, res){
-      res.end(req.method);
-    });
+    app.all('/tobi', (req, res) => {
+      res.end(req.method)
+    })
 
     request(app)
       .put('/tobi')
@@ -22,17 +22,17 @@ describe('app.all()', function(){
       .expect(200, 'GET', cb)
   })
 
-  it('should run the callback for a method just once', function(done){
-    var app = express()
-      , n = 0;
+  it('should run the callback for a method just once', (done) => {
+    const app = express()
+    let n = 0
 
-    app.all('/*splat', function(req, res, next){
-      if (n++) return done(new Error('DELETE called several times'));
-      next();
-    });
+    app.all('/*splat', (req, res, next) => {
+      if (n++) return done(new Error('DELETE called several times'))
+      next()
+    })
 
     request(app)
-    .del('/tobi')
-    .expect(404, done);
+      .del('/tobi')
+      .expect(404, done)
   })
 })
diff --git a/test/app.engine.js b/test/app.engine.js
index b0553aa247e..6927751f6e7 100644
--- a/test/app.engine.js
+++ b/test/app.engine.js
@@ -1,82 +1,82 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('../')
-  , fs = require('node:fs');
-var path = require('node:path')
+const assert = require('node:assert')
+const express = require('../')
+const fs = require('node:fs')
+const path = require('node:path')
 
-function render(path, options, fn) {
-  fs.readFile(path, 'utf8', function(err, str){
-    if (err) return fn(err);
-    str = str.replace('{{user.name}}', options.user.name);
-    fn(null, str);
-  });
+function render (path, options, fn) {
+  fs.readFile(path, 'utf8', (err, str) => {
+    if (err) return fn(err)
+    str = str.replace('{{user.name}}', options.user.name)
+    fn(null, str)
+  })
 }
 
-describe('app', function(){
-  describe('.engine(ext, fn)', function(){
-    it('should map a template engine', function(done){
-      var app = express();
+describe('app', () => {
+  describe('.engine(ext, fn)', () => {
+    it('should map a template engine', (done) => {
+      const app = express()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.engine('.html', render);
-      app.locals.user = { name: 'tobi' };
+      app.engine('.html', render)
+      app.locals.user = { name: 'tobi' }
 
-      app.render('user.html', function(err, str){
-        if (err) return done(err);
+      app.render('user.html', (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>tobi</p>')
-        done();
+        done()
       })
     })
 
-    it('should throw when the callback is missing', function(){
-      var app = express();
-      assert.throws(function () {
-        app.engine('.html', null);
+    it('should throw when the callback is missing', () => {
+      const app = express()
+      assert.throws(() => {
+        app.engine('.html', null)
       }, /callback function required/)
     })
 
-    it('should work without leading "."', function(done){
-      var app = express();
+    it('should work without leading "."', (done) => {
+      const app = express()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.engine('html', render);
-      app.locals.user = { name: 'tobi' };
+      app.engine('html', render)
+      app.locals.user = { name: 'tobi' }
 
-      app.render('user.html', function(err, str){
-        if (err) return done(err);
+      app.render('user.html', (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>tobi</p>')
-        done();
+        done()
       })
     })
 
-    it('should work "view engine" setting', function(done){
-      var app = express();
+    it('should work "view engine" setting', (done) => {
+      const app = express()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.engine('html', render);
-      app.set('view engine', 'html');
-      app.locals.user = { name: 'tobi' };
+      app.engine('html', render)
+      app.set('view engine', 'html')
+      app.locals.user = { name: 'tobi' }
 
-      app.render('user', function(err, str){
-        if (err) return done(err);
+      app.render('user', (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>tobi</p>')
-        done();
+        done()
       })
     })
 
-    it('should work "view engine" with leading "."', function(done){
-      var app = express();
+    it('should work "view engine" with leading "."', (done) => {
+      const app = express()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.engine('.html', render);
-      app.set('view engine', '.html');
-      app.locals.user = { name: 'tobi' };
+      app.engine('.html', render)
+      app.set('view engine', '.html')
+      app.locals.user = { name: 'tobi' }
 
-      app.render('user', function(err, str){
-        if (err) return done(err);
+      app.render('user', (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>tobi</p>')
-        done();
+        done()
       })
     })
   })
diff --git a/test/app.head.js b/test/app.head.js
index 0207caaedad..cc3f9309f2c 100644
--- a/test/app.head.js
+++ b/test/app.head.js
@@ -1,62 +1,62 @@
 'use strict'
 
-var express = require('../');
-var request = require('supertest');
-var assert = require('node:assert');
+const express = require('../')
+const request = require('supertest')
+const assert = require('node:assert')
 
-describe('HEAD', function(){
-  it('should default to GET', function(done){
-    var app = express();
+describe('HEAD', () => {
+  it('should default to GET', (done) => {
+    const app = express()
 
-    app.get('/tobi', function(req, res){
+    app.get('/tobi', (req, res) => {
       // send() detects HEAD
-      res.send('tobi');
-    });
+      res.send('tobi')
+    })
 
     request(app)
-    .head('/tobi')
-    .expect(200, done);
+      .head('/tobi')
+      .expect(200, done)
   })
 
-  it('should output the same headers as GET requests', function(done){
-    var app = express();
+  it('should output the same headers as GET requests', (done) => {
+    const app = express()
 
-    app.get('/tobi', function(req, res){
+    app.get('/tobi', (req, res) => {
       // send() detects HEAD
-      res.send('tobi');
-    });
+      res.send('tobi')
+    })
 
     request(app)
-    .head('/tobi')
-    .expect(200, function(err, res){
-      if (err) return done(err);
-      var headers = res.headers;
-      request(app)
-      .get('/tobi')
-      .expect(200, function(err, res){
-        if (err) return done(err);
-        delete headers.date;
-        delete res.headers.date;
-        assert.deepEqual(res.headers, headers);
-        done();
-      });
-    });
+      .head('/tobi')
+      .expect(200, (err, res) => {
+        if (err) return done(err)
+        const headers = res.headers
+        request(app)
+          .get('/tobi')
+          .expect(200, (err, res) => {
+            if (err) return done(err)
+            delete headers.date
+            delete res.headers.date
+            assert.deepEqual(res.headers, headers)
+            done()
+          })
+      })
   })
 })
 
-describe('app.head()', function(){
-  it('should override', function(done){
-    var app = express()
+describe('app.head()', () => {
+  it('should override', (done) => {
+    const app = express()
 
-    app.head('/tobi', function(req, res){
+    app.head('/tobi', (req, res) => {
       res.header('x-method', 'head')
       res.end()
-    });
+    })
 
-    app.get('/tobi', function(req, res){
+    app.get('/tobi', (req, res) => {
       res.header('x-method', 'get')
-      res.send('tobi');
-    });
+      res.send('tobi')
+    })
 
     request(app)
       .head('/tobi')
diff --git a/test/app.js b/test/app.js
index c1e815a052d..1f0c694e265 100644
--- a/test/app.js
+++ b/test/app.js
@@ -1,53 +1,53 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('..')
-var request = require('supertest')
-
-describe('app', function(){
-  it('should inherit from event emitter', function(done){
-    var app = express();
-    app.on('foo', done);
-    app.emit('foo');
+const assert = require('node:assert')
+const express = require('../')
+const request = require('supertest')
+
+describe('app', () => {
+  it('should inherit from event emitter', (done) => {
+    const app = express()
+    app.on('foo', done)
+    app.emit('foo')
   })
 
-  it('should be callable', function(){
-    var app = express();
-    assert.equal(typeof app, 'function');
+  it('should be callable', () => {
+    const app = express()
+    assert.equal(typeof app, 'function')
   })
 
-  it('should 404 without routes', function(done){
+  it('should 404 without routes', (done) => {
     request(express())
-    .get('/')
-    .expect(404, done);
+      .get('/')
+      .expect(404, done)
   })
 })
 
-describe('app.parent', function(){
-  it('should return the parent when mounted', function(){
-    var app = express()
-      , blog = express()
-      , blogAdmin = express();
+describe('app.parent', () => {
+  it('should return the parent when mounted', () => {
+    const app = express()
+    const blog = express()
+    const blogAdmin = express()
 
-    app.use('/blog', blog);
-    blog.use('/admin', blogAdmin);
+    app.use('/blog', blog)
+    blog.use('/admin', blogAdmin)
 
-    assert(!app.parent, 'app.parent');
+    assert(!app.parent, 'app.parent')
     assert.strictEqual(blog.parent, app)
     assert.strictEqual(blogAdmin.parent, blog)
   })
 })
 
-describe('app.mountpath', function(){
-  it('should return the mounted path', function(){
-    var admin = express();
-    var app = express();
-    var blog = express();
-    var fallback = express();
+describe('app.mountpath', () => {
+  it('should return the mounted path', () => {
+    const admin = express()
+    const app = express()
+    const blog = express()
+    const fallback = express()
 
-    app.use('/blog', blog);
-    app.use(fallback);
-    blog.use('/admin', admin);
+    app.use('/blog', blog)
+    app.use(fallback)
+    blog.use('/admin', admin)
 
     assert.strictEqual(admin.mountpath, '/admin')
     assert.strictEqual(app.mountpath, '/')
@@ -56,14 +56,14 @@ describe('app.mountpath', function(){
   })
 })
 
-describe('app.path()', function(){
-  it('should return the canonical', function(){
-    var app = express()
-      , blog = express()
-      , blogAdmin = express();
+describe('app.path()', () => {
+  it('should return the canonical', () => {
+    const app = express()
+    const blog = express()
+    const blogAdmin = express()
 
-    app.use('/blog', blog);
-    blog.use('/admin', blogAdmin);
+    app.use('/blog', blog)
+    blog.use('/admin', blogAdmin)
 
     assert.strictEqual(app.path(), '')
     assert.strictEqual(blog.path(), '/blog')
@@ -71,7 +71,7 @@ describe('app.path()', function(){
   })
 })
 
-describe('in development', function(){
+describe('in development', () => {
   before(function () {
     this.env = process.env.NODE_ENV
     process.env.NODE_ENV = 'development'
@@ -81,13 +81,13 @@ describe('in development', function(){
     process.env.NODE_ENV = this.env
   })
 
-  it('should disable "view cache"', function(){
-    var app = express();
+  it('should disable "view cache"', () => {
+    const app = express()
     assert.ok(!app.enabled('view cache'))
   })
 })
 
-describe('in production', function(){
+describe('in production', () => {
   before(function () {
     this.env = process.env.NODE_ENV
     process.env.NODE_ENV = 'production'
@@ -97,13 +97,13 @@ describe('in production', function(){
     process.env.NODE_ENV = this.env
   })
 
-  it('should enable "view cache"', function(){
-    var app = express();
+  it('should enable "view cache"', () => {
+    const app = express()
     assert.ok(app.enabled('view cache'))
   })
 })
 
-describe('without NODE_ENV', function(){
+describe('without NODE_ENV', () => {
   before(function () {
     this.env = process.env.NODE_ENV
     process.env.NODE_ENV = ''
@@ -113,8 +113,8 @@ describe('without NODE_ENV', function(){
     process.env.NODE_ENV = this.env
   })
 
-  it('should default to development', function(){
-    var app = express();
+  it('should default to development', () => {
+    const app = express()
     assert.strictEqual(app.get('env'), 'development')
   })
 })
diff --git a/test/app.listen.js b/test/app.listen.js
index 3ef94ff184a..a0481edc65f 100644
--- a/test/app.listen.js
+++ b/test/app.listen.js
@@ -1,55 +1,55 @@
 'use strict'
 
-var express = require('../')
-var assert = require('node:assert')
+const express = require('../')
+const assert = require('node:assert')
 
-describe('app.listen()', function(){
-  it('should wrap with an HTTP server', function(done){
-    var app = express();
+describe('app.listen()', () => {
+  it('should wrap with an HTTP server', (done) => {
+    const app = express()
 
-    var server = app.listen(0, function () {
+    const server = app.listen(0, () => {
       server.close(done)
-    });
+    })
   })
-  it('should callback on HTTP server errors', function (done) {
-    var app1 = express()
-    var app2 = express()
+  it('should callback on HTTP server errors', (done) => {
+    const app1 = express()
+    const app2 = express()
 
-    var server1 = app1.listen(0, function (err) {
+    const server1 = app1.listen(0, (err) => {
       assert(!err)
-      app2.listen(server1.address().port, function (err) {
+      app2.listen(server1.address().port, (err) => {
         assert(err.code === 'EADDRINUSE')
         server1.close()
         done()
       })
     })
   })
-  it('accepts port + hostname + backlog + callback', function (done) {
-    const app = express();
-    const server = app.listen(0, '127.0.0.1', 5, function () {
-      const { address, port } = server.address();
-      assert.strictEqual(address, '127.0.0.1');
-      assert(Number.isInteger(port) && port > 0);
+  it('accepts port + hostname + backlog + callback', (done) => {
+    const app = express()
+    const server = app.listen(0, '127.0.0.1', 5, () => {
+      const { address, port } = server.address()
+      assert.strictEqual(address, '127.0.0.1')
+      assert(Number.isInteger(port) && port > 0)
       // backlog isn’t directly inspectable, but if no error was thrown
       // we know it was accepted.
-      server.close(done);
-    });
-  });
-  it('accepts just a callback (no args)', function (done) {
-    const app = express();
+      server.close(done)
+    })
+  })
+  it('accepts just a callback (no args)', (done) => {
+    const app = express()
     // same as app.listen(0, done)
-    const server = app.listen();
-    server.close(done);
-  });
-  it('server.address() gives a { address, port, family } object', function (done) {
-    const app = express();
+    const server = app.listen()
+    server.close(done)
+  })
+  it('server.address() gives a { address, port, family } object', (done) => {
+    const app = express()
     const server = app.listen(0, () => {
-      const addr = server.address();
-      assert(addr && typeof addr === 'object');
-      assert.strictEqual(typeof addr.address, 'string');
-      assert(Number.isInteger(addr.port) && addr.port > 0);
-      assert(typeof addr.family === 'string');
-      server.close(done);
-    });
-  });
+      const addr = server.address()
+      assert(addr && typeof addr === 'object')
+      assert.strictEqual(typeof addr.address, 'string')
+      assert(Number.isInteger(addr.port) && addr.port > 0)
+      assert(typeof addr.family === 'string')
+      server.close(done)
+    })
+  })
 })
diff --git a/test/app.locals.js b/test/app.locals.js
index 3963762fe2b..5a848e9fc18 100644
--- a/test/app.locals.js
+++ b/test/app.locals.js
@@ -1,20 +1,20 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('../')
+const assert = require('node:assert')
+const express = require('../')
 
-describe('app', function(){
-  describe('.locals', function () {
-    it('should default object with null prototype', function () {
-      var app = express()
+describe('app', () => {
+  describe('.locals', () => {
+    it('should default object with null prototype', () => {
+      const app = express()
       assert.ok(app.locals)
       assert.strictEqual(typeof app.locals, 'object')
       assert.strictEqual(Object.getPrototypeOf(app.locals), null)
     })
 
-    describe('.settings', function () {
-      it('should contain app settings ', function () {
-        var app = express()
+    describe('.settings', () => {
+      it('should contain app settings ', () => {
+        const app = express()
         app.set('title', 'Express')
         assert.ok(app.locals.settings)
         assert.strictEqual(typeof app.locals.settings, 'object')
diff --git a/test/app.options.js b/test/app.options.js
index ee4c81631cb..9f3d8a73f9e 100644
--- a/test/app.options.js
+++ b/test/app.options.js
@@ -1,116 +1,116 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('OPTIONS', function(){
-  it('should default to the routes defined', function(done){
-    var app = express();
+describe('OPTIONS', () => {
+  it('should default to the routes defined', (done) => {
+    const app = express()
 
-    app.post('/', function(){});
-    app.get('/users', function(req, res){});
-    app.put('/users', function(req, res){});
+    app.post('/', () => {})
+    app.get('/users', (req, res) => {})
+    app.put('/users', (req, res) => {})
 
     request(app)
-    .options('/users')
-    .expect('Allow', 'GET, HEAD, PUT')
-    .expect(200, 'GET, HEAD, PUT', done);
+      .options('/users')
+      .expect('Allow', 'GET, HEAD, PUT')
+      .expect(200, 'GET, HEAD, PUT', done)
   })
 
-  it('should only include each method once', function(done){
-    var app = express();
+  it('should only include each method once', (done) => {
+    const app = express()
 
-    app.delete('/', function(){});
-    app.get('/users', function(req, res){});
-    app.put('/users', function(req, res){});
-    app.get('/users', function(req, res){});
+    app.delete('/', () => {})
+    app.get('/users', (req, res) => {})
+    app.put('/users', (req, res) => {})
+    app.get('/users', (req, res) => {})
 
     request(app)
-    .options('/users')
-    .expect('Allow', 'GET, HEAD, PUT')
-    .expect(200, 'GET, HEAD, PUT', done);
+      .options('/users')
+      .expect('Allow', 'GET, HEAD, PUT')
+      .expect(200, 'GET, HEAD, PUT', done)
   })
 
-  it('should not be affected by app.all', function(done){
-    var app = express();
+  it('should not be affected by app.all', (done) => {
+    const app = express()
 
-    app.get('/', function(){});
-    app.get('/users', function(req, res){});
-    app.put('/users', function(req, res){});
-    app.all('/users', function(req, res, next){
-      res.setHeader('x-hit', '1');
-      next();
-    });
+    app.get('/', () => {})
+    app.get('/users', (req, res) => {})
+    app.put('/users', (req, res) => {})
+    app.all('/users', (req, res, next) => {
+      res.setHeader('x-hit', '1')
+      next()
+    })
 
     request(app)
-    .options('/users')
-    .expect('x-hit', '1')
-    .expect('Allow', 'GET, HEAD, PUT')
-    .expect(200, 'GET, HEAD, PUT', done);
+      .options('/users')
+      .expect('x-hit', '1')
+      .expect('Allow', 'GET, HEAD, PUT')
+      .expect(200, 'GET, HEAD, PUT', done)
   })
 
-  it('should not respond if the path is not defined', function(done){
-    var app = express();
+  it('should not respond if the path is not defined', (done) => {
+    const app = express()
 
-    app.get('/users', function(req, res){});
+    app.get('/users', (req, res) => {})
 
     request(app)
-    .options('/other')
-    .expect(404, done);
+      .options('/other')
+      .expect(404, done)
   })
 
-  it('should forward requests down the middleware chain', function(done){
-    var app = express();
-    var router = new express.Router();
+  it('should forward requests down the middleware chain', (done) => {
+    const app = express()
+    const router = new express.Router()
 
-    router.get('/users', function(req, res){});
-    app.use(router);
-    app.get('/other', function(req, res){});
+    router.get('/users', (req, res) => {})
+    app.use(router)
+    app.get('/other', (req, res) => {})
 
     request(app)
-    .options('/other')
-    .expect('Allow', 'GET, HEAD')
-    .expect(200, 'GET, HEAD', done);
+      .options('/other')
+      .expect('Allow', 'GET, HEAD')
+      .expect(200, 'GET, HEAD', done)
   })
 
-  describe('when error occurs in response handler', function () {
-    it('should pass error to callback', function (done) {
-      var app = express();
-      var router = express.Router();
+  describe('when error occurs in response handler', () => {
+    it('should pass error to callback', (done) => {
+      const app = express()
+      const router = express.Router()
 
-      router.get('/users', function(req, res){});
+      router.get('/users', (req, res) => {})
 
-      app.use(function (req, res, next) {
-        res.writeHead(200);
-        next();
-      });
-      app.use(router);
-      app.use(function (err, req, res, next) {
-        res.end('true');
-      });
+      app.use((req, res, next) => {
+        res.writeHead(200)
+        next()
+      })
+      app.use(router)
+      app.use((err, req, res, next) => {
+        res.end('true')
+      })
 
       request(app)
-      .options('/users')
-      .expect(200, 'true', done)
+        .options('/users')
+        .expect(200, 'true', done)
     })
   })
 })
 
-describe('app.options()', function(){
-  it('should override the default behavior', function(done){
-    var app = express();
+describe('app.options()', () => {
+  it('should override the default behavior', (done) => {
+    const app = express()
 
-    app.options('/users', function(req, res){
-      res.set('Allow', 'GET');
-      res.send('GET');
-    });
+    app.options('/users', (req, res) => {
+      res.set('Allow', 'GET')
+      res.send('GET')
+    })
 
-    app.get('/users', function(req, res){});
-    app.put('/users', function(req, res){});
+    app.get('/users', (req, res) => {})
+    app.put('/users', (req, res) => {})
 
     request(app)
-    .options('/users')
-    .expect('GET')
-    .expect('Allow', 'GET', done);
+      .options('/users')
+      .expect('GET')
+      .expect('Allow', 'GET', done)
   })
 })
diff --git a/test/app.param.js b/test/app.param.js
index 5c9a5630870..602bb33f737 100644
--- a/test/app.param.js
+++ b/test/app.param.js
@@ -1,33 +1,33 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
-
-describe('app', function(){
-  describe('.param(names, fn)', function(){
-    it('should map the array', function(done){
-      var app = express();
-
-      app.param(['id', 'uid'], function(req, res, next, id){
-        id = Number(id);
-        if (isNaN(id)) return next('route');
-        req.params.id = id;
-        next();
-      });
-
-      app.get('/post/:id', function(req, res){
-        var id = req.params.id;
+const express = require('../')
+const request = require('supertest')
+
+describe('app', () => {
+  describe('.param(names, fn)', () => {
+    it('should map the array', (done) => {
+      const app = express()
+
+      app.param(['id', 'uid'], (req, res, next, id) => {
+        id = Number(id)
+        if (isNaN(id)) return next('route')
+        req.params.id = id
+        next()
+      })
+
+      app.get('/post/:id', (req, res) => {
+        const id = req.params.id
         res.send((typeof id) + ':' + id)
-      });
+      })
 
-      app.get('/user/:uid', function(req, res){
-        var id = req.params.id;
+      app.get('/user/:uid', (req, res) => {
+        const id = req.params.id
         res.send((typeof id) + ':' + id)
-      });
+      })
 
       request(app)
         .get('/user/123')
-        .expect(200, 'number:123', function (err) {
+        .expect(200, 'number:123', (err) => {
           if (err) return done(err)
           request(app)
             .get('/post/123')
@@ -36,288 +36,288 @@ describe('app', function(){
     })
   })
 
-  describe('.param(name, fn)', function(){
-    it('should map logic for a single param', function(done){
-      var app = express();
+  describe('.param(name, fn)', () => {
+    it('should map logic for a single param', (done) => {
+      const app = express()
 
-      app.param('id', function(req, res, next, id){
-        id = Number(id);
-        if (isNaN(id)) return next('route');
-        req.params.id = id;
-        next();
-      });
+      app.param('id', (req, res, next, id) => {
+        id = Number(id)
+        if (isNaN(id)) return next('route')
+        req.params.id = id
+        next()
+      })
 
-      app.get('/user/:id', function(req, res){
-        var id = req.params.id;
+      app.get('/user/:id', (req, res) => {
+        const id = req.params.id
         res.send((typeof id) + ':' + id)
-      });
+      })
 
       request(app)
         .get('/user/123')
         .expect(200, 'number:123', done)
     })
 
-    it('should only call once per request', function(done) {
-      var app = express();
-      var called = 0;
-      var count = 0;
-
-      app.param('user', function(req, res, next, user) {
-        called++;
-        req.user = user;
-        next();
-      });
-
-      app.get('/foo/:user', function(req, res, next) {
-        count++;
-        next();
-      });
-      app.get('/foo/:user', function(req, res, next) {
-        count++;
-        next();
-      });
-      app.use(function(req, res) {
-        res.end([count, called, req.user].join(' '));
-      });
+    it('should only call once per request', (done) => {
+      const app = express()
+      let called = 0
+      let count = 0
+
+      app.param('user', (req, res, next, user) => {
+        called++
+        req.user = user
+        next()
+      })
+
+      app.get('/foo/:user', (req, res, next) => {
+        count++
+        next()
+      })
+      app.get('/foo/:user', (req, res, next) => {
+        count++
+        next()
+      })
+      app.use((req, res) => {
+        res.end([count, called, req.user].join(' '))
+      })
 
       request(app)
-      .get('/foo/bob')
-      .expect('2 1 bob', done);
+        .get('/foo/bob')
+        .expect('2 1 bob', done)
     })
 
-    it('should call when values differ', function(done) {
-      var app = express();
-      var called = 0;
-      var count = 0;
-
-      app.param('user', function(req, res, next, user) {
-        called++;
-        req.users = (req.users || []).concat(user);
-        next();
-      });
-
-      app.get('/:user/bob', function(req, res, next) {
-        count++;
-        next();
-      });
-      app.get('/foo/:user', function(req, res, next) {
-        count++;
-        next();
-      });
-      app.use(function(req, res) {
-        res.end([count, called, req.users.join(',')].join(' '));
-      });
+    it('should call when values differ', (done) => {
+      const app = express()
+      let called = 0
+      let count = 0
+
+      app.param('user', (req, res, next, user) => {
+        called++
+        req.users = (req.users || []).concat(user)
+        next()
+      })
+
+      app.get('/:user/bob', (req, res, next) => {
+        count++
+        next()
+      })
+      app.get('/foo/:user', (req, res, next) => {
+        count++
+        next()
+      })
+      app.use((req, res) => {
+        res.end([count, called, req.users.join(',')].join(' '))
+      })
 
       request(app)
-      .get('/foo/bob')
-      .expect('2 2 foo,bob', done);
+        .get('/foo/bob')
+        .expect('2 2 foo,bob', done)
     })
 
-    it('should support altering req.params across routes', function(done) {
-      var app = express();
+    it('should support altering req.params across routes', (done) => {
+      const app = express()
 
-      app.param('user', function(req, res, next, user) {
-        req.params.user = 'loki';
-        next();
-      });
+      app.param('user', (req, res, next, user) => {
+        req.params.user = 'loki'
+        next()
+      })
 
-      app.get('/:user', function(req, res, next) {
-        next('route');
-      });
-      app.get('/:user', function (req, res) {
-        res.send(req.params.user);
-      });
+      app.get('/:user', (req, res, next) => {
+        next('route')
+      })
+      app.get('/:user', (req, res) => {
+        res.send(req.params.user)
+      })
 
       request(app)
-      .get('/bob')
-      .expect('loki', done);
+        .get('/bob')
+        .expect('loki', done)
     })
 
-    it('should not invoke without route handler', function(done) {
-      var app = express();
+    it('should not invoke without route handler', (done) => {
+      const app = express()
 
-      app.param('thing', function(req, res, next, thing) {
-        req.thing = thing;
-        next();
-      });
+      app.param('thing', (req, res, next, thing) => {
+        req.thing = thing
+        next()
+      })
 
-      app.param('user', function(req, res, next, user) {
+      app.param('user', (req, res, next, user) => {
         next(new Error('invalid invocation'))
-      });
+      })
 
-      app.post('/:user', function (req, res) {
-        res.send(req.params.user);
-      });
+      app.post('/:user', (req, res) => {
+        res.send(req.params.user)
+      })
 
-      app.get('/:thing', function (req, res) {
-        res.send(req.thing);
-      });
+      app.get('/:thing', (req, res) => {
+        res.send(req.thing)
+      })
 
       request(app)
-      .get('/bob')
-      .expect(200, 'bob', done);
+        .get('/bob')
+        .expect(200, 'bob', done)
     })
 
-    it('should work with encoded values', function(done){
-      var app = express();
+    it('should work with encoded values', (done) => {
+      const app = express()
 
-      app.param('name', function(req, res, next, name){
-        req.params.name = name;
-        next();
-      });
+      app.param('name', (req, res, next, name) => {
+        req.params.name = name
+        next()
+      })
 
-      app.get('/user/:name', function(req, res){
-        var name = req.params.name;
-        res.send('' + name);
-      });
+      app.get('/user/:name', (req, res) => {
+        const name = req.params.name
+        res.send('' + name)
+      })
 
       request(app)
-      .get('/user/foo%25bar')
-      .expect('foo%bar', done);
+        .get('/user/foo%25bar')
+        .expect('foo%bar', done)
     })
 
-    it('should catch thrown error', function(done){
-      var app = express();
+    it('should catch thrown error', (done) => {
+      const app = express()
 
-      app.param('id', function(req, res, next, id){
-        throw new Error('err!');
-      });
+      app.param('id', (req, res, next, id) => {
+        throw new Error('err!')
+      })
 
-      app.get('/user/:id', function(req, res){
-        var id = req.params.id;
-        res.send('' + id);
-      });
+      app.get('/user/:id', (req, res) => {
+        const id = req.params.id
+        res.send('' + id)
+      })
 
       request(app)
-      .get('/user/123')
-      .expect(500, done);
+        .get('/user/123')
+        .expect(500, done)
     })
 
-    it('should catch thrown secondary error', function(done){
-      var app = express();
+    it('should catch thrown secondary error', (done) => {
+      const app = express()
 
-      app.param('id', function(req, res, next, val){
-        process.nextTick(next);
-      });
+      app.param('id', (req, res, next, val) => {
+        process.nextTick(next)
+      })
 
-      app.param('id', function(req, res, next, id){
-        throw new Error('err!');
-      });
+      app.param('id', (req, res, next, id) => {
+        throw new Error('err!')
+      })
 
-      app.get('/user/:id', function(req, res){
-        var id = req.params.id;
-        res.send('' + id);
-      });
+      app.get('/user/:id', (req, res) => {
+        const id = req.params.id
+        res.send('' + id)
+      })
 
       request(app)
-      .get('/user/123')
-      .expect(500, done);
+        .get('/user/123')
+        .expect(500, done)
     })
 
-    it('should defer to next route', function(done){
-      var app = express();
+    it('should defer to next route', (done) => {
+      const app = express()
 
-      app.param('id', function(req, res, next, id){
-        next('route');
-      });
+      app.param('id', (req, res, next, id) => {
+        next('route')
+      })
 
-      app.get('/user/:id', function(req, res){
-        var id = req.params.id;
-        res.send('' + id);
-      });
+      app.get('/user/:id', (req, res) => {
+        const id = req.params.id
+        res.send('' + id)
+      })
 
-      app.get('/:name/123', function(req, res){
-        res.send('name');
-      });
+      app.get('/:name/123', (req, res) => {
+        res.send('name')
+      })
 
       request(app)
-      .get('/user/123')
-      .expect('name', done);
+        .get('/user/123')
+        .expect('name', done)
     })
 
-    it('should defer all the param routes', function(done){
-      var app = express();
+    it('should defer all the param routes', (done) => {
+      const app = express()
 
-      app.param('id', function(req, res, next, val){
-        if (val === 'new') return next('route');
-        return next();
-      });
+      app.param('id', (req, res, next, val) => {
+        if (val === 'new') return next('route')
+        return next()
+      })
 
-      app.all('/user/:id', function(req, res){
-        res.send('all.id');
-      });
+      app.all('/user/:id', (req, res) => {
+        res.send('all.id')
+      })
 
-      app.get('/user/:id', function(req, res){
-        res.send('get.id');
-      });
+      app.get('/user/:id', (req, res) => {
+        res.send('get.id')
+      })
 
-      app.get('/user/new', function(req, res){
-        res.send('get.new');
-      });
+      app.get('/user/new', (req, res) => {
+        res.send('get.new')
+      })
 
       request(app)
-      .get('/user/new')
-      .expect('get.new', done);
+        .get('/user/new')
+        .expect('get.new', done)
     })
 
-    it('should not call when values differ on error', function(done) {
-      var app = express();
-      var called = 0;
-      var count = 0;
-
-      app.param('user', function(req, res, next, user) {
-        called++;
-        if (user === 'foo') throw new Error('err!');
-        req.user = user;
-        next();
-      });
-
-      app.get('/:user/bob', function(req, res, next) {
-        count++;
-        next();
-      });
-      app.get('/foo/:user', function(req, res, next) {
-        count++;
-        next();
-      });
-
-      app.use(function(err, req, res, next) {
-        res.status(500);
-        res.send([count, called, err.message].join(' '));
-      });
+    it('should not call when values differ on error', (done) => {
+      const app = express()
+      let called = 0
+      let count = 0
+
+      app.param('user', (req, res, next, user) => {
+        called++
+        if (user === 'foo') throw new Error('err!')
+        req.user = user
+        next()
+      })
+
+      app.get('/:user/bob', (req, res, next) => {
+        count++
+        next()
+      })
+      app.get('/foo/:user', (req, res, next) => {
+        count++
+        next()
+      })
+
+      app.use((err, req, res, next) => {
+        res.status(500)
+        res.send([count, called, err.message].join(' '))
+      })
 
       request(app)
-      .get('/foo/bob')
-      .expect(500, '0 1 err!', done)
-    });
-
-    it('should call when values differ when using "next"', function(done) {
-      var app = express();
-      var called = 0;
-      var count = 0;
-
-      app.param('user', function(req, res, next, user) {
-        called++;
-        if (user === 'foo') return next('route');
-        req.user = user;
-        next();
-      });
-
-      app.get('/:user/bob', function(req, res, next) {
-        count++;
-        next();
-      });
-      app.get('/foo/:user', function(req, res, next) {
-        count++;
-        next();
-      });
-      app.use(function(req, res) {
-        res.end([count, called, req.user].join(' '));
-      });
+        .get('/foo/bob')
+        .expect(500, '0 1 err!', done)
+    })
+
+    it('should call when values differ when using "next"', (done) => {
+      const app = express()
+      let called = 0
+      let count = 0
+
+      app.param('user', (req, res, next, user) => {
+        called++
+        if (user === 'foo') return next('route')
+        req.user = user
+        next()
+      })
+
+      app.get('/:user/bob', (req, res, next) => {
+        count++
+        next()
+      })
+      app.get('/foo/:user', (req, res, next) => {
+        count++
+        next()
+      })
+      app.use((req, res) => {
+        res.end([count, called, req.user].join(' '))
+      })
 
       request(app)
-      .get('/foo/bob')
-      .expect('1 2 bob', done);
+        .get('/foo/bob')
+        .expect('1 2 bob', done)
     })
   })
 })
diff --git a/test/app.render.js b/test/app.render.js
index ca15e761d35..8d1a804e2c6 100644
--- a/test/app.render.js
+++ b/test/app.render.js
@@ -1,104 +1,104 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('..');
-var path = require('node:path')
-var tmpl = require('./support/tmpl');
+const assert = require('node:assert')
+const express = require('../')
+const path = require('node:path')
+const tmpl = require('./support/tmpl')
 
-describe('app', function(){
-  describe('.render(name, fn)', function(){
-    it('should support absolute paths', function(done){
-      var app = createApp();
+describe('app', () => {
+  describe('.render(name, fn)', () => {
+    it('should support absolute paths', (done) => {
+      const app = createApp()
 
-      app.locals.user = { name: 'tobi' };
+      app.locals.user = { name: 'tobi' }
 
-      app.render(path.join(__dirname, 'fixtures', 'user.tmpl'), function (err, str) {
-        if (err) return done(err);
+      app.render(path.join(__dirname, 'fixtures', 'user.tmpl'), (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>tobi</p>')
-        done();
+        done()
       })
     })
 
-    it('should support absolute paths with "view engine"', function(done){
-      var app = createApp();
+    it('should support absolute paths with "view engine"', (done) => {
+      const app = createApp()
 
-      app.set('view engine', 'tmpl');
-      app.locals.user = { name: 'tobi' };
+      app.set('view engine', 'tmpl')
+      app.locals.user = { name: 'tobi' }
 
-      app.render(path.join(__dirname, 'fixtures', 'user'), function (err, str) {
-        if (err) return done(err);
+      app.render(path.join(__dirname, 'fixtures', 'user'), (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>tobi</p>')
-        done();
+        done()
       })
     })
 
-    it('should expose app.locals', function(done){
-      var app = createApp();
+    it('should expose app.locals', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.locals.user = { name: 'tobi' };
+      app.locals.user = { name: 'tobi' }
 
-      app.render('user.tmpl', function (err, str) {
-        if (err) return done(err);
+      app.render('user.tmpl', (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>tobi</p>')
-        done();
+        done()
       })
     })
 
-    it('should support index.<engine>', function(done){
-      var app = createApp();
+    it('should support index.<engine>', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.set('view engine', 'tmpl');
+      app.set('view engine', 'tmpl')
 
-      app.render('blog/post', function (err, str) {
-        if (err) return done(err);
+      app.render('blog/post', (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<h1>blog post</h1>')
-        done();
+        done()
       })
     })
 
-    it('should handle render error throws', function(done){
-      var app = express();
+    it('should handle render error throws', (done) => {
+      const app = express()
 
-      function View(name, options){
-        this.name = name;
-        this.path = 'fale';
+      function View (name, options) {
+        this.name = name
+        this.path = 'fale'
       }
 
-      View.prototype.render = function(options, fn){
-        throw new Error('err!');
-      };
+      View.prototype.render = function (options, fn) {
+        throw new Error('err!')
+      }
 
-      app.set('view', View);
+      app.set('view', View)
 
-      app.render('something', function(err, str){
+      app.render('something', (err, str) => {
         assert.ok(err)
         assert.strictEqual(err.message, 'err!')
-        done();
+        done()
       })
     })
 
-    describe('when the file does not exist', function(){
-      it('should provide a helpful error', function(done){
-        var app = createApp();
+    describe('when the file does not exist', () => {
+      it('should provide a helpful error', (done) => {
+        const app = createApp()
 
         app.set('views', path.join(__dirname, 'fixtures'))
-        app.render('rawr.tmpl', function (err) {
+        app.render('rawr.tmpl', (err) => {
           assert.ok(err)
           assert.equal(err.message, 'Failed to lookup view "rawr.tmpl" in views directory "' + path.join(__dirname, 'fixtures') + '"')
-          done();
-        });
+          done()
+        })
       })
     })
 
-    describe('when an error occurs', function(){
-      it('should invoke the callback', function(done){
-        var app = createApp();
+    describe('when an error occurs', () => {
+      it('should invoke the callback', (done) => {
+        const app = createApp()
 
         app.set('views', path.join(__dirname, 'fixtures'))
 
-        app.render('user.tmpl', function (err) {
+        app.render('user.tmpl', (err) => {
           assert.ok(err)
           assert.equal(err.name, 'RenderError')
           done()
@@ -106,258 +106,258 @@ describe('app', function(){
       })
     })
 
-    describe('when an extension is given', function(){
-      it('should render the template', function(done){
-        var app = createApp();
+    describe('when an extension is given', () => {
+      it('should render the template', (done) => {
+        const app = createApp()
 
         app.set('views', path.join(__dirname, 'fixtures'))
 
-        app.render('email.tmpl', function (err, str) {
-          if (err) return done(err);
+        app.render('email.tmpl', (err, str) => {
+          if (err) return done(err)
           assert.strictEqual(str, '<p>This is an email</p>')
-          done();
+          done()
         })
       })
     })
 
-    describe('when "view engine" is given', function(){
-      it('should render the template', function(done){
-        var app = createApp();
+    describe('when "view engine" is given', () => {
+      it('should render the template', (done) => {
+        const app = createApp()
 
-        app.set('view engine', 'tmpl');
+        app.set('view engine', 'tmpl')
         app.set('views', path.join(__dirname, 'fixtures'))
 
-        app.render('email', function(err, str){
-          if (err) return done(err);
+        app.render('email', (err, str) => {
+          if (err) return done(err)
           assert.strictEqual(str, '<p>This is an email</p>')
-          done();
+          done()
         })
       })
     })
 
-    describe('when "views" is given', function(){
-      it('should lookup the file in the path', function(done){
-        var app = createApp();
+    describe('when "views" is given', () => {
+      it('should lookup the file in the path', (done) => {
+        const app = createApp()
 
-        app.set('views',  path.join(__dirname, 'fixtures', 'default_layout'))
-        app.locals.user = { name: 'tobi' };
+        app.set('views', path.join(__dirname, 'fixtures', 'default_layout'))
+        app.locals.user = { name: 'tobi' }
 
-        app.render('user.tmpl', function (err, str) {
-          if (err) return done(err);
+        app.render('user.tmpl', (err, str) => {
+          if (err) return done(err)
           assert.strictEqual(str, '<p>tobi</p>')
-          done();
+          done()
         })
       })
 
-      describe('when array of paths', function(){
-        it('should lookup the file in the path', function(done){
-          var app = createApp();
-          var views = [
+      describe('when array of paths', () => {
+        it('should lookup the file in the path', (done) => {
+          const app = createApp()
+          const views = [
             path.join(__dirname, 'fixtures', 'local_layout'),
             path.join(__dirname, 'fixtures', 'default_layout')
           ]
 
-          app.set('views', views);
-          app.locals.user = { name: 'tobi' };
+          app.set('views', views)
+          app.locals.user = { name: 'tobi' }
 
-          app.render('user.tmpl', function (err, str) {
-            if (err) return done(err);
+          app.render('user.tmpl', (err, str) => {
+            if (err) return done(err)
             assert.strictEqual(str, '<span>tobi</span>')
-            done();
+            done()
           })
         })
 
-        it('should lookup in later paths until found', function(done){
-          var app = createApp();
-          var views = [
+        it('should lookup in later paths until found', (done) => {
+          const app = createApp()
+          const views = [
             path.join(__dirname, 'fixtures', 'local_layout'),
             path.join(__dirname, 'fixtures', 'default_layout')
           ]
 
-          app.set('views', views);
-          app.locals.name = 'tobi';
+          app.set('views', views)
+          app.locals.name = 'tobi'
 
-          app.render('name.tmpl', function (err, str) {
-            if (err) return done(err);
+          app.render('name.tmpl', (err, str) => {
+            if (err) return done(err)
             assert.strictEqual(str, '<p>tobi</p>')
-            done();
+            done()
           })
         })
 
-        it('should error if file does not exist', function(done){
-          var app = createApp();
-          var views = [
+        it('should error if file does not exist', (done) => {
+          const app = createApp()
+          const views = [
             path.join(__dirname, 'fixtures', 'local_layout'),
             path.join(__dirname, 'fixtures', 'default_layout')
           ]
 
-          app.set('views', views);
-          app.locals.name = 'tobi';
+          app.set('views', views)
+          app.locals.name = 'tobi'
 
-          app.render('pet.tmpl', function (err, str) {
+          app.render('pet.tmpl', (err, str) => {
             assert.ok(err)
             assert.equal(err.message, 'Failed to lookup view "pet.tmpl" in views directories "' + views[0] + '" or "' + views[1] + '"')
-            done();
+            done()
           })
         })
       })
     })
 
-    describe('when a "view" constructor is given', function(){
-      it('should create an instance of it', function(done){
-        var app = express();
+    describe('when a "view" constructor is given', () => {
+      it('should create an instance of it', (done) => {
+        const app = express()
 
-        function View(name, options){
-          this.name = name;
-          this.path = 'path is required by application.js as a signal of success even though it is not used there.';
+        function View (name, options) {
+          this.name = name
+          this.path = 'path is required by application.js as a signal of success even though it is not used there.'
         }
 
-        View.prototype.render = function(options, fn){
-          fn(null, 'abstract engine');
-        };
+        View.prototype.render = function (options, fn) {
+          fn(null, 'abstract engine')
+        }
 
-        app.set('view', View);
+        app.set('view', View)
 
-        app.render('something', function(err, str){
-          if (err) return done(err);
+        app.render('something', (err, str) => {
+          if (err) return done(err)
           assert.strictEqual(str, 'abstract engine')
-          done();
+          done()
         })
       })
     })
 
-    describe('caching', function(){
-      it('should always lookup view without cache', function(done){
-        var app = express();
-        var count = 0;
+    describe('caching', () => {
+      it('should always lookup view without cache', (done) => {
+        const app = express()
+        let count = 0
 
-        function View(name, options){
-          this.name = name;
-          this.path = 'fake';
-          count++;
+        function View (name, options) {
+          this.name = name
+          this.path = 'fake'
+          count++
         }
 
-        View.prototype.render = function(options, fn){
-          fn(null, 'abstract engine');
-        };
+        View.prototype.render = function (options, fn) {
+          fn(null, 'abstract engine')
+        }
 
-        app.set('view cache', false);
-        app.set('view', View);
+        app.set('view cache', false)
+        app.set('view', View)
 
-        app.render('something', function(err, str){
-          if (err) return done(err);
+        app.render('something', (err, str) => {
+          if (err) return done(err)
           assert.strictEqual(count, 1)
           assert.strictEqual(str, 'abstract engine')
-          app.render('something', function(err, str){
-            if (err) return done(err);
+          app.render('something', (err, str) => {
+            if (err) return done(err)
             assert.strictEqual(count, 2)
             assert.strictEqual(str, 'abstract engine')
-            done();
+            done()
           })
         })
       })
 
-      it('should cache with "view cache" setting', function(done){
-        var app = express();
-        var count = 0;
+      it('should cache with "view cache" setting', (done) => {
+        const app = express()
+        let count = 0
 
-        function View(name, options){
-          this.name = name;
-          this.path = 'fake';
-          count++;
+        function View (name, options) {
+          this.name = name
+          this.path = 'fake'
+          count++
         }
 
-        View.prototype.render = function(options, fn){
-          fn(null, 'abstract engine');
-        };
+        View.prototype.render = function (options, fn) {
+          fn(null, 'abstract engine')
+        }
 
-        app.set('view cache', true);
-        app.set('view', View);
+        app.set('view cache', true)
+        app.set('view', View)
 
-        app.render('something', function(err, str){
-          if (err) return done(err);
+        app.render('something', (err, str) => {
+          if (err) return done(err)
           assert.strictEqual(count, 1)
           assert.strictEqual(str, 'abstract engine')
-          app.render('something', function(err, str){
-            if (err) return done(err);
+          app.render('something', (err, str) => {
+            if (err) return done(err)
             assert.strictEqual(count, 1)
             assert.strictEqual(str, 'abstract engine')
-            done();
+            done()
           })
         })
       })
     })
   })
 
-  describe('.render(name, options, fn)', function(){
-    it('should render the template', function(done){
-      var app = createApp();
+  describe('.render(name, options, fn)', () => {
+    it('should render the template', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
 
-      var user = { name: 'tobi' };
+      const user = { name: 'tobi' }
 
-      app.render('user.tmpl', { user: user }, function (err, str) {
-        if (err) return done(err);
+      app.render('user.tmpl', { user }, (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>tobi</p>')
-        done();
+        done()
       })
     })
 
-    it('should expose app.locals', function(done){
-      var app = createApp();
+    it('should expose app.locals', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.locals.user = { name: 'tobi' };
+      app.locals.user = { name: 'tobi' }
 
-      app.render('user.tmpl', {}, function (err, str) {
-        if (err) return done(err);
+      app.render('user.tmpl', {}, (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>tobi</p>')
-        done();
+        done()
       })
     })
 
-    it('should give precedence to app.render() locals', function(done){
-      var app = createApp();
+    it('should give precedence to app.render() locals', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.locals.user = { name: 'tobi' };
-      var jane = { name: 'jane' };
+      app.locals.user = { name: 'tobi' }
+      const jane = { name: 'jane' }
 
-      app.render('user.tmpl', { user: jane }, function (err, str) {
-        if (err) return done(err);
+      app.render('user.tmpl', { user: jane }, (err, str) => {
+        if (err) return done(err)
         assert.strictEqual(str, '<p>jane</p>')
-        done();
+        done()
       })
     })
 
-    describe('caching', function(){
-      it('should cache with cache option', function(done){
-        var app = express();
-        var count = 0;
+    describe('caching', () => {
+      it('should cache with cache option', (done) => {
+        const app = express()
+        let count = 0
 
-        function View(name, options){
-          this.name = name;
-          this.path = 'fake';
-          count++;
+        function View (name, options) {
+          this.name = name
+          this.path = 'fake'
+          count++
         }
 
-        View.prototype.render = function(options, fn){
-          fn(null, 'abstract engine');
-        };
+        View.prototype.render = function (options, fn) {
+          fn(null, 'abstract engine')
+        }
 
-        app.set('view cache', false);
-        app.set('view', View);
+        app.set('view cache', false)
+        app.set('view', View)
 
-        app.render('something', {cache: true}, function(err, str){
-          if (err) return done(err);
+        app.render('something', { cache: true }, (err, str) => {
+          if (err) return done(err)
           assert.strictEqual(count, 1)
           assert.strictEqual(str, 'abstract engine')
-          app.render('something', {cache: true}, function(err, str){
-            if (err) return done(err);
+          app.render('something', { cache: true }, (err, str) => {
+            if (err) return done(err)
             assert.strictEqual(count, 1)
             assert.strictEqual(str, 'abstract engine')
-            done();
+            done()
           })
         })
       })
@@ -365,10 +365,10 @@ describe('app', function(){
   })
 })
 
-function createApp() {
-  var app = express();
+function createApp () {
+  const app = express()
 
-  app.engine('.tmpl', tmpl);
+  app.engine('.tmpl', tmpl)
 
-  return app;
+  return app
 }
diff --git a/test/app.request.js b/test/app.request.js
index b6c00f5baa3..71cd862105e 100644
--- a/test/app.request.js
+++ b/test/app.request.js
@@ -1,41 +1,41 @@
 'use strict'
 
-var after = require('after')
-var express = require('../')
-  , request = require('supertest');
+const after = require('after')
+const express = require('../')
+const request = require('supertest')
 
-describe('app', function(){
-  describe('.request', function(){
-    it('should extend the request prototype', function(done){
-      var app = express();
+describe('app', () => {
+  describe('.request', () => {
+    it('should extend the request prototype', (done) => {
+      const app = express()
 
-      app.request.querystring = function(){
-        return require('node:url').parse(this.url).query;
-      };
+      app.request.querystring = function () {
+        return (new URL(this.url)).query
+      }
 
-      app.use(function(req, res){
-        res.end(req.querystring());
-      });
+      app.use((req, res) => {
+        res.end(req.querystring())
+      })
 
       request(app)
-      .get('/foo?name=tobi')
-      .expect('name=tobi', done);
+        .get('/foo?name=tobi')
+        .expect('name=tobi', done)
     })
 
-    it('should only extend for the referenced app', function (done) {
-      var app1 = express()
-      var app2 = express()
-      var cb = after(2, done)
+    it('should only extend for the referenced app', (done) => {
+      const app1 = express()
+      const app2 = express()
+      const cb = after(2, done)
 
       app1.request.foobar = function () {
         return 'tobi'
       }
 
-      app1.get('/', function (req, res) {
+      app1.get('/', (req, res) => {
         res.send(req.foobar())
       })
 
-      app2.get('/', function (req, res) {
+      app2.get('/', (req, res) => {
         res.send(req.foobar())
       })
 
@@ -48,10 +48,10 @@ describe('app', function(){
         .expect(500, /(?:not a function|has no method)/, cb)
     })
 
-    it('should inherit to sub apps', function (done) {
-      var app1 = express()
-      var app2 = express()
-      var cb = after(2, done)
+    it('should inherit to sub apps', (done) => {
+      const app1 = express()
+      const app2 = express()
+      const cb = after(2, done)
 
       app1.request.foobar = function () {
         return 'tobi'
@@ -59,11 +59,11 @@ describe('app', function(){
 
       app1.use('/sub', app2)
 
-      app1.get('/', function (req, res) {
+      app1.get('/', (req, res) => {
         res.send(req.foobar())
       })
 
-      app2.get('/', function (req, res) {
+      app2.get('/', (req, res) => {
         res.send(req.foobar())
       })
 
@@ -76,10 +76,10 @@ describe('app', function(){
         .expect(200, 'tobi', cb)
     })
 
-    it('should allow sub app to override', function (done) {
-      var app1 = express()
-      var app2 = express()
-      var cb = after(2, done)
+    it('should allow sub app to override', (done) => {
+      const app1 = express()
+      const app2 = express()
+      const cb = after(2, done)
 
       app1.request.foobar = function () {
         return 'tobi'
@@ -91,11 +91,11 @@ describe('app', function(){
 
       app1.use('/sub', app2)
 
-      app1.get('/', function (req, res) {
+      app1.get('/', (req, res) => {
         res.send(req.foobar())
       })
 
-      app2.get('/', function (req, res) {
+      app2.get('/', (req, res) => {
         res.send(req.foobar())
       })
 
@@ -108,10 +108,10 @@ describe('app', function(){
         .expect(200, 'loki', cb)
     })
 
-    it('should not pollute parent app', function (done) {
-      var app1 = express()
-      var app2 = express()
-      var cb = after(2, done)
+    it('should not pollute parent app', (done) => {
+      const app1 = express()
+      const app2 = express()
+      const cb = after(2, done)
 
       app1.request.foobar = function () {
         return 'tobi'
@@ -123,11 +123,11 @@ describe('app', function(){
 
       app1.use('/sub', app2)
 
-      app1.get('/sub/foo', function (req, res) {
+      app1.get('/sub/foo', (req, res) => {
         res.send(req.foobar())
       })
 
-      app2.get('/', function (req, res) {
+      app2.get('/', (req, res) => {
         res.send(req.foobar())
       })
 
diff --git a/test/app.response.js b/test/app.response.js
index 5fb69f6275a..98cb40339eb 100644
--- a/test/app.response.js
+++ b/test/app.response.js
@@ -1,41 +1,41 @@
 'use strict'
 
-var after = require('after')
-var express = require('../')
-  , request = require('supertest');
+const after = require('after')
+const express = require('../')
+const request = require('supertest')
 
-describe('app', function(){
-  describe('.response', function(){
-    it('should extend the response prototype', function(done){
-      var app = express();
+describe('app', () => {
+  describe('.response', () => {
+    it('should extend the response prototype', (done) => {
+      const app = express()
 
-      app.response.shout = function(str){
-        this.send(str.toUpperCase());
-      };
+      app.response.shout = function (str) {
+        this.send(str.toUpperCase())
+      }
 
-      app.use(function(req, res){
-        res.shout('hey');
-      });
+      app.use((req, res) => {
+        res.shout('hey')
+      })
 
       request(app)
-      .get('/')
-      .expect('HEY', done);
+        .get('/')
+        .expect('HEY', done)
     })
 
-    it('should only extend for the referenced app', function (done) {
-      var app1 = express()
-      var app2 = express()
-      var cb = after(2, done)
+    it('should only extend for the referenced app', (done) => {
+      const app1 = express()
+      const app2 = express()
+      const cb = after(2, done)
 
       app1.response.shout = function (str) {
         this.send(str.toUpperCase())
       }
 
-      app1.get('/', function (req, res) {
+      app1.get('/', (req, res) => {
         res.shout('foo')
       })
 
-      app2.get('/', function (req, res) {
+      app2.get('/', (req, res) => {
         res.shout('foo')
       })
 
@@ -48,10 +48,10 @@ describe('app', function(){
         .expect(500, /(?:not a function|has no method)/, cb)
     })
 
-    it('should inherit to sub apps', function (done) {
-      var app1 = express()
-      var app2 = express()
-      var cb = after(2, done)
+    it('should inherit to sub apps', (done) => {
+      const app1 = express()
+      const app2 = express()
+      const cb = after(2, done)
 
       app1.response.shout = function (str) {
         this.send(str.toUpperCase())
@@ -59,11 +59,11 @@ describe('app', function(){
 
       app1.use('/sub', app2)
 
-      app1.get('/', function (req, res) {
+      app1.get('/', (req, res) => {
         res.shout('foo')
       })
 
-      app2.get('/', function (req, res) {
+      app2.get('/', (req, res) => {
         res.shout('foo')
       })
 
@@ -76,10 +76,10 @@ describe('app', function(){
         .expect(200, 'FOO', cb)
     })
 
-    it('should allow sub app to override', function (done) {
-      var app1 = express()
-      var app2 = express()
-      var cb = after(2, done)
+    it('should allow sub app to override', (done) => {
+      const app1 = express()
+      const app2 = express()
+      const cb = after(2, done)
 
       app1.response.shout = function (str) {
         this.send(str.toUpperCase())
@@ -91,11 +91,11 @@ describe('app', function(){
 
       app1.use('/sub', app2)
 
-      app1.get('/', function (req, res) {
+      app1.get('/', (req, res) => {
         res.shout('foo')
       })
 
-      app2.get('/', function (req, res) {
+      app2.get('/', (req, res) => {
         res.shout('foo')
       })
 
@@ -108,10 +108,10 @@ describe('app', function(){
         .expect(200, 'foo!', cb)
     })
 
-    it('should not pollute parent app', function (done) {
-      var app1 = express()
-      var app2 = express()
-      var cb = after(2, done)
+    it('should not pollute parent app', (done) => {
+      const app1 = express()
+      const app2 = express()
+      const cb = after(2, done)
 
       app1.response.shout = function (str) {
         this.send(str.toUpperCase())
@@ -123,11 +123,11 @@ describe('app', function(){
 
       app1.use('/sub', app2)
 
-      app1.get('/sub/foo', function (req, res) {
+      app1.get('/sub/foo', (req, res) => {
         res.shout('foo')
       })
 
-      app2.get('/', function (req, res) {
+      app2.get('/', (req, res) => {
         res.shout('foo')
       })
 
diff --git a/test/app.route.js b/test/app.route.js
index 03ae1293685..71d8a82d7b5 100644
--- a/test/app.route.js
+++ b/test/app.route.js
@@ -1,197 +1,189 @@
 'use strict'
 
-var express = require('../');
-var request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('app.route', function(){
-  it('should return a new route', function(done){
-    var app = express();
+describe('app.route', () => {
+  it('should return a new route', (done) => {
+    const app = express()
 
     app.route('/foo')
-    .get(function(req, res) {
-      res.send('get');
-    })
-    .post(function(req, res) {
-      res.send('post');
-    });
+      .get((req, res) => {
+        res.send('get')
+      })
+      .post((req, res) => {
+        res.send('post')
+      })
 
     request(app)
-    .post('/foo')
-    .expect('post', done);
-  });
+      .post('/foo')
+      .expect('post', done)
+  })
 
-  it('should all .VERB after .all', function(done){
-    var app = express();
+  it('should all .VERB after .all', (done) => {
+    const app = express()
 
     app.route('/foo')
-    .all(function(req, res, next) {
-      next();
-    })
-    .get(function(req, res) {
-      res.send('get');
-    })
-    .post(function(req, res) {
-      res.send('post');
-    });
+      .all((req, res, next) => {
+        next()
+      })
+      .get((req, res) => {
+        res.send('get')
+      })
+      .post((req, res) => {
+        res.send('post')
+      })
 
     request(app)
-    .post('/foo')
-    .expect('post', done);
-  });
+      .post('/foo')
+      .expect('post', done)
+  })
 
-  it('should support dynamic routes', function(done){
-    var app = express();
+  it('should support dynamic routes', (done) => {
+    const app = express()
 
     app.route('/:foo')
-    .get(function(req, res) {
-      res.send(req.params.foo);
-    });
+      .get((req, res) => {
+        res.send(req.params.foo)
+      })
 
     request(app)
-    .get('/test')
-    .expect('test', done);
-  });
+      .get('/test')
+      .expect('test', done)
+  })
 
-  it('should not error on empty routes', function(done){
-    var app = express();
+  it('should not error on empty routes', (done) => {
+    const app = express()
 
-    app.route('/:foo');
+    app.route('/:foo')
 
     request(app)
-    .get('/test')
-    .expect(404, done);
-  });
+      .get('/test')
+      .expect(404, done)
+  })
 
-  describe('promise support', function () {
-    it('should pass rejected promise value', function (done) {
-      var app = express()
-      var route = app.route('/foo')
+  describe('promise support', () => {
+    it('should pass rejected promise value', (done) => {
+      const app = express()
+      const route = app.route('/foo')
 
-      route.all(function createError (req, res, next) {
-        return Promise.reject(new Error('boom!'))
-      })
+      route.all((req, res, next) => Promise.reject(new Error('boom!')))
 
-      route.all(function helloWorld (req, res) {
+      route.all((req, res) => {
         res.send('hello, world!')
       })
 
-      route.all(function handleError (err, req, res, next) {
+      route.all((err, req, res, next) => {
         res.status(500)
         res.send('caught: ' + err.message)
       })
 
       request(app)
-      .get('/foo')
-      .expect(500, 'caught: boom!', done)
+        .get('/foo')
+        .expect(500, 'caught: boom!', done)
     })
 
-    it('should pass rejected promise without value', function (done) {
-      var app = express()
-      var route = app.route('/foo')
+    it('should pass rejected promise without value', (done) => {
+      const app = express()
+      const route = app.route('/foo')
 
-      route.all(function createError (req, res, next) {
-        return Promise.reject()
-      })
+      route.all((req, res, next) =>
+        // eslint-disable-next-line prefer-promise-reject-errors
+        Promise.reject()
+      )
 
-      route.all(function helloWorld (req, res) {
+      route.all((req, res) => {
         res.send('hello, world!')
       })
 
-      route.all(function handleError (err, req, res, next) {
+      route.all((err, req, res, next) => {
         res.status(500)
         res.send('caught: ' + err.message)
       })
 
       request(app)
-      .get('/foo')
-      .expect(500, 'caught: Rejected promise', done)
+        .get('/foo')
+        .expect(500, 'caught: Rejected promise', done)
     })
 
-    it('should ignore resolved promise', function (done) {
-      var app = express()
-      var route = app.route('/foo')
+    it('should ignore resolved promise', (done) => {
+      const app = express()
+      const route = app.route('/foo')
 
-      route.all(function createError (req, res, next) {
+      route.all((req, res, next) => {
         res.send('saw GET /foo')
         return Promise.resolve('foo')
       })
 
-      route.all(function () {
+      route.all(() => {
         done(new Error('Unexpected route invoke'))
       })
 
       request(app)
-      .get('/foo')
-      .expect(200, 'saw GET /foo', done)
+        .get('/foo')
+        .expect(200, 'saw GET /foo', done)
     })
 
-    describe('error handling', function () {
-      it('should pass rejected promise value', function (done) {
-        var app = express()
-        var route = app.route('/foo')
+    describe('error handling', () => {
+      it('should pass rejected promise value', (done) => {
+        const app = express()
+        const route = app.route('/foo')
 
-        route.all(function createError (req, res, next) {
-          return Promise.reject(new Error('boom!'))
-        })
+        route.all((req, res, next) => Promise.reject(new Error('boom!')))
 
-        route.all(function handleError (err, req, res, next) {
-          return Promise.reject(new Error('caught: ' + err.message))
-        })
+        route.all((err, req, res, next) => Promise.reject(new Error('caught: ' + err.message)))
 
-        route.all(function handleError (err, req, res, next) {
+        route.all((err, req, res, next) => {
           res.status(500)
           res.send('caught again: ' + err.message)
         })
 
         request(app)
-        .get('/foo')
-        .expect(500, 'caught again: caught: boom!', done)
+          .get('/foo')
+          .expect(500, 'caught again: caught: boom!', done)
       })
 
-      it('should pass rejected promise without value', function (done) {
-        var app = express()
-        var route = app.route('/foo')
+      it('should pass rejected promise without value', (done) => {
+        const app = express()
+        const route = app.route('/foo')
 
-        route.all(function createError (req, res, next) {
-          return Promise.reject(new Error('boom!'))
-        })
+        route.all((req, res, next) => Promise.reject(new Error('boom!')))
 
-        route.all(function handleError (err, req, res, next) {
-          return Promise.reject()
-        })
+        route.all((err, req, res, next) =>
+          // eslint-disable-next-line prefer-promise-reject-errors
+          Promise.reject()
+        )
 
-        route.all(function handleError (err, req, res, next) {
+        route.all((err, req, res, next) => {
           res.status(500)
           res.send('caught again: ' + err.message)
         })
 
         request(app)
-        .get('/foo')
-        .expect(500, 'caught again: Rejected promise', done)
+          .get('/foo')
+          .expect(500, 'caught again: Rejected promise', done)
       })
 
-      it('should ignore resolved promise', function (done) {
-        var app = express()
-        var route = app.route('/foo')
+      it('should ignore resolved promise', (done) => {
+        const app = express()
+        const route = app.route('/foo')
 
-        route.all(function createError (req, res, next) {
-          return Promise.reject(new Error('boom!'))
-        })
+        route.all((req, res, next) => Promise.reject(new Error('boom!')))
 
-        route.all(function handleError (err, req, res, next) {
+        route.all((err, req, res, next) => {
           res.status(500)
           res.send('caught: ' + err.message)
           return Promise.resolve('foo')
         })
 
-        route.all(function () {
+        route.all(() => {
           done(new Error('Unexpected route invoke'))
         })
 
         request(app)
-        .get('/foo')
-        .expect(500, 'caught: boom!', done)
+          .get('/foo')
+          .expect(500, 'caught: boom!', done)
       })
     })
   })
-});
+})
diff --git a/test/app.router.js b/test/app.router.js
index 6e7be684e55..d181a3219dc 100644
--- a/test/app.router.js
+++ b/test/app.router.js
@@ -1,80 +1,79 @@
 'use strict'
 
-var after = require('after');
-var express = require('../')
-  , request = require('supertest')
-  , assert = require('node:assert')
-  , methods = require('../lib/utils').methods;
+const after = require('after')
+const express = require('../')
+const request = require('supertest')
+const assert = require('node:assert')
+const { methods } = require('../lib/utils')
 
-var shouldSkipQuery = require('./support/utils').shouldSkipQuery
+const { shouldSkipQuery } = require('./support/utils')
 
-describe('app.router', function () {
-  it('should restore req.params after leaving router', function (done) {
-    var app = express();
-    var router = new express.Router();
+describe('app.router', () => {
+  it('should restore req.params after leaving router', (done) => {
+    const app = express()
+    const router = new express.Router()
 
-    function handler1(req, res, next) {
-      res.setHeader('x-user-id', String(req.params.id));
+    function handler1 (req, res, next) {
+      res.setHeader('x-user-id', String(req.params.id))
       next()
     }
 
-    function handler2(req, res) {
-      res.send(req.params.id);
+    function handler2 (req, res) {
+      res.send(req.params.id)
     }
 
-    router.use(function (req, res, next) {
-      res.setHeader('x-router', String(req.params.id));
-      next();
-    });
+    router.use((req, res, next) => {
+      res.setHeader('x-router', String(req.params.id))
+      next()
+    })
 
-    app.get('/user/:id', handler1, router, handler2);
+    app.get('/user/:id', handler1, router, handler2)
 
     request(app)
       .get('/user/1')
       .expect('x-router', 'undefined')
       .expect('x-user-id', '1')
-      .expect(200, '1', done);
+      .expect(200, '1', done)
   })
 
-  describe('methods', function () {
-    methods.forEach(function (method) {
-      if (method === 'connect') return;
+  describe('methods', () => {
+    methods.forEach((method) => {
+      if (method === 'connect') return
 
       it('should include ' + method.toUpperCase(), function (done) {
         if (method === 'query' && shouldSkipQuery(process.versions.node)) {
           this.skip()
         }
-        var app = express();
+        const app = express()
 
-        app[method]('/foo', function (req, res) {
+        app[method]('/foo', (req, res) => {
           res.send(method)
-        });
+        })
 
-        request(app)
-        [method]('/foo')
+        request(app)[method]('/foo')
           .expect(200, done)
       })
 
-      it('should reject numbers for app.' + method, function () {
-        var app = express();
-        assert.throws(app[method].bind(app, '/', 3), /argument handler must be a function/);
+      it('should reject numbers for app.' + method, () => {
+        const app = express()
+        assert.throws(app[method].bind(app, '/', 3), /argument handler must be a function/)
       })
-    });
+    })
 
-    it('should re-route when method is altered', function (done) {
-      var app = express();
-      var cb = after(3, done);
+    it('should re-route when method is altered', (done) => {
+      const app = express()
+      const cb = after(3, done)
 
-      app.use(function (req, res, next) {
-        if (req.method !== 'POST') return next();
-        req.method = 'DELETE';
-        res.setHeader('X-Method-Altered', '1');
-        next();
-      });
+      app.use((req, res, next) => {
+        if (req.method !== 'POST') return next()
+        req.method = 'DELETE'
+        res.setHeader('X-Method-Altered', '1')
+        next()
+      })
 
-      app.delete('/', function (req, res) {
-        res.end('deleted everything');
-      });
+      app.delete('/', (req, res) => {
+        res.end('deleted everything')
+      })
 
       request(app)
         .get('/')
@@ -82,157 +81,158 @@ describe('app.router', function () {
 
       request(app)
         .delete('/')
-        .expect(200, 'deleted everything', cb);
+        .expect(200, 'deleted everything', cb)
 
       request(app)
         .post('/')
         .expect('X-Method-Altered', '1')
-        .expect(200, 'deleted everything', cb);
-    });
+        .expect(200, 'deleted everything', cb)
+    })
   })
 
-  describe('decode params', function () {
-    it('should decode correct params', function (done) {
-      var app = express();
+  describe('decode params', () => {
+    it('should decode correct params', (done) => {
+      const app = express()
 
-      app.get('/:name', function (req, res) {
-        res.send(req.params.name);
-      });
+      app.get('/:name', (req, res) => {
+        res.send(req.params.name)
+      })
 
       request(app)
         .get('/foo%2Fbar')
-        .expect('foo/bar', done);
+        .expect('foo/bar', done)
     })
 
-    it('should not accept params in malformed paths', function (done) {
-      var app = express();
+    it('should not accept params in malformed paths', (done) => {
+      const app = express()
 
-      app.get('/:name', function (req, res) {
-        res.send(req.params.name);
-      });
+      app.get('/:name', (req, res) => {
+        res.send(req.params.name)
+      })
 
       request(app)
         .get('/%foobar')
-        .expect(400, done);
+        .expect(400, done)
     })
 
-    it('should not decode spaces', function (done) {
-      var app = express();
+    it('should not decode spaces', (done) => {
+      const app = express()
 
-      app.get('/:name', function (req, res) {
-        res.send(req.params.name);
-      });
+      app.get('/:name', (req, res) => {
+        res.send(req.params.name)
+      })
 
       request(app)
         .get('/foo+bar')
-        .expect('foo+bar', done);
+        .expect('foo+bar', done)
     })
 
-    it('should work with unicode', function (done) {
-      var app = express();
+    it('should work with unicode', (done) => {
+      const app = express()
 
-      app.get('/:name', function (req, res) {
-        res.send(req.params.name);
-      });
+      app.get('/:name', (req, res) => {
+        res.send(req.params.name)
+      })
 
       request(app)
         .get('/%ce%b1')
-        .expect('\u03b1', done);
+        .expect('\u03b1', done)
     })
   })
 
-  it('should be .use()able', function (done) {
-    var app = express();
+  it('should be .use()able', (done) => {
+    const app = express()
 
-    var calls = [];
+    const calls = []
 
-    app.use(function (req, res, next) {
-      calls.push('before');
-      next();
-    });
+    app.use((req, res, next) => {
+      calls.push('before')
+      next()
+    })
 
-    app.get('/', function (req, res, next) {
+    app.get('/', (req, res, next) => {
       calls.push('GET /')
-      next();
-    });
+      next()
+    })
 
-    app.use(function (req, res, next) {
-      calls.push('after');
+    app.use((req, res, next) => {
+      calls.push('after')
       res.json(calls)
-    });
+    })
 
     request(app)
       .get('/')
       .expect(200, ['before', 'GET /', 'after'], done)
   })
 
-  describe('when given a regexp', function () {
-    it('should match the pathname only', function (done) {
-      var app = express();
+  describe('when given a regexp', () => {
+    it('should match the pathname only', (done) => {
+      const app = express()
 
-      app.get(/^\/user\/[0-9]+$/, function (req, res) {
-        res.end('user');
-      });
+      app.get(/^\/user\/[0-9]+$/, (req, res) => {
+        res.end('user')
+      })
 
       request(app)
         .get('/user/12?foo=bar')
-        .expect('user', done);
+        .expect('user', done)
     })
 
-    it('should populate req.params with the captures', function (done) {
-      var app = express();
+    it('should populate req.params with the captures', (done) => {
+      const app = express()
 
-      app.get(/^\/user\/([0-9]+)\/(view|edit)?$/, function (req, res) {
-        var id = req.params[0]
-          , op = req.params[1];
-        res.end(op + 'ing user ' + id);
-      });
+      app.get(/^\/user\/([0-9]+)\/(view|edit)?$/, (req, res) => {
+        const id = req.params[0]
+        const op = req.params[1]
+        res.end(op + 'ing user ' + id)
+      })
 
       request(app)
         .get('/user/10/edit')
-        .expect('editing user 10', done);
+        .expect('editing user 10', done)
     })
 
     if (supportsRegexp('(?<foo>.*)')) {
-      it('should populate req.params with named captures', function (done) {
-        var app = express();
-        var re = new RegExp('^/user/(?<userId>[0-9]+)/(view|edit)?$');
-
-        app.get(re, function (req, res) {
-          var id = req.params.userId
-            , op = req.params[0];
-          res.end(op + 'ing user ' + id);
-        });
+      it('should populate req.params with named captures', (done) => {
+        const app = express()
+        // eslint-disable-next-line prefer-regex-literals
+        const re = new RegExp('^/user/(?<userId>[0-9]+)/(view|edit)?$')
+
+        app.get(re, (req, res) => {
+          const id = req.params.userId
+          const op = req.params[0]
+          res.end(op + 'ing user ' + id)
+        })
 
         request(app)
           .get('/user/10/edit')
-          .expect('editing user 10', done);
+          .expect('editing user 10', done)
       })
     }
 
-    it('should ensure regexp matches path prefix', function (done) {
-      var app = express()
-      var p = []
+    it('should ensure regexp matches path prefix', (done) => {
+      const app = express()
+      const p = []
 
-      app.use(/\/api.*/, function (req, res, next) {
+      app.use(/\/api.*/, (req, res, next) => {
         p.push('a')
         next()
       })
-      app.use(/api/, function (req, res, next) {
+      app.use(/api/, (req, res, next) => {
         p.push('b')
         next()
       })
-      app.use(/\/test/, function (req, res, next) {
+      app.use(/\/test/, (req, res, next) => {
         p.push('c')
         next()
       })
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.end()
       })
 
       request(app)
         .get('/test/api/1234')
-        .expect(200, function (err) {
+        .expect(200, (err) => {
           if (err) return done(err)
           assert.deepEqual(p, ['c'])
           done()
@@ -240,472 +240,472 @@ describe('app.router', function () {
     })
   })
 
-  describe('case sensitivity', function () {
-    it('should be disabled by default', function (done) {
-      var app = express();
+  describe('case sensitivity', () => {
+    it('should be disabled by default', (done) => {
+      const app = express()
 
-      app.get('/user', function (req, res) {
-        res.end('tj');
-      });
+      app.get('/user', (req, res) => {
+        res.end('tj')
+      })
 
       request(app)
         .get('/USER')
-        .expect('tj', done);
+        .expect('tj', done)
     })
 
-    describe('when "case sensitive routing" is enabled', function () {
-      it('should match identical casing', function (done) {
-        var app = express();
+    describe('when "case sensitive routing" is enabled', () => {
+      it('should match identical casing', (done) => {
+        const app = express()
 
-        app.enable('case sensitive routing');
+        app.enable('case sensitive routing')
 
-        app.get('/uSer', function (req, res) {
-          res.end('tj');
-        });
+        app.get('/uSer', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/uSer')
-          .expect('tj', done);
+          .expect('tj', done)
       })
 
-      it('should not match otherwise', function (done) {
-        var app = express();
+      it('should not match otherwise', (done) => {
+        const app = express()
 
-        app.enable('case sensitive routing');
+        app.enable('case sensitive routing')
 
-        app.get('/uSer', function (req, res) {
-          res.end('tj');
-        });
+        app.get('/uSer', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user')
-          .expect(404, done);
+          .expect(404, done)
       })
     })
   })
 
-  describe('params', function () {
-    it('should overwrite existing req.params by default', function (done) {
-      var app = express();
-      var router = new express.Router();
+  describe('params', () => {
+    it('should overwrite existing req.params by default', (done) => {
+      const app = express()
+      const router = new express.Router()
 
-      router.get('/:action', function (req, res) {
-        res.send(req.params);
-      });
+      router.get('/:action', (req, res) => {
+        res.send(req.params)
+      })
 
-      app.use('/user/:user', router);
+      app.use('/user/:user', router)
 
       request(app)
         .get('/user/1/get')
-        .expect(200, '{"action":"get"}', done);
+        .expect(200, '{"action":"get"}', done)
     })
 
-    it('should allow merging existing req.params', function (done) {
-      var app = express();
-      var router = new express.Router({ mergeParams: true });
+    it('should allow merging existing req.params', (done) => {
+      const app = express()
+      const router = new express.Router({ mergeParams: true })
 
-      router.get('/:action', function (req, res) {
-        var keys = Object.keys(req.params).sort();
-        res.send(keys.map(function (k) { return [k, req.params[k]] }));
-      });
+      router.get('/:action', (req, res) => {
+        const keys = Object.keys(req.params).sort()
+        res.send(keys.map((k) => [k, req.params[k]]))
+      })
 
-      app.use('/user/:user', router);
+      app.use('/user/:user', router)
 
       request(app)
         .get('/user/tj/get')
-        .expect(200, '[["action","get"],["user","tj"]]', done);
+        .expect(200, '[["action","get"],["user","tj"]]', done)
     })
 
-    it('should use params from router', function (done) {
-      var app = express();
-      var router = new express.Router({ mergeParams: true });
+    it('should use params from router', (done) => {
+      const app = express()
+      const router = new express.Router({ mergeParams: true })
 
-      router.get('/:thing', function (req, res) {
-        var keys = Object.keys(req.params).sort();
-        res.send(keys.map(function (k) { return [k, req.params[k]] }));
-      });
+      router.get('/:thing', (req, res) => {
+        const keys = Object.keys(req.params).sort()
+        res.send(keys.map((k) => [k, req.params[k]]))
+      })
 
-      app.use('/user/:thing', router);
+      app.use('/user/:thing', router)
 
       request(app)
         .get('/user/tj/get')
-        .expect(200, '[["thing","get"]]', done);
+        .expect(200, '[["thing","get"]]', done)
     })
 
-    it('should merge numeric indices req.params', function (done) {
-      var app = express();
-      var router = new express.Router({ mergeParams: true });
+    it('should merge numeric indices req.params', (done) => {
+      const app = express()
+      const router = new express.Router({ mergeParams: true })
 
-      router.get(/^\/(.*)\.(.*)/, function (req, res) {
-        var keys = Object.keys(req.params).sort();
-        res.send(keys.map(function (k) { return [k, req.params[k]] }));
-      });
+      router.get(/^\/(.*)\.(.*)/, (req, res) => {
+        const keys = Object.keys(req.params).sort()
+        res.send(keys.map((k) => [k, req.params[k]]))
+      })
 
-      app.use(/^\/user\/id:(\d+)/, router);
+      app.use(/^\/user\/id:(\d+)/, router)
 
       request(app)
         .get('/user/id:10/profile.json')
-        .expect(200, '[["0","10"],["1","profile"],["2","json"]]', done);
+        .expect(200, '[["0","10"],["1","profile"],["2","json"]]', done)
     })
 
-    it('should merge numeric indices req.params when more in parent', function (done) {
-      var app = express();
-      var router = new express.Router({ mergeParams: true });
+    it('should merge numeric indices req.params when more in parent', (done) => {
+      const app = express()
+      const router = new express.Router({ mergeParams: true })
 
-      router.get(/\/(.*)/, function (req, res) {
-        var keys = Object.keys(req.params).sort();
-        res.send(keys.map(function (k) { return [k, req.params[k]] }));
-      });
+      router.get(/\/(.*)/, (req, res) => {
+        const keys = Object.keys(req.params).sort()
+        res.send(keys.map((k) => [k, req.params[k]]))
+      })
 
-      app.use(/^\/user\/id:(\d+)\/name:(\w+)/, router);
+      app.use(/^\/user\/id:(\d+)\/name:(\w+)/, router)
 
       request(app)
         .get('/user/id:10/name:tj/profile')
-        .expect(200, '[["0","10"],["1","tj"],["2","profile"]]', done);
+        .expect(200, '[["0","10"],["1","tj"],["2","profile"]]', done)
     })
 
-    it('should merge numeric indices req.params when parent has same number', function (done) {
-      var app = express();
-      var router = new express.Router({ mergeParams: true });
+    it('should merge numeric indices req.params when parent has same number', (done) => {
+      const app = express()
+      const router = new express.Router({ mergeParams: true })
 
-      router.get(/\/name:(\w+)/, function (req, res) {
-        var keys = Object.keys(req.params).sort();
-        res.send(keys.map(function (k) { return [k, req.params[k]] }));
-      });
+      router.get(/\/name:(\w+)/, (req, res) => {
+        const keys = Object.keys(req.params).sort()
+        res.send(keys.map((k) => [k, req.params[k]]))
+      })
 
-      app.use(/\/user\/id:(\d+)/, router);
+      app.use(/\/user\/id:(\d+)/, router)
 
       request(app)
         .get('/user/id:10/name:tj')
-        .expect(200, '[["0","10"],["1","tj"]]', done);
+        .expect(200, '[["0","10"],["1","tj"]]', done)
     })
 
-    it('should ignore invalid incoming req.params', function (done) {
-      var app = express();
-      var router = new express.Router({ mergeParams: true });
+    it('should ignore invalid incoming req.params', (done) => {
+      const app = express()
+      const router = new express.Router({ mergeParams: true })
 
-      router.get('/:name', function (req, res) {
-        var keys = Object.keys(req.params).sort();
-        res.send(keys.map(function (k) { return [k, req.params[k]] }));
-      });
+      router.get('/:name', (req, res) => {
+        const keys = Object.keys(req.params).sort()
+        res.send(keys.map((k) => [k, req.params[k]]))
+      })
 
-      app.use('/user/', function (req, res, next) {
-        req.params = 3; // wat?
-        router(req, res, next);
-      });
+      app.use('/user/', (req, res, next) => {
+        req.params = 3 // wat?
+        router(req, res, next)
+      })
 
       request(app)
         .get('/user/tj')
-        .expect(200, '[["name","tj"]]', done);
+        .expect(200, '[["name","tj"]]', done)
     })
 
-    it('should restore req.params', function (done) {
-      var app = express();
-      var router = new express.Router({ mergeParams: true });
+    it('should restore req.params', (done) => {
+      const app = express()
+      const router = new express.Router({ mergeParams: true })
 
-      router.get(/\/user:(\w+)\//, function (req, res, next) {
-        next();
-      });
+      router.get(/\/user:(\w+)\//, (req, res, next) => {
+        next()
+      })
 
-      app.use(/\/user\/id:(\d+)/, function (req, res, next) {
-        router(req, res, function (err) {
-          var keys = Object.keys(req.params).sort();
-          res.send(keys.map(function (k) { return [k, req.params[k]] }));
-        });
-      });
+      app.use(/\/user\/id:(\d+)/, (req, res, next) => {
+        router(req, res, (err) => {
+          const keys = Object.keys(req.params).sort()
+          res.send(keys.map((k) => [k, req.params[k]]))
+        })
+      })
 
       request(app)
         .get('/user/id:42/user:tj/profile')
-        .expect(200, '[["0","42"]]', done);
+        .expect(200, '[["0","42"]]', done)
     })
   })
 
-  describe('trailing slashes', function () {
-    it('should be optional by default', function (done) {
-      var app = express();
+  describe('trailing slashes', () => {
+    it('should be optional by default', (done) => {
+      const app = express()
 
-      app.get('/user', function (req, res) {
-        res.end('tj');
-      });
+      app.get('/user', (req, res) => {
+        res.end('tj')
+      })
 
       request(app)
         .get('/user/')
-        .expect('tj', done);
+        .expect('tj', done)
     })
 
-    describe('when "strict routing" is enabled', function () {
-      it('should match trailing slashes', function (done) {
-        var app = express();
+    describe('when "strict routing" is enabled', () => {
+      it('should match trailing slashes', (done) => {
+        const app = express()
 
-        app.enable('strict routing');
+        app.enable('strict routing')
 
-        app.get('/user/', function (req, res) {
-          res.end('tj');
-        });
+        app.get('/user/', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user/')
-          .expect('tj', done);
+          .expect('tj', done)
       })
 
-      it('should pass-though middleware', function (done) {
-        var app = express();
+      it('should pass-though middleware', (done) => {
+        const app = express()
 
-        app.enable('strict routing');
+        app.enable('strict routing')
 
-        app.use(function (req, res, next) {
-          res.setHeader('x-middleware', 'true');
-          next();
-        });
+        app.use((req, res, next) => {
+          res.setHeader('x-middleware', 'true')
+          next()
+        })
 
-        app.get('/user/', function (req, res) {
-          res.end('tj');
-        });
+        app.get('/user/', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user/')
           .expect('x-middleware', 'true')
-          .expect(200, 'tj', done);
+          .expect(200, 'tj', done)
       })
 
-      it('should pass-though mounted middleware', function (done) {
-        var app = express();
+      it('should pass-though mounted middleware', (done) => {
+        const app = express()
 
-        app.enable('strict routing');
+        app.enable('strict routing')
 
-        app.use('/user/', function (req, res, next) {
-          res.setHeader('x-middleware', 'true');
-          next();
-        });
+        app.use('/user/', (req, res, next) => {
+          res.setHeader('x-middleware', 'true')
+          next()
+        })
 
-        app.get('/user/test/', function (req, res) {
-          res.end('tj');
-        });
+        app.get('/user/test/', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user/test/')
           .expect('x-middleware', 'true')
-          .expect(200, 'tj', done);
+          .expect(200, 'tj', done)
       })
 
-      it('should match no slashes', function (done) {
-        var app = express();
+      it('should match no slashes', (done) => {
+        const app = express()
 
-        app.enable('strict routing');
+        app.enable('strict routing')
 
-        app.get('/user', function (req, res) {
-          res.end('tj');
-        });
+        app.get('/user', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user')
-          .expect('tj', done);
+          .expect('tj', done)
       })
 
-      it('should match middleware when omitting the trailing slash', function (done) {
-        var app = express();
+      it('should match middleware when omitting the trailing slash', (done) => {
+        const app = express()
 
-        app.enable('strict routing');
+        app.enable('strict routing')
 
-        app.use('/user/', function (req, res) {
-          res.end('tj');
-        });
+        app.use('/user/', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user')
-          .expect(200, 'tj', done);
+          .expect(200, 'tj', done)
       })
 
-      it('should match middleware', function (done) {
-        var app = express();
+      it('should match middleware', (done) => {
+        const app = express()
 
-        app.enable('strict routing');
+        app.enable('strict routing')
 
-        app.use('/user', function (req, res) {
-          res.end('tj');
-        });
+        app.use('/user', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user')
-          .expect(200, 'tj', done);
+          .expect(200, 'tj', done)
       })
 
-      it('should match middleware when adding the trailing slash', function (done) {
-        var app = express();
+      it('should match middleware when adding the trailing slash', (done) => {
+        const app = express()
 
-        app.enable('strict routing');
+        app.enable('strict routing')
 
-        app.use('/user', function (req, res) {
-          res.end('tj');
-        });
+        app.use('/user', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user/')
-          .expect(200, 'tj', done);
+          .expect(200, 'tj', done)
       })
 
-      it('should fail when omitting the trailing slash', function (done) {
-        var app = express();
+      it('should fail when omitting the trailing slash', (done) => {
+        const app = express()
 
-        app.enable('strict routing');
+        app.enable('strict routing')
 
-        app.get('/user/', function (req, res) {
-          res.end('tj');
-        });
+        app.get('/user/', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user')
-          .expect(404, done);
+          .expect(404, done)
       })
 
-      it('should fail when adding the trailing slash', function (done) {
-        var app = express();
+      it('should fail when adding the trailing slash', (done) => {
+        const app = express()
 
-        app.enable('strict routing');
+        app.enable('strict routing')
 
-        app.get('/user', function (req, res) {
-          res.end('tj');
-        });
+        app.get('/user', (req, res) => {
+          res.end('tj')
+        })
 
         request(app)
           .get('/user/')
-          .expect(404, done);
+          .expect(404, done)
       })
     })
   })
 
-  it('should allow literal "."', function (done) {
-    var app = express();
+  it('should allow literal "."', (done) => {
+    const app = express()
 
-    app.get('/api/users/:from..:to', function (req, res) {
-      var from = req.params.from
-        , to = req.params.to;
+    app.get('/api/users/:from..:to', (req, res) => {
+      const from = req.params.from
+      const to = req.params.to
 
-      res.end('users from ' + from + ' to ' + to);
-    });
+      res.end('users from ' + from + ' to ' + to)
+    })
 
     request(app)
       .get('/api/users/1..50')
-      .expect('users from 1 to 50', done);
+      .expect('users from 1 to 50', done)
   })
 
-  describe(':name', function () {
-    it('should denote a capture group', function (done) {
-      var app = express();
+  describe(':name', () => {
+    it('should denote a capture group', (done) => {
+      const app = express()
 
-      app.get('/user/:user', function (req, res) {
-        res.end(req.params.user);
-      });
+      app.get('/user/:user', (req, res) => {
+        res.end(req.params.user)
+      })
 
       request(app)
         .get('/user/tj')
-        .expect('tj', done);
+        .expect('tj', done)
     })
 
-    it('should match a single segment only', function (done) {
-      var app = express();
+    it('should match a single segment only', (done) => {
+      const app = express()
 
-      app.get('/user/:user', function (req, res) {
-        res.end(req.params.user);
-      });
+      app.get('/user/:user', (req, res) => {
+        res.end(req.params.user)
+      })
 
       request(app)
         .get('/user/tj/edit')
-        .expect(404, done);
+        .expect(404, done)
     })
 
-    it('should allow several capture groups', function (done) {
-      var app = express();
+    it('should allow several capture groups', (done) => {
+      const app = express()
 
-      app.get('/user/:user/:op', function (req, res) {
-        res.end(req.params.op + 'ing ' + req.params.user);
-      });
+      app.get('/user/:user/:op', (req, res) => {
+        res.end(req.params.op + 'ing ' + req.params.user)
+      })
 
       request(app)
         .get('/user/tj/edit')
-        .expect('editing tj', done);
+        .expect('editing tj', done)
     })
 
-    it('should work following a partial capture group', function (done) {
-      var app = express();
-      var cb = after(2, done);
+    it('should work following a partial capture group', (done) => {
+      const app = express()
+      const cb = after(2, done)
 
-      app.get('/user{s}/:user/:op', function (req, res) {
-        res.end(req.params.op + 'ing ' + req.params.user + (req.url.startsWith('/users') ? ' (old)' : ''));
-      });
+      app.get('/user{s}/:user/:op', (req, res) => {
+        res.end(req.params.op + 'ing ' + req.params.user + (req.url.startsWith('/users') ? ' (old)' : ''))
+      })
 
       request(app)
         .get('/user/tj/edit')
-        .expect('editing tj', cb);
+        .expect('editing tj', cb)
 
       request(app)
         .get('/users/tj/edit')
-        .expect('editing tj (old)', cb);
+        .expect('editing tj (old)', cb)
     })
 
-    it('should work inside literal parenthesis', function (done) {
-      var app = express();
+    it('should work inside literal parenthesis', (done) => {
+      const app = express()
 
-      app.get('/:user\\(:op\\)', function (req, res) {
-        res.end(req.params.op + 'ing ' + req.params.user);
-      });
+      app.get('/:user\\(:op\\)', (req, res) => {
+        res.end(req.params.op + 'ing ' + req.params.user)
+      })
 
       request(app)
         .get('/tj(edit)')
-        .expect('editing tj', done);
+        .expect('editing tj', done)
     })
 
-    it('should work in array of paths', function (done) {
-      var app = express();
-      var cb = after(2, done);
+    it('should work in array of paths', (done) => {
+      const app = express()
+      const cb = after(2, done)
 
-      app.get(['/user/:user/poke', '/user/:user/pokes'], function (req, res) {
-        res.end('poking ' + req.params.user);
-      });
+      app.get(['/user/:user/poke', '/user/:user/pokes'], (req, res) => {
+        res.end('poking ' + req.params.user)
+      })
 
       request(app)
         .get('/user/tj/poke')
-        .expect('poking tj', cb);
+        .expect('poking tj', cb)
 
       request(app)
         .get('/user/tj/pokes')
-        .expect('poking tj', cb);
+        .expect('poking tj', cb)
     })
   })
 
-  describe(':name?', function () {
-    it('should denote an optional capture group', function (done) {
-      var app = express();
+  describe(':name?', () => {
+    it('should denote an optional capture group', (done) => {
+      const app = express()
 
-      app.get('/user/:user{/:op}', function (req, res) {
-        var op = req.params.op || 'view';
-        res.end(op + 'ing ' + req.params.user);
-      });
+      app.get('/user/:user{/:op}', (req, res) => {
+        const op = req.params.op || 'view'
+        res.end(op + 'ing ' + req.params.user)
+      })
 
       request(app)
         .get('/user/tj')
-        .expect('viewing tj', done);
+        .expect('viewing tj', done)
     })
 
-    it('should populate the capture group', function (done) {
-      var app = express();
+    it('should populate the capture group', (done) => {
+      const app = express()
 
-      app.get('/user/:user{/:op}', function (req, res) {
-        var op = req.params.op || 'view';
-        res.end(op + 'ing ' + req.params.user);
-      });
+      app.get('/user/:user{/:op}', (req, res) => {
+        const op = req.params.op || 'view'
+        res.end(op + 'ing ' + req.params.user)
+      })
 
       request(app)
         .get('/user/tj/edit')
-        .expect('editing tj', done);
+        .expect('editing tj', done)
     })
   })
 
-  describe(':name*', function () {
-    it('should match one segment', function (done) {
-      var app = express()
+  describe(':name*', () => {
+    it('should match one segment', (done) => {
+      const app = express()
 
-      app.get('/user/*user', function (req, res) {
+      app.get('/user/*user', (req, res) => {
         res.end(req.params.user[0])
       })
 
@@ -714,10 +714,10 @@ describe('app.router', function () {
         .expect('122', done)
     })
 
-    it('should match many segments', function (done) {
-      var app = express()
+    it('should match many segments', (done) => {
+      const app = express()
 
-      app.get('/user/*user', function (req, res) {
+      app.get('/user/*user', (req, res) => {
         res.end(req.params.user.join('/'))
       })
 
@@ -726,10 +726,10 @@ describe('app.router', function () {
         .expect('1/2/3/4', done)
     })
 
-    it('should match zero segments', function (done) {
-      var app = express()
+    it('should match zero segments', (done) => {
+      const app = express()
 
-      app.get('/user{/*user}', function (req, res) {
+      app.get('/user{/*user}', (req, res) => {
         res.end(req.params.user)
       })
 
@@ -739,11 +739,11 @@ describe('app.router', function () {
     })
   })
 
-  describe(':name+', function () {
-    it('should match one segment', function (done) {
-      var app = express()
+  describe(':name+', () => {
+    it('should match one segment', (done) => {
+      const app = express()
 
-      app.get('/user/*user', function (req, res) {
+      app.get('/user/*user', (req, res) => {
         res.end(req.params.user[0])
       })
 
@@ -752,10 +752,10 @@ describe('app.router', function () {
         .expect(200, '122', done)
     })
 
-    it('should match many segments', function (done) {
-      var app = express()
+    it('should match many segments', (done) => {
+      const app = express()
 
-      app.get('/user/*user', function (req, res) {
+      app.get('/user/*user', (req, res) => {
         res.end(req.params.user.join('/'))
       })
 
@@ -764,10 +764,10 @@ describe('app.router', function () {
         .expect(200, '1/2/3/4', done)
     })
 
-    it('should not match zero segments', function (done) {
-      var app = express()
+    it('should not match zero segments', (done) => {
+      const app = express()
 
-      app.get('/user/*user', function (req, res) {
+      app.get('/user/*user', (req, res) => {
         res.end(req.params.user)
       })
 
@@ -777,14 +777,14 @@ describe('app.router', function () {
     })
   })
 
-  describe('.:name', function () {
-    it('should denote a format', function (done) {
-      var app = express();
-      var cb = after(2, done)
+  describe('.:name', () => {
+    it('should denote a format', (done) => {
+      const app = express()
+      const cb = after(2, done)
 
-      app.get('/:name.:format', function (req, res) {
-        res.end(req.params.name + ' as ' + req.params.format);
-      });
+      app.get('/:name.:format', (req, res) => {
+        res.end(req.params.name + ' as ' + req.params.format)
+      })
 
       request(app)
         .get('/foo.json')
@@ -796,14 +796,14 @@ describe('app.router', function () {
     })
   })
 
-  describe('.:name?', function () {
-    it('should denote an optional format', function (done) {
-      var app = express();
-      var cb = after(2, done)
+  describe('.:name?', () => {
+    it('should denote an optional format', (done) => {
+      const app = express()
+      const cb = after(2, done)
 
-      app.get('/:name{.:format}', function (req, res) {
-        res.end(req.params.name + ' as ' + (req.params.format || 'html'));
-      });
+      app.get('/:name{.:format}', (req, res) => {
+        res.end(req.params.name + ' as ' + (req.params.format || 'html'))
+      })
 
       request(app)
         .get('/foo')
@@ -815,29 +815,29 @@ describe('app.router', function () {
     })
   })
 
-  describe('when next() is called', function () {
-    it('should continue lookup', function (done) {
-      var app = express()
-        , calls = [];
+  describe('when next() is called', () => {
+    it('should continue lookup', (done) => {
+      const app = express()
+      const calls = []
 
-      app.get('/foo{/:bar}', function (req, res, next) {
-        calls.push('/foo/:bar?');
-        next();
-      });
+      app.get('/foo{/:bar}', (req, res, next) => {
+        calls.push('/foo/:bar?')
+        next()
+      })
 
-      app.get('/bar', function () {
-        assert(0);
-      });
+      app.get('/bar', () => {
+        assert(0)
+      })
 
-      app.get('/foo', function (req, res, next) {
-        calls.push('/foo');
-        next();
-      });
+      app.get('/foo', (req, res, next) => {
+        calls.push('/foo')
+        next()
+      })
 
-      app.get('/foo', function (req, res) {
-        calls.push('/foo 2');
+      app.get('/foo', (req, res) => {
+        calls.push('/foo 2')
         res.json(calls)
-      });
+      })
 
       request(app)
         .get('/foo')
@@ -845,20 +845,20 @@ describe('app.router', function () {
     })
   })
 
-  describe('when next("route") is called', function () {
-    it('should jump to next route', function (done) {
-      var app = express()
+  describe('when next("route") is called', () => {
+    it('should jump to next route', (done) => {
+      const app = express()
 
-      function fn(req, res, next) {
+      function fn (req, res, next) {
         res.set('X-Hit', '1')
         next('route')
       }
 
-      app.get('/foo', fn, function (req, res) {
+      app.get('/foo', fn, (req, res) => {
         res.end('failure')
-      });
+      })
 
-      app.get('/foo', function (req, res) {
+      app.get('/foo', (req, res) => {
         res.end('success')
       })
 
@@ -869,27 +869,27 @@ describe('app.router', function () {
     })
   })
 
-  describe('when next("router") is called', function () {
-    it('should jump out of router', function (done) {
-      var app = express()
-      var router = express.Router()
+  describe('when next("router") is called', () => {
+    it('should jump out of router', (done) => {
+      const app = express()
+      const router = express.Router()
 
-      function fn(req, res, next) {
+      function fn (req, res, next) {
         res.set('X-Hit', '1')
         next('router')
       }
 
-      router.get('/foo', fn, function (req, res) {
+      router.get('/foo', fn, (req, res) => {
         res.end('failure')
       })
 
-      router.get('/foo', function (req, res) {
+      router.get('/foo', (req, res) => {
         res.end('failure')
       })
 
       app.use(router)
 
-      app.get('/foo', function (req, res) {
+      app.get('/foo', (req, res) => {
         res.end('success')
       })
 
@@ -900,32 +900,32 @@ describe('app.router', function () {
     })
   })
 
-  describe('when next(err) is called', function () {
-    it('should break out of app.router', function (done) {
-      var app = express()
-        , calls = [];
+  describe('when next(err) is called', () => {
+    it('should break out of app.router', (done) => {
+      const app = express()
+      const calls = []
 
-      app.get('/foo{/:bar}', function (req, res, next) {
-        calls.push('/foo/:bar?');
-        next();
-      });
+      app.get('/foo{/:bar}', (req, res, next) => {
+        calls.push('/foo/:bar?')
+        next()
+      })
 
-      app.get('/bar', function () {
-        assert(0);
-      });
+      app.get('/bar', () => {
+        assert(0)
+      })
 
-      app.get('/foo', function (req, res, next) {
-        calls.push('/foo');
-        next(new Error('fail'));
-      });
+      app.get('/foo', (req, res, next) => {
+        calls.push('/foo')
+        next(new Error('fail'))
+      })
 
-      app.get('/foo', function () {
-        assert(0);
-      });
+      app.get('/foo', () => {
+        assert(0)
+      })
 
-      app.use(function (err, req, res, next) {
+      app.use((err, req, res, next) => {
         res.json({
-          calls: calls,
+          calls,
           error: err.message
         })
       })
@@ -935,25 +935,25 @@ describe('app.router', function () {
         .expect(200, { calls: ['/foo/:bar?', '/foo'], error: 'fail' }, done)
     })
 
-    it('should call handler in same route, if exists', function (done) {
-      var app = express();
+    it('should call handler in same route, if exists', (done) => {
+      const app = express()
 
-      function fn1(req, res, next) {
-        next(new Error('boom!'));
+      function fn1 (req, res, next) {
+        next(new Error('boom!'))
       }
 
-      function fn2(req, res, next) {
-        res.send('foo here');
+      function fn2 (req, res, next) {
+        res.send('foo here')
       }
 
-      function fn3(err, req, res, next) {
-        res.send('route go ' + err.message);
+      function fn3 (err, req, res, next) {
+        res.send('route go ' + err.message)
       }
 
-      app.get('/foo', fn1, fn2, fn3);
+      app.get('/foo', fn1, fn2, fn3)
 
-      app.use(function (err, req, res, next) {
-        res.end('error!');
+      app.use((err, req, res, next) => {
+        res.end('error!')
       })
 
       request(app)
@@ -962,16 +962,14 @@ describe('app.router', function () {
     })
   })
 
-  describe('promise support', function () {
-    it('should pass rejected promise value', function (done) {
-      var app = express()
-      var router = new express.Router()
+  describe('promise support', () => {
+    it('should pass rejected promise value', (done) => {
+      const app = express()
+      const router = new express.Router()
 
-      router.use(function createError(req, res, next) {
-        return Promise.reject(new Error('boom!'))
-      })
+      router.use((req, res, next) => Promise.reject(new Error('boom!')))
 
-      router.use(function sawError(err, req, res, next) {
+      router.use((err, req, res, next) => {
         res.send('saw ' + err.name + ': ' + err.message)
       })
 
@@ -982,15 +980,16 @@ describe('app.router', function () {
         .expect(200, 'saw Error: boom!', done)
     })
 
-    it('should pass rejected promise without value', function (done) {
-      var app = express()
-      var router = new express.Router()
+    it('should pass rejected promise without value', (done) => {
+      const app = express()
+      const router = new express.Router()
 
-      router.use(function createError(req, res, next) {
-        return Promise.reject()
-      })
+      router.use((req, res, next) =>
+        // eslint-disable-next-line prefer-promise-reject-errors
+        Promise.reject()
+      )
 
-      router.use(function sawError(err, req, res, next) {
+      router.use((err, req, res, next) => {
         res.send('saw ' + err.name + ': ' + err.message)
       })
 
@@ -1001,16 +1000,16 @@ describe('app.router', function () {
         .expect(200, 'saw Error: Rejected promise', done)
     })
 
-    it('should ignore resolved promise', function (done) {
-      var app = express()
-      var router = new express.Router()
+    it('should ignore resolved promise', (done) => {
+      const app = express()
+      const router = new express.Router()
 
-      router.use(function createError(req, res, next) {
+      router.use((req, res, next) => {
         res.send('saw GET /foo')
         return Promise.resolve('foo')
       })
 
-      router.use(function () {
+      router.use(() => {
         done(new Error('Unexpected middleware invoke'))
       })
 
@@ -1021,20 +1020,16 @@ describe('app.router', function () {
         .expect(200, 'saw GET /foo', done)
     })
 
-    describe('error handling', function () {
-      it('should pass rejected promise value', function (done) {
-        var app = express()
-        var router = new express.Router()
+    describe('error handling', () => {
+      it('should pass rejected promise value', (done) => {
+        const app = express()
+        const router = new express.Router()
 
-        router.use(function createError(req, res, next) {
-          return Promise.reject(new Error('boom!'))
-        })
+        router.use((req, res, next) => Promise.reject(new Error('boom!')))
 
-        router.use(function handleError(err, req, res, next) {
-          return Promise.reject(new Error('caught: ' + err.message))
-        })
+        router.use((err, req, res, next) => Promise.reject(new Error('caught: ' + err.message)))
 
-        router.use(function sawError(err, req, res, next) {
+        router.use((err, req, res, next) => {
           res.send('saw ' + err.name + ': ' + err.message)
         })
 
@@ -1045,19 +1040,18 @@ describe('app.router', function () {
           .expect(200, 'saw Error: caught: boom!', done)
       })
 
-      it('should pass rejected promise without value', function (done) {
-        var app = express()
-        var router = new express.Router()
+      it('should pass rejected promise without value', (done) => {
+        const app = express()
+        const router = new express.Router()
 
-        router.use(function createError(req, res, next) {
-          return Promise.reject()
-        })
+        router.use((req, res, next) =>
+          // eslint-disable-next-line prefer-promise-reject-errors
+          Promise.reject()
+        )
 
-        router.use(function handleError(err, req, res, next) {
-          return Promise.reject(new Error('caught: ' + err.message))
-        })
+        router.use((err, req, res, next) => Promise.reject(new Error('caught: ' + err.message)))
 
-        router.use(function sawError(err, req, res, next) {
+        router.use((err, req, res, next) => {
           res.send('saw ' + err.name + ': ' + err.message)
         })
 
@@ -1068,20 +1062,18 @@ describe('app.router', function () {
           .expect(200, 'saw Error: caught: Rejected promise', done)
       })
 
-      it('should ignore resolved promise', function (done) {
-        var app = express()
-        var router = new express.Router()
+      it('should ignore resolved promise', (done) => {
+        const app = express()
+        const router = new express.Router()
 
-        router.use(function createError(req, res, next) {
-          return Promise.reject(new Error('boom!'))
-        })
+        router.use((req, res, next) => Promise.reject(new Error('boom!')))
 
-        router.use(function handleError(err, req, res, next) {
+        router.use((err, req, res, next) => {
           res.send('saw ' + err.name + ': ' + err.message)
           return Promise.resolve('foo')
         })
 
-        router.use(function () {
+        router.use(() => {
           done(new Error('Unexpected middleware invoke'))
         })
 
@@ -1094,122 +1086,121 @@ describe('app.router', function () {
     })
   })
 
-  it('should allow rewriting of the url', function (done) {
-    var app = express();
+  it('should allow rewriting of the url', (done) => {
+    const app = express()
 
-    app.get('/account/edit', function (req, res, next) {
-      req.user = { id: 12 }; // faux authenticated user
-      req.url = '/user/' + req.user.id + '/edit';
-      next();
-    });
+    app.get('/account/edit', (req, res, next) => {
+      req.user = { id: 12 } // faux authenticated user
+      req.url = '/user/' + req.user.id + '/edit'
+      next()
+    })
 
-    app.get('/user/:id/edit', function (req, res) {
-      res.send('editing user ' + req.params.id);
-    });
+    app.get('/user/:id/edit', (req, res) => {
+      res.send('editing user ' + req.params.id)
+    })
 
     request(app)
       .get('/account/edit')
-      .expect('editing user 12', done);
+      .expect('editing user 12', done)
   })
 
-  it('should run in order added', function (done) {
-    var app = express();
-    var path = [];
-
-    app.get('/*path', function (req, res, next) {
-      path.push(0);
-      next();
-    });
-
-    app.get('/user/:id', function (req, res, next) {
-      path.push(1);
-      next();
-    });
-
-    app.use(function (req, res, next) {
-      path.push(2);
-      next();
-    });
-
-    app.all('/user/:id', function (req, res, next) {
-      path.push(3);
-      next();
-    });
-
-    app.get('/*splat', function (req, res, next) {
-      path.push(4);
-      next();
-    });
-
-    app.use(function (req, res, next) {
-      path.push(5);
+  it('should run in order added', (done) => {
+    const app = express()
+    const path = []
+
+    app.get('/*path', (req, res, next) => {
+      path.push(0)
+      next()
+    })
+
+    app.get('/user/:id', (req, res, next) => {
+      path.push(1)
+      next()
+    })
+
+    app.use((req, res, next) => {
+      path.push(2)
+      next()
+    })
+
+    app.all('/user/:id', (req, res, next) => {
+      path.push(3)
+      next()
+    })
+
+    app.get('/*splat', (req, res, next) => {
+      path.push(4)
+      next()
+    })
+
+    app.use((req, res, next) => {
+      path.push(5)
       res.end(path.join(','))
-    });
+    })
 
     request(app)
       .get('/user/1')
-      .expect(200, '0,1,2,3,4,5', done);
+      .expect(200, '0,1,2,3,4,5', done)
   })
 
-  it('should be chainable', function () {
-    var app = express();
-    assert.strictEqual(app.get('/', function () { }), app)
+  it('should be chainable', () => {
+    const app = express()
+    assert.strictEqual(app.get('/', () => { }), app)
   })
 
-  it('should not use disposed router/middleware', function (done) {
+  it('should not use disposed router/middleware', (done) => {
     // more context: https://github.com/expressjs/express/issues/5743#issuecomment-2277148412
 
-    var app = express();
-    var router = new express.Router();
+    const app = express()
+    let router = new express.Router()
 
-    router.use(function (req, res, next) {
-      res.setHeader('old', 'foo');
-      next();
-    });
+    router.use((req, res, next) => {
+      res.setHeader('old', 'foo')
+      next()
+    })
 
-    app.use(function (req, res, next) {
-      return router.handle(req, res, next);
-    });
+    app.use((req, res, next) => router.handle(req, res, next))
 
-    app.get('/', function (req, res, next) {
-      res.send('yee');
-      next();
-    });
+    app.get('/', (req, res, next) => {
+      res.send('yee')
+      next()
+    })
 
     request(app)
       .get('/')
       .expect('old', 'foo')
-      .expect(function (res) {
+      .expect((res) => {
         if (typeof res.headers['new'] !== 'undefined') {
-          throw new Error('`new` header should not be present');
+          throw new Error('`new` header should not be present')
         }
       })
-      .expect(200, 'yee', function (err, res) {
-        if (err) return done(err);
+      .expect(200, 'yee', (err, res) => {
+        if (err) return done(err)
 
-        router = new express.Router();
+        router = new express.Router()
 
-        router.use(function (req, res, next) {
-          res.setHeader('new', 'bar');
-          next();
-        });
+        router.use((req, res, next) => {
+          res.setHeader('new', 'bar')
+          next()
+        })
 
         request(app)
           .get('/')
           .expect('new', 'bar')
-          .expect(function (res) {
+          .expect((res) => {
             if (typeof res.headers['old'] !== 'undefined') {
-              throw new Error('`old` header should not be present');
+              throw new Error('`old` header should not be present')
             }
           })
-          .expect(200, 'yee', done);
-      });
+          .expect(200, 'yee', done)
+      })
   })
 })
 
-function supportsRegexp(source) {
+function supportsRegexp (source) {
   try {
-    new RegExp(source)
+    // eslint-disable-next-line no-unused-vars
+    const _ = new RegExp(source)
     return true
   } catch (e) {
     return false
diff --git a/test/app.routes.error.js b/test/app.routes.error.js
index ed53c7857ba..3b90cea2bf5 100644
--- a/test/app.routes.error.js
+++ b/test/app.routes.error.js
@@ -1,62 +1,62 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('../')
-  , request = require('supertest');
+const assert = require('node:assert')
+const express = require('../')
+const request = require('supertest')
 
-describe('app', function(){
-  describe('.VERB()', function(){
-    it('should not get invoked without error handler on error', function(done) {
-      var app = express();
+describe('app', () => {
+  describe('.VERB()', () => {
+    it('should not get invoked without error handler on error', (done) => {
+      const app = express()
 
-      app.use(function(req, res, next){
+      app.use((req, res, next) => {
         next(new Error('boom!'))
-      });
+      })
 
-      app.get('/bar', function(req, res){
-        res.send('hello, world!');
-      });
+      app.get('/bar', (req, res) => {
+        res.send('hello, world!')
+      })
 
       request(app)
-      .post('/bar')
-      .expect(500, /Error: boom!/, done);
-    });
-
-    it('should only call an error handling routing callback when an error is propagated', function(done){
-      var app = express();
-
-      var a = false;
-      var b = false;
-      var c = false;
-      var d = false;
-
-      app.get('/', function(req, res, next){
-        next(new Error('fabricated error'));
-      }, function(req, res, next) {
-        a = true;
-        next();
-      }, function(err, req, res, next){
-        b = true;
+        .post('/bar')
+        .expect(500, /Error: boom!/, done)
+    })
+
+    it('should only call an error handling routing callback when an error is propagated', (done) => {
+      const app = express()
+
+      let a = false
+      let b = false
+      let c = false
+      let d = false
+
+      app.get('/', (req, res, next) => {
+        next(new Error('fabricated error'))
+      }, (req, res, next) => {
+        a = true
+        next()
+      }, (err, req, res, next) => {
+        b = true
         assert.strictEqual(err.message, 'fabricated error')
-        next(err);
-      }, function(err, req, res, next){
-        c = true;
+        next(err)
+      }, (err, req, res, next) => {
+        c = true
         assert.strictEqual(err.message, 'fabricated error')
-        next();
-      }, function(err, req, res, next){
-        d = true;
-        next();
-      }, function(req, res){
+        next()
+      }, (err, req, res, next) => {
+        d = true
+        next()
+      }, (req, res) => {
         assert.ok(!a)
         assert.ok(b)
         assert.ok(c)
         assert.ok(!d)
-        res.sendStatus(204);
-      });
+        res.sendStatus(204)
+      })
 
       request(app)
-      .get('/')
-      .expect(204, done);
+        .get('/')
+        .expect(204, done)
     })
   })
 })
diff --git a/test/app.use.js b/test/app.use.js
index 1d56aa3b029..8af7052ae5a 100644
--- a/test/app.use.js
+++ b/test/app.use.js
@@ -1,55 +1,55 @@
 'use strict'
 
-var after = require('after');
-var assert = require('node:assert')
-var express = require('..');
-var request = require('supertest');
+const after = require('after')
+const assert = require('node:assert')
+const express = require('../')
+const request = require('supertest')
 
-describe('app', function(){
-  it('should emit "mount" when mounted', function(done){
-    var blog = express()
-      , app = express();
+describe('app', () => {
+  it('should emit "mount" when mounted', (done) => {
+    const blog = express()
+    const app = express()
 
-    blog.on('mount', function(arg){
+    blog.on('mount', (arg) => {
       assert.strictEqual(arg, app)
-      done();
-    });
+      done()
+    })
 
-    app.use(blog);
+    app.use(blog)
   })
 
-  describe('.use(app)', function(){
-    it('should mount the app', function(done){
-      var blog = express()
-        , app = express();
+  describe('.use(app)', () => {
+    it('should mount the app', (done) => {
+      const blog = express()
+      const app = express()
 
-      blog.get('/blog', function(req, res){
-        res.end('blog');
-      });
+      blog.get('/blog', (req, res) => {
+        res.end('blog')
+      })
 
-      app.use(blog);
+      app.use(blog)
 
       request(app)
-      .get('/blog')
-      .expect('blog', done);
+        .get('/blog')
+        .expect('blog', done)
     })
 
-    it('should support mount-points', function(done){
-      var blog = express()
-        , forum = express()
-        , app = express();
-      var cb = after(2, done)
+    it('should support mount-points', (done) => {
+      const blog = express()
+      const forum = express()
+      const app = express()
+      const cb = after(2, done)
 
-      blog.get('/', function(req, res){
-        res.end('blog');
-      });
+      blog.get('/', (req, res) => {
+        res.end('blog')
+      })
 
-      forum.get('/', function(req, res){
-        res.end('forum');
-      });
+      forum.get('/', (req, res) => {
+        res.end('forum')
+      })
 
-      app.use('/blog', blog);
-      app.use('/forum', forum);
+      app.use('/blog', blog)
+      app.use('/forum', forum)
 
       request(app)
         .get('/blog')
@@ -60,483 +60,483 @@ describe('app', function(){
         .expect(200, 'forum', cb)
     })
 
-    it('should set the child\'s .parent', function(){
-      var blog = express()
-        , app = express();
+    it('should set the child\'s .parent', () => {
+      const blog = express()
+      const app = express()
 
-      app.use('/blog', blog);
+      app.use('/blog', blog)
       assert.strictEqual(blog.parent, app)
     })
 
-    it('should support dynamic routes', function(done){
-      var blog = express()
-        , app = express();
+    it('should support dynamic routes', (done) => {
+      const blog = express()
+      const app = express()
 
-      blog.get('/', function(req, res){
-        res.end('success');
-      });
+      blog.get('/', (req, res) => {
+        res.end('success')
+      })
 
-      app.use('/post/:article', blog);
+      app.use('/post/:article', blog)
 
       request(app)
-      .get('/post/once-upon-a-time')
-      .expect('success', done);
+        .get('/post/once-upon-a-time')
+        .expect('success', done)
     })
 
-    it('should support mounted app anywhere', function(done){
-      var cb = after(3, done);
-      var blog = express()
-        , other = express()
-        , app = express();
+    it('should support mounted app anywhere', (done) => {
+      const cb = after(3, done)
+      const blog = express()
+      const other = express()
+      const app = express()
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      blog.get('/', function(req, res){
-        res.end('success');
-      });
+      blog.get('/', (req, res) => {
+        res.end('success')
+      })
 
-      blog.once('mount', function (parent) {
+      blog.once('mount', (parent) => {
         assert.strictEqual(parent, app)
-        cb();
-      });
-      other.once('mount', function (parent) {
+        cb()
+      })
+      other.once('mount', (parent) => {
         assert.strictEqual(parent, app)
-        cb();
-      });
+        cb()
+      })
 
-      app.use('/post/:article', fn1, other, fn2, blog);
+      app.use('/post/:article', fn1, other, fn2, blog)
 
       request(app)
-      .get('/post/once-upon-a-time')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('success', cb);
+        .get('/post/once-upon-a-time')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('success', cb)
     })
   })
 
-  describe('.use(middleware)', function(){
-    it('should accept multiple arguments', function (done) {
-      var app = express();
+  describe('.use(middleware)', () => {
+    it('should accept multiple arguments', (done) => {
+      const app = express()
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      app.use(fn1, fn2, function fn3(req, res) {
-        res.setHeader('x-fn-3', 'hit');
-        res.end();
-      });
+      app.use(fn1, fn2, (req, res) => {
+        res.setHeader('x-fn-3', 'hit')
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, done);
+        .get('/')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, done)
     })
 
-    it('should invoke middleware for all requests', function (done) {
-      var app = express();
-      var cb = after(3, done);
+    it('should invoke middleware for all requests', (done) => {
+      const app = express()
+      const cb = after(3, done)
 
-      app.use(function (req, res) {
-        res.send('saw ' + req.method + ' ' + req.url);
-      });
+      app.use((req, res) => {
+        res.send('saw ' + req.method + ' ' + req.url)
+      })
 
       request(app)
-      .get('/')
-      .expect(200, 'saw GET /', cb);
+        .get('/')
+        .expect(200, 'saw GET /', cb)
 
       request(app)
-      .options('/')
-      .expect(200, 'saw OPTIONS /', cb);
+        .options('/')
+        .expect(200, 'saw OPTIONS /', cb)
 
       request(app)
-      .post('/foo')
-      .expect(200, 'saw POST /foo', cb);
+        .post('/foo')
+        .expect(200, 'saw POST /foo', cb)
     })
 
-    it('should accept array of middleware', function (done) {
-      var app = express();
+    it('should accept array of middleware', (done) => {
+      const app = express()
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      function fn3(req, res, next) {
-        res.setHeader('x-fn-3', 'hit');
-        res.end();
+      function fn3 (req, res, next) {
+        res.setHeader('x-fn-3', 'hit')
+        res.end()
       }
 
-      app.use([fn1, fn2, fn3]);
+      app.use([fn1, fn2, fn3])
 
       request(app)
-      .get('/')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, done);
+        .get('/')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, done)
     })
 
-    it('should accept multiple arrays of middleware', function (done) {
-      var app = express();
+    it('should accept multiple arrays of middleware', (done) => {
+      const app = express()
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      function fn3(req, res, next) {
-        res.setHeader('x-fn-3', 'hit');
-        res.end();
+      function fn3 (req, res, next) {
+        res.setHeader('x-fn-3', 'hit')
+        res.end()
       }
 
-      app.use([fn1, fn2], [fn3]);
+      app.use([fn1, fn2], [fn3])
 
       request(app)
-      .get('/')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, done);
+        .get('/')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, done)
     })
 
-    it('should accept nested arrays of middleware', function (done) {
-      var app = express();
+    it('should accept nested arrays of middleware', (done) => {
+      const app = express()
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      function fn3(req, res, next) {
-        res.setHeader('x-fn-3', 'hit');
-        res.end();
+      function fn3 (req, res, next) {
+        res.setHeader('x-fn-3', 'hit')
+        res.end()
       }
 
-      app.use([[fn1], fn2], [fn3]);
+      app.use([[fn1], fn2], [fn3])
 
       request(app)
-      .get('/')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, done);
+        .get('/')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, done)
     })
   })
 
-  describe('.use(path, middleware)', function(){
-    it('should require middleware', function () {
-      var app = express()
-      assert.throws(function () { app.use('/') }, 'TypeError: app.use() requires a middleware function')
+  describe('.use(path, middleware)', () => {
+    it('should require middleware', () => {
+      const app = express()
+      assert.throws(() => { app.use('/') }, 'TypeError: app.use() requires a middleware function')
     })
 
-    it('should reject string as middleware', function () {
-      var app = express()
-      assert.throws(function () { app.use('/', 'foo') }, /argument handler must be a function/)
+    it('should reject string as middleware', () => {
+      const app = express()
+      assert.throws(() => { app.use('/', 'foo') }, /argument handler must be a function/)
     })
 
-    it('should reject number as middleware', function () {
-      var app = express()
-      assert.throws(function () { app.use('/', 42) }, /argument handler must be a function/)
+    it('should reject number as middleware', () => {
+      const app = express()
+      assert.throws(() => { app.use('/', 42) }, /argument handler must be a function/)
     })
 
-    it('should reject null as middleware', function () {
-      var app = express()
-      assert.throws(function () { app.use('/', null) }, /argument handler must be a function/)
+    it('should reject null as middleware', () => {
+      const app = express()
+      assert.throws(() => { app.use('/', null) }, /argument handler must be a function/)
     })
 
-    it('should reject Date as middleware', function () {
-      var app = express()
-      assert.throws(function () { app.use('/', new Date()) }, /argument handler must be a function/)
+    it('should reject Date as middleware', () => {
+      const app = express()
+      assert.throws(() => { app.use('/', new Date()) }, /argument handler must be a function/)
     })
 
-    it('should strip path from req.url', function (done) {
-      var app = express();
+    it('should strip path from req.url', (done) => {
+      const app = express()
 
-      app.use('/foo', function (req, res) {
-        res.send('saw ' + req.method + ' ' + req.url);
-      });
+      app.use('/foo', (req, res) => {
+        res.send('saw ' + req.method + ' ' + req.url)
+      })
 
       request(app)
-      .get('/foo/bar')
-      .expect(200, 'saw GET /bar', done);
+        .get('/foo/bar')
+        .expect(200, 'saw GET /bar', done)
     })
 
-    it('should accept multiple arguments', function (done) {
-      var app = express();
+    it('should accept multiple arguments', (done) => {
+      const app = express()
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      app.use('/foo', fn1, fn2, function fn3(req, res) {
-        res.setHeader('x-fn-3', 'hit');
-        res.end();
-      });
+      app.use('/foo', fn1, fn2, (req, res) => {
+        res.setHeader('x-fn-3', 'hit')
+        res.end()
+      })
 
       request(app)
-      .get('/foo')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, done);
+        .get('/foo')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, done)
     })
 
-    it('should invoke middleware for all requests starting with path', function (done) {
-      var app = express();
-      var cb = after(3, done);
+    it('should invoke middleware for all requests starting with path', (done) => {
+      const app = express()
+      const cb = after(3, done)
 
-      app.use('/foo', function (req, res) {
-        res.send('saw ' + req.method + ' ' + req.url);
-      });
+      app.use('/foo', (req, res) => {
+        res.send('saw ' + req.method + ' ' + req.url)
+      })
 
       request(app)
-      .get('/')
-      .expect(404, cb);
+        .get('/')
+        .expect(404, cb)
 
       request(app)
-      .post('/foo')
-      .expect(200, 'saw POST /', cb);
+        .post('/foo')
+        .expect(200, 'saw POST /', cb)
 
       request(app)
-      .post('/foo/bar')
-      .expect(200, 'saw POST /bar', cb);
+        .post('/foo/bar')
+        .expect(200, 'saw POST /bar', cb)
     })
 
-    it('should work if path has trailing slash', function (done) {
-      var app = express();
-      var cb = after(3, done);
+    it('should work if path has trailing slash', (done) => {
+      const app = express()
+      const cb = after(3, done)
 
-      app.use('/foo/', function (req, res) {
-        res.send('saw ' + req.method + ' ' + req.url);
-      });
+      app.use('/foo/', (req, res) => {
+        res.send('saw ' + req.method + ' ' + req.url)
+      })
 
       request(app)
-      .get('/')
-      .expect(404, cb);
+        .get('/')
+        .expect(404, cb)
 
       request(app)
-      .post('/foo')
-      .expect(200, 'saw POST /', cb);
+        .post('/foo')
+        .expect(200, 'saw POST /', cb)
 
       request(app)
-      .post('/foo/bar')
-      .expect(200, 'saw POST /bar', cb);
+        .post('/foo/bar')
+        .expect(200, 'saw POST /bar', cb)
     })
 
-    it('should accept array of middleware', function (done) {
-      var app = express();
+    it('should accept array of middleware', (done) => {
+      const app = express()
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      function fn3(req, res, next) {
-        res.setHeader('x-fn-3', 'hit');
-        res.end();
+      function fn3 (req, res, next) {
+        res.setHeader('x-fn-3', 'hit')
+        res.end()
       }
 
-      app.use('/foo', [fn1, fn2, fn3]);
+      app.use('/foo', [fn1, fn2, fn3])
 
       request(app)
-      .get('/foo')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, done);
+        .get('/foo')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, done)
     })
 
-    it('should accept multiple arrays of middleware', function (done) {
-      var app = express();
+    it('should accept multiple arrays of middleware', (done) => {
+      const app = express()
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      function fn3(req, res, next) {
-        res.setHeader('x-fn-3', 'hit');
-        res.end();
+      function fn3 (req, res, next) {
+        res.setHeader('x-fn-3', 'hit')
+        res.end()
       }
 
-      app.use('/foo', [fn1, fn2], [fn3]);
+      app.use('/foo', [fn1, fn2], [fn3])
 
       request(app)
-      .get('/foo')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, done);
+        .get('/foo')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, done)
     })
 
-    it('should accept nested arrays of middleware', function (done) {
-      var app = express();
+    it('should accept nested arrays of middleware', (done) => {
+      const app = express()
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      function fn3(req, res, next) {
-        res.setHeader('x-fn-3', 'hit');
-        res.end();
+      function fn3 (req, res, next) {
+        res.setHeader('x-fn-3', 'hit')
+        res.end()
       }
 
-      app.use('/foo', [fn1, [fn2]], [fn3]);
+      app.use('/foo', [fn1, [fn2]], [fn3])
 
       request(app)
-      .get('/foo')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, done);
+        .get('/foo')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, done)
     })
 
-    it('should support array of paths', function (done) {
-      var app = express();
-      var cb = after(3, done);
+    it('should support array of paths', (done) => {
+      const app = express()
+      const cb = after(3, done)
 
-      app.use(['/foo/', '/bar'], function (req, res) {
-        res.send('saw ' + req.method + ' ' + req.url + ' through ' + req.originalUrl);
-      });
+      app.use(['/foo/', '/bar'], (req, res) => {
+        res.send('saw ' + req.method + ' ' + req.url + ' through ' + req.originalUrl)
+      })
 
       request(app)
-      .get('/')
-      .expect(404, cb);
+        .get('/')
+        .expect(404, cb)
 
       request(app)
-      .get('/foo')
-      .expect(200, 'saw GET / through /foo', cb);
+        .get('/foo')
+        .expect(200, 'saw GET / through /foo', cb)
 
       request(app)
-      .get('/bar')
-      .expect(200, 'saw GET / through /bar', cb);
+        .get('/bar')
+        .expect(200, 'saw GET / through /bar', cb)
     })
 
-    it('should support array of paths with middleware array', function (done) {
-      var app = express();
-      var cb = after(2, done);
+    it('should support array of paths with middleware array', (done) => {
+      const app = express()
+      const cb = after(2, done)
 
-      function fn1(req, res, next) {
-        res.setHeader('x-fn-1', 'hit');
-        next();
+      function fn1 (req, res, next) {
+        res.setHeader('x-fn-1', 'hit')
+        next()
       }
 
-      function fn2(req, res, next) {
-        res.setHeader('x-fn-2', 'hit');
-        next();
+      function fn2 (req, res, next) {
+        res.setHeader('x-fn-2', 'hit')
+        next()
       }
 
-      function fn3(req, res, next) {
-        res.setHeader('x-fn-3', 'hit');
-        res.send('saw ' + req.method + ' ' + req.url + ' through ' + req.originalUrl);
+      function fn3 (req, res, next) {
+        res.setHeader('x-fn-3', 'hit')
+        res.send('saw ' + req.method + ' ' + req.url + ' through ' + req.originalUrl)
       }
 
-      app.use(['/foo/', '/bar'], [[fn1], fn2], [fn3]);
+      app.use(['/foo/', '/bar'], [[fn1], fn2], [fn3])
 
       request(app)
-      .get('/foo')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, 'saw GET / through /foo', cb);
+        .get('/foo')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, 'saw GET / through /foo', cb)
 
       request(app)
-      .get('/bar')
-      .expect('x-fn-1', 'hit')
-      .expect('x-fn-2', 'hit')
-      .expect('x-fn-3', 'hit')
-      .expect(200, 'saw GET / through /bar', cb);
+        .get('/bar')
+        .expect('x-fn-1', 'hit')
+        .expect('x-fn-2', 'hit')
+        .expect('x-fn-3', 'hit')
+        .expect(200, 'saw GET / through /bar', cb)
     })
 
-    it('should support regexp path', function (done) {
-      var app = express();
-      var cb = after(4, done);
+    it('should support regexp path', (done) => {
+      const app = express()
+      const cb = after(4, done)
 
-      app.use(/^\/[a-z]oo/, function (req, res) {
-        res.send('saw ' + req.method + ' ' + req.url + ' through ' + req.originalUrl);
-      });
+      app.use(/^\/[a-z]oo/, (req, res) => {
+        res.send('saw ' + req.method + ' ' + req.url + ' through ' + req.originalUrl)
+      })
 
       request(app)
-      .get('/')
-      .expect(404, cb);
+        .get('/')
+        .expect(404, cb)
 
       request(app)
-      .get('/foo')
-      .expect(200, 'saw GET / through /foo', cb);
+        .get('/foo')
+        .expect(200, 'saw GET / through /foo', cb)
 
       request(app)
-      .get('/zoo/bear')
-      .expect(200, 'saw GET /bear through /zoo/bear', cb);
+        .get('/zoo/bear')
+        .expect(200, 'saw GET /bear through /zoo/bear', cb)
 
       request(app)
-      .get('/get/zoo')
-      .expect(404, cb);
+        .get('/get/zoo')
+        .expect(404, cb)
     })
 
-    it('should support empty string path', function (done) {
-      var app = express();
+    it('should support empty string path', (done) => {
+      const app = express()
 
-      app.use('', function (req, res) {
-        res.send('saw ' + req.method + ' ' + req.url + ' through ' + req.originalUrl);
-      });
+      app.use('', (req, res) => {
+        res.send('saw ' + req.method + ' ' + req.url + ' through ' + req.originalUrl)
+      })
 
       request(app)
-      .get('/')
-      .expect(200, 'saw GET / through /', done);
+        .get('/')
+        .expect(200, 'saw GET / through /', done)
     })
   })
 })
diff --git a/test/config.js b/test/config.js
index d004de03eaa..d65cc699d00 100644
--- a/test/config.js
+++ b/test/config.js
@@ -1,206 +1,206 @@
 'use strict'
 
-var assert = require('node:assert');
-var express = require('..');
+const assert = require('node:assert')
+const express = require('../')
 
-describe('config', function () {
-  describe('.set()', function () {
-    it('should set a value', function () {
-      var app = express();
-      app.set('foo', 'bar');
-      assert.equal(app.get('foo'), 'bar');
+describe('config', () => {
+  describe('.set()', () => {
+    it('should set a value', () => {
+      const app = express()
+      app.set('foo', 'bar')
+      assert.equal(app.get('foo'), 'bar')
     })
 
-    it('should set prototype values', function () {
-      var app = express()
+    it('should set prototype values', () => {
+      const app = express()
       app.set('hasOwnProperty', 42)
       assert.strictEqual(app.get('hasOwnProperty'), 42)
     })
 
-    it('should return the app', function () {
-      var app = express();
-      assert.equal(app.set('foo', 'bar'), app);
+    it('should return the app', () => {
+      const app = express()
+      assert.equal(app.set('foo', 'bar'), app)
     })
 
-    it('should return the app when undefined', function () {
-      var app = express();
-      assert.equal(app.set('foo', undefined), app);
+    it('should return the app when undefined', () => {
+      const app = express()
+      assert.equal(app.set('foo', undefined), app)
     })
 
-    it('should return set value', function () {
-      var app = express()
+    it('should return set value', () => {
+      const app = express()
       app.set('foo', 'bar')
       assert.strictEqual(app.set('foo'), 'bar')
     })
 
-    it('should return undefined for prototype values', function () {
-      var app = express()
+    it('should return undefined for prototype values', () => {
+      const app = express()
       assert.strictEqual(app.set('hasOwnProperty'), undefined)
     })
 
-    describe('"etag"', function(){
-      it('should throw on bad value', function(){
-        var app = express();
-        assert.throws(app.set.bind(app, 'etag', 42), /unknown value/);
+    describe('"etag"', () => {
+      it('should throw on bad value', () => {
+        const app = express()
+        assert.throws(app.set.bind(app, 'etag', 42), /unknown value/)
       })
 
-      it('should set "etag fn"', function(){
-        var app = express()
-        var fn = function(){}
+      it('should set "etag fn"', () => {
+        const app = express()
+        const fn = function () {}
         app.set('etag', fn)
         assert.equal(app.get('etag fn'), fn)
       })
     })
 
-    describe('"trust proxy"', function(){
-      it('should set "trust proxy fn"', function(){
-        var app = express()
-        var fn = function(){}
+    describe('"trust proxy"', () => {
+      it('should set "trust proxy fn"', () => {
+        const app = express()
+        const fn = function () {}
         app.set('trust proxy', fn)
         assert.equal(app.get('trust proxy fn'), fn)
       })
     })
   })
 
-  describe('.get()', function(){
-    it('should return undefined when unset', function(){
-      var app = express();
-      assert.strictEqual(app.get('foo'), undefined);
+  describe('.get()', () => {
+    it('should return undefined when unset', () => {
+      const app = express()
+      assert.strictEqual(app.get('foo'), undefined)
     })
 
-    it('should return undefined for prototype values', function () {
-      var app = express()
+    it('should return undefined for prototype values', () => {
+      const app = express()
       assert.strictEqual(app.get('hasOwnProperty'), undefined)
     })
 
-    it('should otherwise return the value', function(){
-      var app = express();
-      app.set('foo', 'bar');
-      assert.equal(app.get('foo'), 'bar');
+    it('should otherwise return the value', () => {
+      const app = express()
+      app.set('foo', 'bar')
+      assert.equal(app.get('foo'), 'bar')
     })
 
-    describe('when mounted', function(){
-      it('should default to the parent app', function(){
-        var app = express();
-        var blog = express();
+    describe('when mounted', () => {
+      it('should default to the parent app', () => {
+        const app = express()
+        const blog = express()
 
-        app.set('title', 'Express');
-        app.use(blog);
-        assert.equal(blog.get('title'), 'Express');
+        app.set('title', 'Express')
+        app.use(blog)
+        assert.equal(blog.get('title'), 'Express')
       })
 
-      it('should given precedence to the child', function(){
-        var app = express();
-        var blog = express();
+      it('should given precedence to the child', () => {
+        const app = express()
+        const blog = express()
 
-        app.use(blog);
-        app.set('title', 'Express');
-        blog.set('title', 'Some Blog');
+        app.use(blog)
+        app.set('title', 'Express')
+        blog.set('title', 'Some Blog')
 
-        assert.equal(blog.get('title'), 'Some Blog');
+        assert.equal(blog.get('title'), 'Some Blog')
       })
 
-      it('should inherit "trust proxy" setting', function () {
-        var app = express();
-        var blog = express();
+      it('should inherit "trust proxy" setting', () => {
+        const app = express()
+        const blog = express()
 
-        function fn() { return false }
+        function fn () { return false }
 
-        app.set('trust proxy', fn);
-        assert.equal(app.get('trust proxy'), fn);
-        assert.equal(app.get('trust proxy fn'), fn);
+        app.set('trust proxy', fn)
+        assert.equal(app.get('trust proxy'), fn)
+        assert.equal(app.get('trust proxy fn'), fn)
 
-        app.use(blog);
+        app.use(blog)
 
-        assert.equal(blog.get('trust proxy'), fn);
-        assert.equal(blog.get('trust proxy fn'), fn);
+        assert.equal(blog.get('trust proxy'), fn)
+        assert.equal(blog.get('trust proxy fn'), fn)
       })
 
-      it('should prefer child "trust proxy" setting', function () {
-        var app = express();
-        var blog = express();
+      it('should prefer child "trust proxy" setting', () => {
+        const app = express()
+        const blog = express()
 
-        function fn1() { return false }
-        function fn2() { return true }
+        function fn1 () { return false }
+        function fn2 () { return true }
 
-        app.set('trust proxy', fn1);
-        assert.equal(app.get('trust proxy'), fn1);
-        assert.equal(app.get('trust proxy fn'), fn1);
+        app.set('trust proxy', fn1)
+        assert.equal(app.get('trust proxy'), fn1)
+        assert.equal(app.get('trust proxy fn'), fn1)
 
-        blog.set('trust proxy', fn2);
-        assert.equal(blog.get('trust proxy'), fn2);
-        assert.equal(blog.get('trust proxy fn'), fn2);
+        blog.set('trust proxy', fn2)
+        assert.equal(blog.get('trust proxy'), fn2)
+        assert.equal(blog.get('trust proxy fn'), fn2)
 
-        app.use(blog);
+        app.use(blog)
 
-        assert.equal(app.get('trust proxy'), fn1);
-        assert.equal(app.get('trust proxy fn'), fn1);
-        assert.equal(blog.get('trust proxy'), fn2);
-        assert.equal(blog.get('trust proxy fn'), fn2);
+        assert.equal(app.get('trust proxy'), fn1)
+        assert.equal(app.get('trust proxy fn'), fn1)
+        assert.equal(blog.get('trust proxy'), fn2)
+        assert.equal(blog.get('trust proxy fn'), fn2)
       })
     })
   })
 
-  describe('.enable()', function(){
-    it('should set the value to true', function(){
-      var app = express();
-      assert.equal(app.enable('tobi'), app);
-      assert.strictEqual(app.get('tobi'), true);
+  describe('.enable()', () => {
+    it('should set the value to true', () => {
+      const app = express()
+      assert.equal(app.enable('tobi'), app)
+      assert.strictEqual(app.get('tobi'), true)
     })
 
-    it('should set prototype values', function () {
-      var app = express()
+    it('should set prototype values', () => {
+      const app = express()
       app.enable('hasOwnProperty')
       assert.strictEqual(app.get('hasOwnProperty'), true)
     })
   })
 
-  describe('.disable()', function(){
-    it('should set the value to false', function(){
-      var app = express();
-      assert.equal(app.disable('tobi'), app);
-      assert.strictEqual(app.get('tobi'), false);
+  describe('.disable()', () => {
+    it('should set the value to false', () => {
+      const app = express()
+      assert.equal(app.disable('tobi'), app)
+      assert.strictEqual(app.get('tobi'), false)
     })
 
-    it('should set prototype values', function () {
-      var app = express()
+    it('should set prototype values', () => {
+      const app = express()
       app.disable('hasOwnProperty')
       assert.strictEqual(app.get('hasOwnProperty'), false)
     })
   })
 
-  describe('.enabled()', function(){
-    it('should default to false', function(){
-      var app = express();
-      assert.strictEqual(app.enabled('foo'), false);
+  describe('.enabled()', () => {
+    it('should default to false', () => {
+      const app = express()
+      assert.strictEqual(app.enabled('foo'), false)
     })
 
-    it('should return true when set', function(){
-      var app = express();
-      app.set('foo', 'bar');
-      assert.strictEqual(app.enabled('foo'), true);
+    it('should return true when set', () => {
+      const app = express()
+      app.set('foo', 'bar')
+      assert.strictEqual(app.enabled('foo'), true)
     })
 
-    it('should default to false for prototype values', function () {
-      var app = express()
+    it('should default to false for prototype values', () => {
+      const app = express()
       assert.strictEqual(app.enabled('hasOwnProperty'), false)
     })
   })
 
-  describe('.disabled()', function(){
-    it('should default to true', function(){
-      var app = express();
-      assert.strictEqual(app.disabled('foo'), true);
+  describe('.disabled()', () => {
+    it('should default to true', () => {
+      const app = express()
+      assert.strictEqual(app.disabled('foo'), true)
     })
 
-    it('should return false when set', function(){
-      var app = express();
-      app.set('foo', 'bar');
-      assert.strictEqual(app.disabled('foo'), false);
+    it('should return false when set', () => {
+      const app = express()
+      app.set('foo', 'bar')
+      assert.strictEqual(app.disabled('foo'), false)
     })
 
-    it('should default to true for prototype values', function () {
-      var app = express()
+    it('should default to true for prototype values', () => {
+      const app = express()
       assert.strictEqual(app.disabled('hasOwnProperty'), true)
     })
   })
diff --git a/test/exports.js b/test/exports.js
index fc7836c1594..8c61564a924 100644
--- a/test/exports.js
+++ b/test/exports.js
@@ -1,82 +1,82 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('../');
-var request = require('supertest');
+const assert = require('node:assert')
+const express = require('../')
+const request = require('supertest')
 
-describe('exports', function(){
-  it('should expose Router', function(){
+describe('exports', () => {
+  it('should expose Router', () => {
     assert.strictEqual(typeof express.Router, 'function')
   })
 
-  it('should expose json middleware', function () {
+  it('should expose json middleware', () => {
     assert.equal(typeof express.json, 'function')
     assert.equal(express.json.length, 1)
   })
 
-  it('should expose raw middleware', function () {
+  it('should expose raw middleware', () => {
     assert.equal(typeof express.raw, 'function')
     assert.equal(express.raw.length, 1)
   })
 
-  it('should expose static middleware', function () {
+  it('should expose static middleware', () => {
     assert.equal(typeof express.static, 'function')
     assert.equal(express.static.length, 2)
   })
 
-  it('should expose text middleware', function () {
+  it('should expose text middleware', () => {
     assert.equal(typeof express.text, 'function')
     assert.equal(express.text.length, 1)
   })
 
-  it('should expose urlencoded middleware', function () {
+  it('should expose urlencoded middleware', () => {
     assert.equal(typeof express.urlencoded, 'function')
     assert.equal(express.urlencoded.length, 1)
   })
 
-  it('should expose the application prototype', function(){
+  it('should expose the application prototype', () => {
     assert.strictEqual(typeof express.application, 'object')
     assert.strictEqual(typeof express.application.set, 'function')
   })
 
-  it('should expose the request prototype', function(){
+  it('should expose the request prototype', () => {
     assert.strictEqual(typeof express.request, 'object')
     assert.strictEqual(typeof express.request.accepts, 'function')
   })
 
-  it('should expose the response prototype', function(){
+  it('should expose the response prototype', () => {
     assert.strictEqual(typeof express.response, 'object')
     assert.strictEqual(typeof express.response.send, 'function')
   })
 
-  it('should permit modifying the .application prototype', function(){
-    express.application.foo = function(){ return 'bar'; };
+  it('should permit modifying the .application prototype', () => {
+    express.application.foo = function () { return 'bar' }
     assert.strictEqual(express().foo(), 'bar')
   })
 
-  it('should permit modifying the .request prototype', function(done){
-    express.request.foo = function(){ return 'bar'; };
-    var app = express();
+  it('should permit modifying the .request prototype', (done) => {
+    express.request.foo = function () { return 'bar' }
+    const app = express()
 
-    app.use(function(req, res, next){
-      res.end(req.foo());
-    });
+    app.use((req, res, next) => {
+      res.end(req.foo())
+    })
 
     request(app)
-    .get('/')
-    .expect('bar', done);
+      .get('/')
+      .expect('bar', done)
   })
 
-  it('should permit modifying the .response prototype', function(done){
-    express.response.foo = function(){ this.send('bar'); };
-    var app = express();
+  it('should permit modifying the .response prototype', (done) => {
+    express.response.foo = function () { this.send('bar') }
+    const app = express()
 
-    app.use(function(req, res, next){
-      res.foo();
-    });
+    app.use((req, res, next) => {
+      res.foo()
+    })
 
     request(app)
-    .get('/')
-    .expect('bar', done);
+      .get('/')
+      .expect('bar', done)
   })
 })
diff --git a/test/express.json.js b/test/express.json.js
index 28746bfebda..80ec62e43ae 100644
--- a/test/express.json.js
+++ b/test/express.json.js
@@ -1,14 +1,14 @@
 'use strict'
 
-var assert = require('node:assert')
-var AsyncLocalStorage = require('node:async_hooks').AsyncLocalStorage
-const { Buffer } = require('node:buffer');
+const assert = require('node:assert')
+const { AsyncLocalStorage } = require('node:async_hooks')
+const { Buffer } = require('node:buffer')
 
-var express = require('..')
-var request = require('supertest')
+const express = require('../')
+const request = require('supertest')
 
-describe('express.json()', function () {
-  it('should parse JSON', function (done) {
+describe('express.json()', () => {
+  it('should parse JSON', (done) => {
     request(createApp())
       .post('/')
       .set('Content-Type', 'application/json')
@@ -16,7 +16,7 @@ describe('express.json()', function () {
       .expect(200, '{"user":"tobi"}', done)
   })
 
-  it('should handle Content-Length: 0', function (done) {
+  it('should handle Content-Length: 0', (done) => {
     request(createApp())
       .post('/')
       .set('Content-Type', 'application/json')
@@ -24,7 +24,7 @@ describe('express.json()', function () {
       .expect(200, '{}', done)
   })
 
-  it('should handle empty message-body', function (done) {
+  it('should handle empty message-body', (done) => {
     request(createApp())
       .post('/')
       .set('Content-Type', 'application/json')
@@ -32,7 +32,7 @@ describe('express.json()', function () {
       .expect(200, '{}', done)
   })
 
-  it('should handle no message-body', function (done) {
+  it('should handle no message-body', (done) => {
     request(createApp())
       .post('/')
       .set('Content-Type', 'application/json')
@@ -41,7 +41,7 @@ describe('express.json()', function () {
   })
 
   // The old node error message modification in body parser is catching this
-  it('should 400 when only whitespace', function (done) {
+  it('should 400 when only whitespace', (done) => {
     request(createApp())
       .post('/')
       .set('Content-Type', 'application/json')
@@ -49,17 +49,17 @@ describe('express.json()', function () {
       .expect(400, '[entity.parse.failed] ' + parseError(' \n'), done)
   })
 
-  it('should 400 when invalid content-length', function (done) {
-    var app = express()
+  it('should 400 when invalid content-length', (done) => {
+    const app = express()
 
-    app.use(function (req, res, next) {
+    app.use((req, res, next) => {
       req.headers['content-length'] = '20' // bad length
       next()
     })
 
     app.use(express.json())
 
-    app.post('/', function (req, res) {
+    app.post('/', (req, res) => {
       res.json(req.body)
     })
 
@@ -70,13 +70,13 @@ describe('express.json()', function () {
       .expect(400, /content length/, done)
   })
 
-  it('should handle duplicated middleware', function (done) {
-    var app = express()
+  it('should handle duplicated middleware', (done) => {
+    const app = express()
 
     app.use(express.json())
     app.use(express.json())
 
-    app.post('/', function (req, res) {
+    app.post('/', (req, res) => {
       res.json(req.body)
     })
 
@@ -87,7 +87,7 @@ describe('express.json()', function () {
       .expect(200, '{"user":"tobi"}', done)
   })
 
-  describe('when JSON is invalid', function () {
+  describe('when JSON is invalid', () => {
     before(function () {
       this.app = createApp()
     })
@@ -118,9 +118,9 @@ describe('express.json()', function () {
     })
   })
 
-  describe('with limit option', function () {
-    it('should 413 when over limit with Content-Length', function (done) {
-      var buf = Buffer.alloc(1024, '.')
+  describe('with limit option', () => {
+    it('should 413 when over limit with Content-Length', (done) => {
+      const buf = Buffer.alloc(1024, '.')
       request(createApp({ limit: '1kb' }))
         .post('/')
         .set('Content-Type', 'application/json')
@@ -129,10 +129,10 @@ describe('express.json()', function () {
         .expect(413, '[entity.too.large] request entity too large', done)
     })
 
-    it('should 413 when over limit with chunked encoding', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var buf = Buffer.alloc(1024, '.')
-      var test = request(app).post('/')
+    it('should 413 when over limit with chunked encoding', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const buf = Buffer.alloc(1024, '.')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/json')
       test.set('Transfer-Encoding', 'chunked')
       test.write('{"str":')
@@ -140,17 +140,17 @@ describe('express.json()', function () {
       test.expect(413, done)
     })
 
-    it('should 413 when inflated body over limit', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+    it('should 413 when inflated body over limit', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('1f8b080000000000000aab562a2e2952b252d21b05a360148c58a0540b0066f7ce1e0a040000', 'hex'))
       test.expect(413, done)
     })
 
-    it('should accept number of bytes', function (done) {
-      var buf = Buffer.alloc(1024, '.')
+    it('should accept number of bytes', (done) => {
+      const buf = Buffer.alloc(1024, '.')
       request(createApp({ limit: 1024 }))
         .post('/')
         .set('Content-Type', 'application/json')
@@ -158,10 +158,10 @@ describe('express.json()', function () {
         .expect(413, done)
     })
 
-    it('should not change when options altered', function (done) {
-      var buf = Buffer.alloc(1024, '.')
-      var options = { limit: '1kb' }
-      var app = createApp(options)
+    it('should not change when options altered', (done) => {
+      const buf = Buffer.alloc(1024, '.')
+      const options = { limit: '1kb' }
+      const app = createApp(options)
 
       options.limit = '100kb'
 
@@ -172,10 +172,10 @@ describe('express.json()', function () {
         .expect(413, done)
     })
 
-    it('should not hang response', function (done) {
-      var buf = Buffer.alloc(10240, '.')
-      var app = createApp({ limit: '8kb' })
-      var test = request(app).post('/')
+    it('should not hang response', (done) => {
+      const buf = Buffer.alloc(10240, '.')
+      const app = createApp({ limit: '8kb' })
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/json')
       test.write(buf)
       test.write(buf)
@@ -183,9 +183,9 @@ describe('express.json()', function () {
       test.expect(413, done)
     })
 
-    it('should not error when inflating', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+    it('should not error when inflating', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('1f8b080000000000000aab562a2e2952b252d21b05a360148c58a0540b0066f7ce1e0a0400', 'hex'))
@@ -193,14 +193,14 @@ describe('express.json()', function () {
     })
   })
 
-  describe('with inflate option', function () {
-    describe('when false', function () {
+  describe('with inflate option', () => {
+    describe('when false', () => {
       before(function () {
         this.app = createApp({ inflate: false })
       })
 
       it('should not accept content-encoding', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Encoding', 'gzip')
         test.set('Content-Type', 'application/json')
         test.write(Buffer.from('1f8b080000000000000bab56ca4bcc4d55b2527ab16e97522d00515be1cc0e000000', 'hex'))
@@ -208,13 +208,13 @@ describe('express.json()', function () {
       })
     })
 
-    describe('when true', function () {
+    describe('when true', () => {
       before(function () {
         this.app = createApp({ inflate: true })
       })
 
       it('should accept content-encoding', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Encoding', 'gzip')
         test.set('Content-Type', 'application/json')
         test.write(Buffer.from('1f8b080000000000000bab56ca4bcc4d55b2527ab16e97522d00515be1cc0e000000', 'hex'))
@@ -223,8 +223,8 @@ describe('express.json()', function () {
     })
   })
 
-  describe('with strict option', function () {
-    describe('when undefined', function () {
+  describe('with strict option', () => {
+    describe('when undefined', () => {
       before(function () {
         this.app = createApp()
       })
@@ -238,7 +238,7 @@ describe('express.json()', function () {
       })
     })
 
-    describe('when false', function () {
+    describe('when false', () => {
       before(function () {
         this.app = createApp({ strict: false })
       })
@@ -252,7 +252,7 @@ describe('express.json()', function () {
       })
     })
 
-    describe('when true', function () {
+    describe('when true', () => {
       before(function () {
         this.app = createApp({ strict: true })
       })
@@ -294,8 +294,8 @@ describe('express.json()', function () {
     })
   })
 
-  describe('with type option', function () {
-    describe('when "application/vnd.api+json"', function () {
+  describe('with type option', () => {
+    describe('when "application/vnd.api+json"', () => {
       before(function () {
         this.app = createApp({ type: 'application/vnd.api+json' })
       })
@@ -317,7 +317,7 @@ describe('express.json()', function () {
       })
     })
 
-    describe('when ["application/json", "application/vnd.api+json"]', function () {
+    describe('when ["application/json", "application/vnd.api+json"]', () => {
       before(function () {
         this.app = createApp({
           type: ['application/json', 'application/vnd.api+json']
@@ -349,9 +349,9 @@ describe('express.json()', function () {
       })
     })
 
-    describe('when a function', function () {
-      it('should parse when truthy value returned', function (done) {
-        var app = createApp({ type: accept })
+    describe('when a function', () => {
+      it('should parse when truthy value returned', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           return req.headers['content-type'] === 'application/vnd.api+json'
@@ -364,20 +364,20 @@ describe('express.json()', function () {
           .expect(200, '{"user":"tobi"}', done)
       })
 
-      it('should work without content-type', function (done) {
-        var app = createApp({ type: accept })
+      it('should work without content-type', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           return true
         }
 
-        var test = request(app).post('/')
+        const test = request(app).post('/')
         test.write('{"user":"tobi"}')
         test.expect(200, '{"user":"tobi"}', done)
       })
 
-      it('should not invoke without a body', function (done) {
-        var app = createApp({ type: accept })
+      it('should not invoke without a body', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           throw new Error('oops!')
@@ -390,14 +390,14 @@ describe('express.json()', function () {
     })
   })
 
-  describe('with verify option', function () {
-    it('should assert value if function', function () {
+  describe('with verify option', () => {
+    it('should assert value if function', () => {
       assert.throws(createApp.bind(null, { verify: 'lol' }),
         /TypeError: option verify must be function/)
     })
 
-    it('should error from verify', function (done) {
-      var app = createApp({
+    it('should error from verify', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x5b) throw new Error('no arrays')
         }
@@ -410,11 +410,11 @@ describe('express.json()', function () {
         .expect(403, '[entity.verify.failed] no arrays', done)
     })
 
-    it('should allow custom codes', function (done) {
-      var app = createApp({
+    it('should allow custom codes', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] !== 0x5b) return
-          var err = new Error('no arrays')
+          const err = new Error('no arrays')
           err.status = 400
           throw err
         }
@@ -427,11 +427,11 @@ describe('express.json()', function () {
         .expect(400, '[entity.verify.failed] no arrays', done)
     })
 
-    it('should allow custom type', function (done) {
-      var app = createApp({
+    it('should allow custom type', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] !== 0x5b) return
-          var err = new Error('no arrays')
+          const err = new Error('no arrays')
           err.type = 'foo.bar'
           throw err
         }
@@ -444,8 +444,8 @@ describe('express.json()', function () {
         .expect(403, '[foo.bar] no arrays', done)
     })
 
-    it('should include original body on error object', function (done) {
-      var app = createApp({
+    it('should include original body on error object', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x5b) throw new Error('no arrays')
         }
@@ -459,8 +459,8 @@ describe('express.json()', function () {
         .expect(403, '["tobi"]', done)
     })
 
-    it('should allow pass-through', function (done) {
-      var app = createApp({
+    it('should allow pass-through', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x5b) throw new Error('no arrays')
         }
@@ -473,47 +473,47 @@ describe('express.json()', function () {
         .expect(200, '{"user":"tobi"}', done)
     })
 
-    it('should work with different charsets', function (done) {
-      var app = createApp({
+    it('should work with different charsets', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x5b) throw new Error('no arrays')
         }
       })
 
-      var test = request(app).post('/')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/json; charset=utf-16')
       test.write(Buffer.from('feff007b0022006e0061006d00650022003a00228bba0022007d', 'hex'))
       test.expect(200, '{"name":"论"}', done)
     })
 
-    it('should 415 on unknown charset prior to verify', function (done) {
-      var app = createApp({
+    it('should 415 on unknown charset prior to verify', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           throw new Error('unexpected verify call')
         }
       })
 
-      var test = request(app).post('/')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/json; charset=x-bogus')
       test.write(Buffer.from('00000000', 'hex'))
       test.expect(415, '[charset.unsupported] unsupported charset "X-BOGUS"', done)
     })
   })
 
-  describe('async local storage', function () {
+  describe('async local storage', () => {
     before(function () {
-      var app = express()
-      var store = { foo: 'bar' }
+      const app = express()
+      const store = { foo: 'bar' }
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         req.asyncLocalStorage = new AsyncLocalStorage()
         req.asyncLocalStorage.run(store, next)
       })
 
       app.use(express.json())
 
-      app.use(function (req, res, next) {
-        var local = req.asyncLocalStorage.getStore()
+      app.use((req, res, next) => {
+        const local = req.asyncLocalStorage.getStore()
 
         if (local) {
           res.setHeader('x-store-foo', String(local.foo))
@@ -522,8 +522,8 @@ describe('express.json()', function () {
         next()
       })
 
-      app.use(function (err, req, res, next) {
-        var local = req.asyncLocalStorage.getStore()
+      app.use((err, req, res, next) => {
+        const local = req.asyncLocalStorage.getStore()
 
         if (local) {
           res.setHeader('x-store-foo', String(local.foo))
@@ -533,7 +533,7 @@ describe('express.json()', function () {
         res.send('[' + err.type + '] ' + err.message)
       })
 
-      app.post('/', function (req, res) {
+      app.post('/', (req, res) => {
         res.json(req.body)
       })
 
@@ -563,7 +563,7 @@ describe('express.json()', function () {
     })
 
     it('should persist store when inflated', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('1f8b080000000000000bab56ca4bcc4d55b2527ab16e97522d00515be1cc0e000000', 'hex'))
@@ -574,7 +574,7 @@ describe('express.json()', function () {
     })
 
     it('should persist store when inflate error', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('1f8b080000000000000bab56cc4d55b2527ab16e97522d00515be1cc0e000000', 'hex'))
@@ -604,27 +604,27 @@ describe('express.json()', function () {
     })
   })
 
-  describe('charset', function () {
+  describe('charset', () => {
     before(function () {
       this.app = createApp()
     })
 
     it('should parse utf-8', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/json; charset=utf-8')
       test.write(Buffer.from('7b226e616d65223a22e8aeba227d', 'hex'))
       test.expect(200, '{"name":"论"}', done)
     })
 
     it('should parse utf-16', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/json; charset=utf-16')
       test.write(Buffer.from('feff007b0022006e0061006d00650022003a00228bba0022007d', 'hex'))
       test.expect(200, '{"name":"论"}', done)
     })
 
     it('should parse when content-length != char length', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/json; charset=utf-8')
       test.set('Content-Length', '13')
       test.write(Buffer.from('7b2274657374223a22c3a5227d', 'hex'))
@@ -632,34 +632,34 @@ describe('express.json()', function () {
     })
 
     it('should default to utf-8', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('7b226e616d65223a22e8aeba227d', 'hex'))
       test.expect(200, '{"name":"论"}', done)
     })
 
     it('should fail on unknown charset', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/json; charset=koi8-r')
       test.write(Buffer.from('7b226e616d65223a22cec5d4227d', 'hex'))
       test.expect(415, '[charset.unsupported] unsupported charset "KOI8-R"', done)
     })
   })
 
-  describe('encoding', function () {
+  describe('encoding', () => {
     before(function () {
       this.app = createApp({ limit: '1kb' })
     })
 
     it('should parse without encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('7b226e616d65223a22e8aeba227d', 'hex'))
       test.expect(200, '{"name":"论"}', done)
     })
 
     it('should support identity encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'identity')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('7b226e616d65223a22e8aeba227d', 'hex'))
@@ -667,7 +667,7 @@ describe('express.json()', function () {
     })
 
     it('should support gzip encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('1f8b080000000000000bab56ca4bcc4d55b2527ab16e97522d00515be1cc0e000000', 'hex'))
@@ -675,7 +675,7 @@ describe('express.json()', function () {
     })
 
     it('should support deflate encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'deflate')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('789cab56ca4bcc4d55b2527ab16e97522d00274505ac', 'hex'))
@@ -683,7 +683,7 @@ describe('express.json()', function () {
     })
 
     it('should be case-insensitive', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'GZIP')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('1f8b080000000000000bab56ca4bcc4d55b2527ab16e97522d00515be1cc0e000000', 'hex'))
@@ -691,7 +691,7 @@ describe('express.json()', function () {
     })
 
     it('should 415 on unknown encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'nulls')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('000000000000', 'hex'))
@@ -699,7 +699,7 @@ describe('express.json()', function () {
     })
 
     it('should 400 on malformed encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('1f8b080000000000000bab56cc4d55b2527ab16e97522d00515be1cc0e000000', 'hex'))
@@ -708,7 +708,7 @@ describe('express.json()', function () {
 
     it('should 413 when inflated value exceeds limit', function (done) {
       // gzip'd data exceeds 1kb, but deflated below 1kb
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/json')
       test.write(Buffer.from('1f8b080000000000000bedc1010d000000c2a0f74f6d0f071400000000000000', 'hex'))
@@ -720,11 +720,11 @@ describe('express.json()', function () {
 })
 
 function createApp (options) {
-  var app = express()
+  const app = express()
 
   app.use(express.json(options))
 
-  app.use(function (err, req, res, next) {
+  app.use((err, req, res, next) => {
     // console.log(err)
     res.status(err.status || 500)
     res.send(String(req.headers['x-error-property']
@@ -732,7 +732,7 @@ function createApp (options) {
       : ('[' + err.type + '] ' + err.message)))
   })
 
-  app.post('/', function (req, res) {
+  app.post('/', (req, res) => {
     res.json(req.body)
   })
 
diff --git a/test/express.raw.js b/test/express.raw.js
index 5576e225283..488c1122cc6 100644
--- a/test/express.raw.js
+++ b/test/express.raw.js
@@ -1,13 +1,13 @@
 'use strict'
 
-var assert = require('node:assert')
-var AsyncLocalStorage = require('node:async_hooks').AsyncLocalStorage
+const assert = require('node:assert')
+const { AsyncLocalStorage } = require('node:async_hooks')
 
-var express = require('..')
-var request = require('supertest')
-const { Buffer } = require('node:buffer');
+const express = require('../')
+const request = require('supertest')
+const { Buffer } = require('node:buffer')
 
-describe('express.raw()', function () {
+describe('express.raw()', () => {
   before(function () {
     this.app = createApp()
   })
@@ -20,17 +20,17 @@ describe('express.raw()', function () {
       .expect(200, { buf: '746865207573657220697320746f6269' }, done)
   })
 
-  it('should 400 when invalid content-length', function (done) {
-    var app = express()
+  it('should 400 when invalid content-length', (done) => {
+    const app = express()
 
-    app.use(function (req, res, next) {
+    app.use((req, res, next) => {
       req.headers['content-length'] = '20' // bad length
       next()
     })
 
     app.use(express.raw())
 
-    app.post('/', function (req, res) {
+    app.post('/', (req, res) => {
       if (Buffer.isBuffer(req.body)) {
         res.json({ buf: req.body.toString('hex') })
       } else {
@@ -62,13 +62,13 @@ describe('express.raw()', function () {
       .expect(200, { buf: '' }, done)
   })
 
-  it('should handle duplicated middleware', function (done) {
-    var app = express()
+  it('should handle duplicated middleware', (done) => {
+    const app = express()
 
     app.use(express.raw())
     app.use(express.raw())
 
-    app.post('/', function (req, res) {
+    app.post('/', (req, res) => {
       if (Buffer.isBuffer(req.body)) {
         res.json({ buf: req.body.toString('hex') })
       } else {
@@ -83,62 +83,62 @@ describe('express.raw()', function () {
       .expect(200, { buf: '746865207573657220697320746f6269' }, done)
   })
 
-  describe('with limit option', function () {
-    it('should 413 when over limit with Content-Length', function (done) {
-      var buf = Buffer.alloc(1028, '.')
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+  describe('with limit option', () => {
+    it('should 413 when over limit with Content-Length', (done) => {
+      const buf = Buffer.alloc(1028, '.')
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/octet-stream')
       test.set('Content-Length', '1028')
       test.write(buf)
       test.expect(413, done)
     })
 
-    it('should 413 when over limit with chunked encoding', function (done) {
-      var buf = Buffer.alloc(1028, '.')
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+    it('should 413 when over limit with chunked encoding', (done) => {
+      const buf = Buffer.alloc(1028, '.')
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/octet-stream')
       test.set('Transfer-Encoding', 'chunked')
       test.write(buf)
       test.expect(413, done)
     })
 
-    it('should 413 when inflated body over limit', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+    it('should 413 when inflated body over limit', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('1f8b080000000000000ad3d31b05a360148c64000087e5a14704040000', 'hex'))
       test.expect(413, done)
     })
 
-    it('should accept number of bytes', function (done) {
-      var buf = Buffer.alloc(1028, '.')
-      var app = createApp({ limit: 1024 })
-      var test = request(app).post('/')
+    it('should accept number of bytes', (done) => {
+      const buf = Buffer.alloc(1028, '.')
+      const app = createApp({ limit: 1024 })
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/octet-stream')
       test.write(buf)
       test.expect(413, done)
     })
 
-    it('should not change when options altered', function (done) {
-      var buf = Buffer.alloc(1028, '.')
-      var options = { limit: '1kb' }
-      var app = createApp(options)
+    it('should not change when options altered', (done) => {
+      const buf = Buffer.alloc(1028, '.')
+      const options = { limit: '1kb' }
+      const app = createApp(options)
 
       options.limit = '100kb'
 
-      var test = request(app).post('/')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/octet-stream')
       test.write(buf)
       test.expect(413, done)
     })
 
-    it('should not hang response', function (done) {
-      var buf = Buffer.alloc(10240, '.')
-      var app = createApp({ limit: '8kb' })
-      var test = request(app).post('/')
+    it('should not hang response', (done) => {
+      const buf = Buffer.alloc(10240, '.')
+      const app = createApp({ limit: '8kb' })
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/octet-stream')
       test.write(buf)
       test.write(buf)
@@ -146,9 +146,9 @@ describe('express.raw()', function () {
       test.expect(413, done)
     })
 
-    it('should not error when inflating', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+    it('should not error when inflating', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('1f8b080000000000000ad3d31b05a360148c64000087e5a147040400', 'hex'))
@@ -156,14 +156,14 @@ describe('express.raw()', function () {
     })
   })
 
-  describe('with inflate option', function () {
-    describe('when false', function () {
+  describe('with inflate option', () => {
+    describe('when false', () => {
       before(function () {
         this.app = createApp({ inflate: false })
       })
 
       it('should not accept content-encoding', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Encoding', 'gzip')
         test.set('Content-Type', 'application/octet-stream')
         test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -171,13 +171,13 @@ describe('express.raw()', function () {
       })
     })
 
-    describe('when true', function () {
+    describe('when true', () => {
       before(function () {
         this.app = createApp({ inflate: true })
       })
 
       it('should accept content-encoding', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Encoding', 'gzip')
         test.set('Content-Type', 'application/octet-stream')
         test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -186,28 +186,28 @@ describe('express.raw()', function () {
     })
   })
 
-  describe('with type option', function () {
-    describe('when "application/vnd+octets"', function () {
+  describe('with type option', () => {
+    describe('when "application/vnd+octets"', () => {
       before(function () {
         this.app = createApp({ type: 'application/vnd+octets' })
       })
 
       it('should parse for custom type', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Type', 'application/vnd+octets')
         test.write(Buffer.from('000102', 'hex'))
         test.expect(200, { buf: '000102' }, done)
       })
 
       it('should ignore standard type', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Type', 'application/octet-stream')
         test.write(Buffer.from('000102', 'hex'))
         test.expect(200, '', done)
       })
     })
 
-    describe('when ["application/octet-stream", "application/vnd+octets"]', function () {
+    describe('when ["application/octet-stream", "application/vnd+octets"]', () => {
       before(function () {
         this.app = createApp({
           type: ['application/octet-stream', 'application/vnd+octets']
@@ -215,55 +215,55 @@ describe('express.raw()', function () {
       })
 
       it('should parse "application/octet-stream"', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Type', 'application/octet-stream')
         test.write(Buffer.from('000102', 'hex'))
         test.expect(200, { buf: '000102' }, done)
       })
 
       it('should parse "application/vnd+octets"', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Type', 'application/vnd+octets')
         test.write(Buffer.from('000102', 'hex'))
         test.expect(200, { buf: '000102' }, done)
       })
 
       it('should ignore "application/x-foo"', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Type', 'application/x-foo')
         test.write(Buffer.from('000102', 'hex'))
         test.expect(200, '', done)
       })
     })
 
-    describe('when a function', function () {
-      it('should parse when truthy value returned', function (done) {
-        var app = createApp({ type: accept })
+    describe('when a function', () => {
+      it('should parse when truthy value returned', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           return req.headers['content-type'] === 'application/vnd.octet'
         }
 
-        var test = request(app).post('/')
+        const test = request(app).post('/')
         test.set('Content-Type', 'application/vnd.octet')
         test.write(Buffer.from('000102', 'hex'))
         test.expect(200, { buf: '000102' }, done)
       })
 
-      it('should work without content-type', function (done) {
-        var app = createApp({ type: accept })
+      it('should work without content-type', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           return true
         }
 
-        var test = request(app).post('/')
+        const test = request(app).post('/')
         test.write(Buffer.from('000102', 'hex'))
         test.expect(200, { buf: '000102' }, done)
       })
 
-      it('should not invoke without a body', function (done) {
-        var app = createApp({ type: accept })
+      it('should not invoke without a body', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           throw new Error('oops!')
@@ -276,69 +276,69 @@ describe('express.raw()', function () {
     })
   })
 
-  describe('with verify option', function () {
-    it('should assert value is function', function () {
+  describe('with verify option', () => {
+    it('should assert value is function', () => {
       assert.throws(createApp.bind(null, { verify: 'lol' }),
         /TypeError: option verify must be function/)
     })
 
-    it('should error from verify', function (done) {
-      var app = createApp({
+    it('should error from verify', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x00) throw new Error('no leading null')
         }
       })
 
-      var test = request(app).post('/')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('000102', 'hex'))
       test.expect(403, '[entity.verify.failed] no leading null', done)
     })
 
-    it('should allow custom codes', function (done) {
-      var app = createApp({
+    it('should allow custom codes', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] !== 0x00) return
-          var err = new Error('no leading null')
+          const err = new Error('no leading null')
           err.status = 400
           throw err
         }
       })
 
-      var test = request(app).post('/')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('000102', 'hex'))
       test.expect(400, '[entity.verify.failed] no leading null', done)
     })
 
-    it('should allow pass-through', function (done) {
-      var app = createApp({
+    it('should allow pass-through', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x00) throw new Error('no leading null')
         }
       })
 
-      var test = request(app).post('/')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('0102', 'hex'))
       test.expect(200, { buf: '0102' }, done)
     })
   })
 
-  describe('async local storage', function () {
+  describe('async local storage', () => {
     before(function () {
-      var app = express()
-      var store = { foo: 'bar' }
+      const app = express()
+      const store = { foo: 'bar' }
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         req.asyncLocalStorage = new AsyncLocalStorage()
         req.asyncLocalStorage.run(store, next)
       })
 
       app.use(express.raw())
 
-      app.use(function (req, res, next) {
-        var local = req.asyncLocalStorage.getStore()
+      app.use((req, res, next) => {
+        const local = req.asyncLocalStorage.getStore()
 
         if (local) {
           res.setHeader('x-store-foo', String(local.foo))
@@ -347,8 +347,8 @@ describe('express.raw()', function () {
         next()
       })
 
-      app.use(function (err, req, res, next) {
-        var local = req.asyncLocalStorage.getStore()
+      app.use((err, req, res, next) => {
+        const local = req.asyncLocalStorage.getStore()
 
         if (local) {
           res.setHeader('x-store-foo', String(local.foo))
@@ -358,7 +358,7 @@ describe('express.raw()', function () {
         res.send('[' + err.type + '] ' + err.message)
       })
 
-      app.post('/', function (req, res) {
+      app.post('/', (req, res) => {
         if (Buffer.isBuffer(req.body)) {
           res.json({ buf: req.body.toString('hex') })
         } else {
@@ -391,7 +391,7 @@ describe('express.raw()', function () {
     })
 
     it('should persist store when inflated', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -402,7 +402,7 @@ describe('express.raw()', function () {
     })
 
     it('should persist store when inflate error', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad6080000', 'hex'))
@@ -422,33 +422,33 @@ describe('express.raw()', function () {
     })
   })
 
-  describe('charset', function () {
+  describe('charset', () => {
     before(function () {
       this.app = createApp()
     })
 
     it('should ignore charset', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/octet-stream; charset=utf-8')
       test.write(Buffer.from('6e616d6520697320e8aeba', 'hex'))
       test.expect(200, { buf: '6e616d6520697320e8aeba' }, done)
     })
   })
 
-  describe('encoding', function () {
+  describe('encoding', () => {
     before(function () {
       this.app = createApp({ limit: '10kb' })
     })
 
     it('should parse without encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('6e616d653de8aeba', 'hex'))
       test.expect(200, { buf: '6e616d653de8aeba' }, done)
     })
 
     it('should support identity encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'identity')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('6e616d653de8aeba', 'hex'))
@@ -456,7 +456,7 @@ describe('express.raw()', function () {
     })
 
     it('should support gzip encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -464,7 +464,7 @@ describe('express.raw()', function () {
     })
 
     it('should support deflate encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'deflate')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('789ccb4bcc4db57db16e17001068042f', 'hex'))
@@ -472,7 +472,7 @@ describe('express.raw()', function () {
     })
 
     it('should be case-insensitive', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'GZIP')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -480,7 +480,7 @@ describe('express.raw()', function () {
     })
 
     it('should 415 on unknown encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'nulls')
       test.set('Content-Type', 'application/octet-stream')
       test.write(Buffer.from('000000000000', 'hex'))
@@ -490,18 +490,18 @@ describe('express.raw()', function () {
 })
 
 function createApp (options) {
-  var app = express()
+  const app = express()
 
   app.use(express.raw(options))
 
-  app.use(function (err, req, res, next) {
+  app.use((err, req, res, next) => {
     res.status(err.status || 500)
     res.send(String(req.headers['x-error-property']
       ? err[req.headers['x-error-property']]
       : ('[' + err.type + '] ' + err.message)))
   })
 
-  app.post('/', function (req, res) {
+  app.post('/', (req, res) => {
     if (Buffer.isBuffer(req.body)) {
       res.json({ buf: req.body.toString('hex') })
     } else {
diff --git a/test/express.static.js b/test/express.static.js
index a2035631d66..2ec2acb75de 100644
--- a/test/express.static.js
+++ b/test/express.static.js
@@ -1,29 +1,29 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('..')
-var path = require('node:path')
-const { Buffer } = require('node:buffer');
+const assert = require('node:assert')
+const express = require('../')
+const path = require('node:path')
+const { Buffer } = require('node:buffer')
 
-var request = require('supertest')
-var utils = require('./support/utils')
+const request = require('supertest')
+const utils = require('./support/utils')
 
-var fixtures = path.join(__dirname, '/fixtures')
-var relative = path.relative(process.cwd(), fixtures)
+const fixtures = path.join(__dirname, '/fixtures')
+const relative = path.relative(process.cwd(), fixtures)
 
-var skipRelative = ~relative.indexOf('..') || path.resolve(relative) === relative
+const skipRelative = ~relative.indexOf('..') || path.resolve(relative) === relative
 
-describe('express.static()', function () {
-  describe('basic operations', function () {
+describe('express.static()', () => {
+  describe('basic operations', () => {
     before(function () {
       this.app = createApp()
     })
 
-    it('should require root path', function () {
+    it('should require root path', () => {
       assert.throws(express.static.bind(), /root path required/)
     })
 
-    it('should require root path to be string', function () {
+    it('should require root path to be string', () => {
       assert.throws(express.static.bind(null, 42), /root path.*string/)
     })
 
@@ -101,11 +101,11 @@ describe('express.static()', function () {
     })
 
     it('should support conditional requests', function (done) {
-      var app = this.app
+      const app = this.app
 
       request(app)
         .get('/todo.txt')
-        .end(function (err, res) {
+        .end((err, res) => {
           if (err) throw err
           request(app)
             .get('/todo.txt')
@@ -134,30 +134,30 @@ describe('express.static()', function () {
     })
   });
 
-  (skipRelative ? describe.skip : describe)('current dir', function () {
+  (skipRelative ? describe.skip : describe)('current dir', () => {
     before(function () {
       this.app = createApp('.')
     })
 
     it('should be served with "."', function (done) {
-      var dest = relative.split(path.sep).join('/')
+      const dest = relative.split(path.sep).join('/')
       request(this.app)
         .get('/' + dest + '/todo.txt')
         .expect(200, '- groceries', done)
     })
   })
 
-  describe('acceptRanges', function () {
-    describe('when false', function () {
-      it('should not include Accept-Ranges', function (done) {
-        request(createApp(fixtures, { 'acceptRanges': false }))
+  describe('acceptRanges', () => {
+    describe('when false', () => {
+      it('should not include Accept-Ranges', (done) => {
+        request(createApp(fixtures, { acceptRanges: false }))
           .get('/nums.txt')
           .expect(utils.shouldNotHaveHeader('Accept-Ranges'))
           .expect(200, '123456789', done)
       })
 
-      it('should ignore Rage request header', function (done) {
-        request(createApp(fixtures, { 'acceptRanges': false }))
+      it('should ignore Rage request header', (done) => {
+        request(createApp(fixtures, { acceptRanges: false }))
           .get('/nums.txt')
           .set('Range', 'bytes=0-3')
           .expect(utils.shouldNotHaveHeader('Accept-Ranges'))
@@ -166,16 +166,16 @@ describe('express.static()', function () {
       })
     })
 
-    describe('when true', function () {
-      it('should include Accept-Ranges', function (done) {
-        request(createApp(fixtures, { 'acceptRanges': true }))
+    describe('when true', () => {
+      it('should include Accept-Ranges', (done) => {
+        request(createApp(fixtures, { acceptRanges: true }))
           .get('/nums.txt')
           .expect('Accept-Ranges', 'bytes')
           .expect(200, '123456789', done)
       })
 
-      it('should obey Rage request header', function (done) {
-        request(createApp(fixtures, { 'acceptRanges': true }))
+      it('should obey Rage request header', (done) => {
+        request(createApp(fixtures, { acceptRanges: true }))
           .get('/nums.txt')
           .set('Range', 'bytes=0-3')
           .expect('Accept-Ranges', 'bytes')
@@ -185,26 +185,26 @@ describe('express.static()', function () {
     })
   })
 
-  describe('cacheControl', function () {
-    describe('when false', function () {
-      it('should not include Cache-Control', function (done) {
-        request(createApp(fixtures, { 'cacheControl': false }))
+  describe('cacheControl', () => {
+    describe('when false', () => {
+      it('should not include Cache-Control', (done) => {
+        request(createApp(fixtures, { cacheControl: false }))
           .get('/nums.txt')
           .expect(utils.shouldNotHaveHeader('Cache-Control'))
           .expect(200, '123456789', done)
       })
 
-      it('should ignore maxAge', function (done) {
-        request(createApp(fixtures, { 'cacheControl': false, 'maxAge': 12000 }))
+      it('should ignore maxAge', (done) => {
+        request(createApp(fixtures, { cacheControl: false, maxAge: 12000 }))
           .get('/nums.txt')
           .expect(utils.shouldNotHaveHeader('Cache-Control'))
           .expect(200, '123456789', done)
       })
     })
 
-    describe('when true', function () {
-      it('should include Cache-Control', function (done) {
-        request(createApp(fixtures, { 'cacheControl': true }))
+    describe('when true', () => {
+      it('should include Cache-Control', (done) => {
+        request(createApp(fixtures, { cacheControl: true }))
           .get('/nums.txt')
           .expect('Cache-Control', 'public, max-age=0')
           .expect(200, '123456789', done)
@@ -212,48 +212,48 @@ describe('express.static()', function () {
     })
   })
 
-  describe('extensions', function () {
-    it('should be not be enabled by default', function (done) {
+  describe('extensions', () => {
+    it('should be not be enabled by default', (done) => {
       request(createApp(fixtures))
         .get('/todo')
         .expect(404, done)
     })
 
-    it('should be configurable', function (done) {
-      request(createApp(fixtures, { 'extensions': 'txt' }))
+    it('should be configurable', (done) => {
+      request(createApp(fixtures, { extensions: 'txt' }))
         .get('/todo')
         .expect(200, '- groceries', done)
     })
 
-    it('should support disabling extensions', function (done) {
-      request(createApp(fixtures, { 'extensions': false }))
+    it('should support disabling extensions', (done) => {
+      request(createApp(fixtures, { extensions: false }))
         .get('/todo')
         .expect(404, done)
     })
 
-    it('should support fallbacks', function (done) {
-      request(createApp(fixtures, { 'extensions': ['htm', 'html', 'txt'] }))
+    it('should support fallbacks', (done) => {
+      request(createApp(fixtures, { extensions: ['htm', 'html', 'txt'] }))
         .get('/todo')
         .expect(200, '<li>groceries</li>', done)
     })
 
-    it('should 404 if nothing found', function (done) {
-      request(createApp(fixtures, { 'extensions': ['htm', 'html', 'txt'] }))
+    it('should 404 if nothing found', (done) => {
+      request(createApp(fixtures, { extensions: ['htm', 'html', 'txt'] }))
         .get('/bob')
         .expect(404, done)
     })
   })
 
-  describe('fallthrough', function () {
-    it('should default to true', function (done) {
+  describe('fallthrough', () => {
+    it('should default to true', (done) => {
       request(createApp())
         .get('/does-not-exist')
         .expect(404, 'Not Found', done)
     })
 
-    describe('when true', function () {
+    describe('when true', () => {
       before(function () {
-        this.app = createApp(fixtures, { 'fallthrough': true })
+        this.app = createApp(fixtures, { fallthrough: true })
       })
 
       it('should fall-through when OPTIONS request', function (done) {
@@ -274,12 +274,12 @@ describe('express.static()', function () {
           .expect(404, 'Not Found', done)
       })
 
-      it('should fall-through when URL too long', function (done) {
-        var app = express()
-        var root = fixtures + Array(10000).join('/foobar')
+      it('should fall-through when URL too long', (done) => {
+        const app = express()
+        const root = fixtures + Array(10000).join('/foobar')
 
-        app.use(express.static(root, { 'fallthrough': true }))
-        app.use(function (req, res, next) {
+        app.use(express.static(root, { fallthrough: true }))
+        app.use((req, res, next) => {
           res.sendStatus(404)
         })
 
@@ -288,9 +288,9 @@ describe('express.static()', function () {
           .expect(404, 'Not Found', done)
       })
 
-      describe('with redirect: true', function () {
+      describe('with redirect: true', () => {
         before(function () {
-          this.app = createApp(fixtures, { 'fallthrough': true, 'redirect': true })
+          this.app = createApp(fixtures, { fallthrough: true, redirect: true })
         })
 
         it('should fall-through when directory', function (done) {
@@ -306,9 +306,9 @@ describe('express.static()', function () {
         })
       })
 
-      describe('with redirect: false', function () {
+      describe('with redirect: false', () => {
         before(function () {
-          this.app = createApp(fixtures, { 'fallthrough': true, 'redirect': false })
+          this.app = createApp(fixtures, { fallthrough: true, redirect: false })
         })
 
         it('should fall-through when directory', function (done) {
@@ -325,9 +325,9 @@ describe('express.static()', function () {
       })
     })
 
-    describe('when false', function () {
+    describe('when false', () => {
       before(function () {
-        this.app = createApp(fixtures, { 'fallthrough': false })
+        this.app = createApp(fixtures, { fallthrough: false })
       })
 
       it('should 405 when OPTIONS request', function (done) {
@@ -349,12 +349,12 @@ describe('express.static()', function () {
           .expect(403, /ForbiddenError/, done)
       })
 
-      it('should 404 when URL too long', function (done) {
-        var app = express()
-        var root = fixtures + Array(10000).join('/foobar')
+      it('should 404 when URL too long', (done) => {
+        const app = express()
+        const root = fixtures + Array(10000).join('/foobar')
 
-        app.use(express.static(root, { 'fallthrough': false }))
-        app.use(function (req, res, next) {
+        app.use(express.static(root, { fallthrough: false }))
+        app.use((req, res, next) => {
           res.sendStatus(404)
         })
 
@@ -363,9 +363,9 @@ describe('express.static()', function () {
           .expect(404, /ENAMETOOLONG/, done)
       })
 
-      describe('with redirect: true', function () {
+      describe('with redirect: true', () => {
         before(function () {
-          this.app = createApp(fixtures, { 'fallthrough': false, 'redirect': true })
+          this.app = createApp(fixtures, { fallthrough: false, redirect: true })
         })
 
         it('should 404 when directory', function (done) {
@@ -381,9 +381,9 @@ describe('express.static()', function () {
         })
       })
 
-      describe('with redirect: false', function () {
+      describe('with redirect: false', () => {
         before(function () {
-          this.app = createApp(fixtures, { 'fallthrough': false, 'redirect': false })
+          this.app = createApp(fixtures, { fallthrough: false, redirect: false })
         })
 
         it('should 404 when directory', function (done) {
@@ -401,9 +401,9 @@ describe('express.static()', function () {
     })
   })
 
-  describe('hidden files', function () {
+  describe('hidden files', () => {
     before(function () {
-      this.app = createApp(fixtures, { 'dotfiles': 'allow' })
+      this.app = createApp(fixtures, { dotfiles: 'allow' })
     })
 
     it('should be served when dotfiles: "allow" is given', function (done) {
@@ -415,33 +415,33 @@ describe('express.static()', function () {
     })
   })
 
-  describe('immutable', function () {
-    it('should default to false', function (done) {
+  describe('immutable', () => {
+    it('should default to false', (done) => {
       request(createApp(fixtures))
         .get('/nums.txt')
         .expect('Cache-Control', 'public, max-age=0', done)
     })
 
-    it('should set immutable directive in Cache-Control', function (done) {
-      request(createApp(fixtures, { 'immutable': true, 'maxAge': '1h' }))
+    it('should set immutable directive in Cache-Control', (done) => {
+      request(createApp(fixtures, { immutable: true, maxAge: '1h' }))
         .get('/nums.txt')
         .expect('Cache-Control', 'public, max-age=3600, immutable', done)
     })
   })
 
-  describe('lastModified', function () {
-    describe('when false', function () {
-      it('should not include Last-Modified', function (done) {
-        request(createApp(fixtures, { 'lastModified': false }))
+  describe('lastModified', () => {
+    describe('when false', () => {
+      it('should not include Last-Modified', (done) => {
+        request(createApp(fixtures, { lastModified: false }))
           .get('/nums.txt')
           .expect(utils.shouldNotHaveHeader('Last-Modified'))
           .expect(200, '123456789', done)
       })
     })
 
-    describe('when true', function () {
-      it('should include Last-Modified', function (done) {
-        request(createApp(fixtures, { 'lastModified': true }))
+    describe('when true', () => {
+      it('should include Last-Modified', (done) => {
+        request(createApp(fixtures, { lastModified: true }))
           .get('/nums.txt')
           .expect('Last-Modified', /^\w{3}, \d+ \w+ \d+ \d+:\d+:\d+ \w+$/)
           .expect(200, '123456789', done)
@@ -449,26 +449,26 @@ describe('express.static()', function () {
     })
   })
 
-  describe('maxAge', function () {
-    it('should accept string', function (done) {
-      request(createApp(fixtures, { 'maxAge': '30d' }))
+  describe('maxAge', () => {
+    it('should accept string', (done) => {
+      request(createApp(fixtures, { maxAge: '30d' }))
         .get('/todo.txt')
         .expect('cache-control', 'public, max-age=' + (60 * 60 * 24 * 30))
         .expect(200, done)
     })
 
-    it('should be reasonable when infinite', function (done) {
-      request(createApp(fixtures, { 'maxAge': Infinity }))
+    it('should be reasonable when infinite', (done) => {
+      request(createApp(fixtures, { maxAge: Infinity }))
         .get('/todo.txt')
         .expect('cache-control', 'public, max-age=' + (60 * 60 * 24 * 365))
         .expect(200, done)
     })
   })
 
-  describe('redirect', function () {
+  describe('redirect', () => {
     before(function () {
       this.app = express()
-      this.app.use(function (req, res, next) {
+      this.app.use((req, res, next) => {
         req.originalUrl = req.url =
           req.originalUrl.replace(/\/snow(\/|$)/, '/snow \u2603$1')
         next()
@@ -525,9 +525,9 @@ describe('express.static()', function () {
         .expect(404, done)
     })
 
-    describe('when false', function () {
+    describe('when false', () => {
       before(function () {
-        this.app = createApp(fixtures, { 'redirect': false })
+        this.app = createApp(fixtures, { redirect: false })
       })
 
       it('should disable redirect', function (done) {
@@ -538,16 +538,18 @@ describe('express.static()', function () {
     })
   })
 
-  describe('setHeaders', function () {
+  describe('setHeaders', () => {
     before(function () {
       this.app = express()
-      this.app.use(express.static(fixtures, { 'setHeaders': function (res) {
-        res.setHeader('x-custom', 'set')
-      } }))
+      this.app.use(express.static(fixtures, {
+        setHeaders: function (res) {
+          res.setHeader('x-custom', 'set')
+        }
+      }))
     })
 
-    it('should reject non-functions', function () {
-      assert.throws(express.static.bind(null, fixtures, { 'setHeaders': 3 }), /setHeaders.*function/)
+    it('should reject non-functions', () => {
+      assert.throws(express.static.bind(null, fixtures, { setHeaders: 3 }), /setHeaders.*function/)
     })
 
     it('should get called when sending file', function (done) {
@@ -572,9 +574,9 @@ describe('express.static()', function () {
     })
   })
 
-  describe('when traversing past root', function () {
+  describe('when traversing past root', () => {
     before(function () {
-      this.app = createApp(fixtures, { 'fallthrough': false })
+      this.app = createApp(fixtures, { fallthrough: false })
     })
 
     it('should catch urlencoded ../', function (done) {
@@ -590,7 +592,7 @@ describe('express.static()', function () {
     })
   })
 
-  describe('when request has "Range" header', function () {
+  describe('when request has "Range" header', () => {
     before(function () {
       this.app = createApp()
     })
@@ -645,7 +647,7 @@ describe('express.static()', function () {
         .expect(206, '34', done)
     })
 
-    describe('when last-byte-pos of the range is greater than current length', function () {
+    describe('when last-byte-pos of the range is greater than current length', () => {
       it('is taken to be equal to one less than the current length', function (done) {
         request(this.app)
           .get('/nums.txt')
@@ -662,7 +664,7 @@ describe('express.static()', function () {
       })
     })
 
-    describe('when the first- byte-pos of the range is greater than the current length', function () {
+    describe('when the first- byte-pos of the range is greater than the current length', () => {
       it('should respond with 416', function (done) {
         request(this.app)
           .get('/nums.txt')
@@ -679,7 +681,7 @@ describe('express.static()', function () {
       })
     })
 
-    describe('when syntactically invalid', function () {
+    describe('when syntactically invalid', () => {
       it('should respond with 200 and the entire contents', function (done) {
         request(this.app)
           .get('/nums.txt')
@@ -689,7 +691,7 @@ describe('express.static()', function () {
     })
   })
 
-  describe('when index at mount point', function () {
+  describe('when index at mount point', () => {
     before(function () {
       this.app = express()
       this.app.use('/users', express.static(fixtures + '/users'))
@@ -703,7 +705,7 @@ describe('express.static()', function () {
     })
   })
 
-  describe('when mounted', function () {
+  describe('when mounted', () => {
     before(function () {
       this.app = express()
       this.app.use('/static', express.static(fixtures))
@@ -729,7 +731,7 @@ describe('express.static()', function () {
   //       are doing, so this will prevent unseen
   //       regressions around this use-case.
   //
-  describe('when mounted "root" as a file', function () {
+  describe('when mounted "root" as a file', () => {
     before(function () {
       this.app = express()
       this.app.use('/todo.txt', express.static(fixtures + '/todo.txt'))
@@ -748,11 +750,11 @@ describe('express.static()', function () {
     })
   })
 
-  describe('when responding non-2xx or 304', function () {
-    it('should not alter the status', function (done) {
-      var app = express()
+  describe('when responding non-2xx or 304', () => {
+    it('should not alter the status', (done) => {
+      const app = express()
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         res.status(501)
         next()
       })
@@ -764,11 +766,11 @@ describe('express.static()', function () {
     })
   })
 
-  describe('when index file serving disabled', function () {
+  describe('when index file serving disabled', () => {
     before(function () {
       this.app = express()
-      this.app.use('/static', express.static(fixtures, { 'index': false }))
-      this.app.use(function (req, res, next) {
+      this.app.use('/static', express.static(fixtures, { index: false }))
+      this.app.use((req, res, next) => {
         res.sendStatus(404)
       })
     })
@@ -802,12 +804,12 @@ describe('express.static()', function () {
 })
 
 function createApp (dir, options, fn) {
-  var app = express()
-  var root = dir || fixtures
+  const app = express()
+  const root = dir || fixtures
 
   app.use(express.static(root, options))
 
-  app.use(function (req, res, next) {
+  app.use((req, res, next) => {
     res.sendStatus(404)
   })
 
diff --git a/test/express.text.js b/test/express.text.js
index e96cc5efe52..f6cb0d6b633 100644
--- a/test/express.text.js
+++ b/test/express.text.js
@@ -1,12 +1,12 @@
 'use strict'
 
-var assert = require('node:assert')
-var AsyncLocalStorage = require('node:async_hooks').AsyncLocalStorage
-const { Buffer } = require('node:buffer');
-var express = require('..')
-var request = require('supertest')
+const assert = require('node:assert')
+const { AsyncLocalStorage } = require('node:async_hooks')
+const { Buffer } = require('node:buffer')
+const express = require('../')
+const request = require('supertest')
 
-describe('express.text()', function () {
+describe('express.text()', () => {
   before(function () {
     this.app = createApp()
   })
@@ -19,17 +19,17 @@ describe('express.text()', function () {
       .expect(200, '"user is tobi"', done)
   })
 
-  it('should 400 when invalid content-length', function (done) {
-    var app = express()
+  it('should 400 when invalid content-length', (done) => {
+    const app = express()
 
-    app.use(function (req, res, next) {
+    app.use((req, res, next) => {
       req.headers['content-length'] = '20' // bad length
       next()
     })
 
     app.use(express.text())
 
-    app.post('/', function (req, res) {
+    app.post('/', (req, res) => {
       res.json(req.body)
     })
 
@@ -40,7 +40,7 @@ describe('express.text()', function () {
       .expect(400, /content length/, done)
   })
 
-  it('should handle Content-Length: 0', function (done) {
+  it('should handle Content-Length: 0', (done) => {
     request(createApp({ limit: '1kb' }))
       .post('/')
       .set('Content-Type', 'text/plain')
@@ -48,7 +48,7 @@ describe('express.text()', function () {
       .expect(200, '""', done)
   })
 
-  it('should handle empty message-body', function (done) {
+  it('should handle empty message-body', (done) => {
     request(createApp({ limit: '1kb' }))
       .post('/')
       .set('Content-Type', 'text/plain')
@@ -57,13 +57,13 @@ describe('express.text()', function () {
       .expect(200, '""', done)
   })
 
-  it('should handle duplicated middleware', function (done) {
-    var app = express()
+  it('should handle duplicated middleware', (done) => {
+    const app = express()
 
     app.use(express.text())
     app.use(express.text())
 
-    app.post('/', function (req, res) {
+    app.post('/', (req, res) => {
       res.json(req.body)
     })
 
@@ -74,27 +74,27 @@ describe('express.text()', function () {
       .expect(200, '"user is tobi"', done)
   })
 
-  describe('with defaultCharset option', function () {
-    it('should change default charset', function (done) {
-      var server = createApp({ defaultCharset: 'koi8-r' })
-      var test = request(server).post('/')
+  describe('with defaultCharset option', () => {
+    it('should change default charset', (done) => {
+      const server = createApp({ defaultCharset: 'koi8-r' })
+      const test = request(server).post('/')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('6e616d6520697320cec5d4', 'hex'))
       test.expect(200, '"name is нет"', done)
     })
 
-    it('should honor content-type charset', function (done) {
-      var server = createApp({ defaultCharset: 'koi8-r' })
-      var test = request(server).post('/')
+    it('should honor content-type charset', (done) => {
+      const server = createApp({ defaultCharset: 'koi8-r' })
+      const test = request(server).post('/')
       test.set('Content-Type', 'text/plain; charset=utf-8')
       test.write(Buffer.from('6e616d6520697320e8aeba', 'hex'))
       test.expect(200, '"name is 论"', done)
     })
   })
 
-  describe('with limit option', function () {
-    it('should 413 when over limit with Content-Length', function (done) {
-      var buf = Buffer.alloc(1028, '.')
+  describe('with limit option', () => {
+    it('should 413 when over limit with Content-Length', (done) => {
+      const buf = Buffer.alloc(1028, '.')
       request(createApp({ limit: '1kb' }))
         .post('/')
         .set('Content-Type', 'text/plain')
@@ -103,27 +103,27 @@ describe('express.text()', function () {
         .expect(413, done)
     })
 
-    it('should 413 when over limit with chunked encoding', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var buf = Buffer.alloc(1028, '.')
-      var test = request(app).post('/')
+    it('should 413 when over limit with chunked encoding', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const buf = Buffer.alloc(1028, '.')
+      const test = request(app).post('/')
       test.set('Content-Type', 'text/plain')
       test.set('Transfer-Encoding', 'chunked')
       test.write(buf.toString())
       test.expect(413, done)
     })
 
-    it('should 413 when inflated body over limit', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+    it('should 413 when inflated body over limit', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('1f8b080000000000000ad3d31b05a360148c64000087e5a14704040000', 'hex'))
       test.expect(413, done)
     })
 
-    it('should accept number of bytes', function (done) {
-      var buf = Buffer.alloc(1028, '.')
+    it('should accept number of bytes', (done) => {
+      const buf = Buffer.alloc(1028, '.')
       request(createApp({ limit: 1024 }))
         .post('/')
         .set('Content-Type', 'text/plain')
@@ -131,10 +131,10 @@ describe('express.text()', function () {
         .expect(413, done)
     })
 
-    it('should not change when options altered', function (done) {
-      var buf = Buffer.alloc(1028, '.')
-      var options = { limit: '1kb' }
-      var app = createApp(options)
+    it('should not change when options altered', (done) => {
+      const buf = Buffer.alloc(1028, '.')
+      const options = { limit: '1kb' }
+      const app = createApp(options)
 
       options.limit = '100kb'
 
@@ -145,10 +145,10 @@ describe('express.text()', function () {
         .expect(413, done)
     })
 
-    it('should not hang response', function (done) {
-      var app = createApp({ limit: '8kb' })
-      var buf = Buffer.alloc(10240, '.')
-      var test = request(app).post('/')
+    it('should not hang response', (done) => {
+      const app = createApp({ limit: '8kb' })
+      const buf = Buffer.alloc(10240, '.')
+      const test = request(app).post('/')
       test.set('Content-Type', 'text/plain')
       test.write(buf)
       test.write(buf)
@@ -156,26 +156,26 @@ describe('express.text()', function () {
       test.expect(413, done)
     })
 
-    it('should not error when inflating', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+    it('should not error when inflating', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('1f8b080000000000000ad3d31b05a360148c64000087e5a1470404', 'hex'))
-      setTimeout(function () {
+      setTimeout(() => {
         test.expect(413, done)
       }, 100)
     })
   })
 
-  describe('with inflate option', function () {
-    describe('when false', function () {
+  describe('with inflate option', () => {
+    describe('when false', () => {
       before(function () {
         this.app = createApp({ inflate: false })
       })
 
       it('should not accept content-encoding', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Encoding', 'gzip')
         test.set('Content-Type', 'text/plain')
         test.write(Buffer.from('1f8b080000000000000bcb4bcc4d55c82c5678b16e170072b3e0200b000000', 'hex'))
@@ -183,13 +183,13 @@ describe('express.text()', function () {
       })
     })
 
-    describe('when true', function () {
+    describe('when true', () => {
       before(function () {
         this.app = createApp({ inflate: true })
       })
 
       it('should accept content-encoding', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Encoding', 'gzip')
         test.set('Content-Type', 'text/plain')
         test.write(Buffer.from('1f8b080000000000000bcb4bcc4d55c82c5678b16e170072b3e0200b000000', 'hex'))
@@ -198,8 +198,8 @@ describe('express.text()', function () {
     })
   })
 
-  describe('with type option', function () {
-    describe('when "text/html"', function () {
+  describe('with type option', () => {
+    describe('when "text/html"', () => {
       before(function () {
         this.app = createApp({ type: 'text/html' })
       })
@@ -221,7 +221,7 @@ describe('express.text()', function () {
       })
     })
 
-    describe('when ["text/html", "text/plain"]', function () {
+    describe('when ["text/html", "text/plain"]', () => {
       before(function () {
         this.app = createApp({ type: ['text/html', 'text/plain'] })
       })
@@ -251,9 +251,9 @@ describe('express.text()', function () {
       })
     })
 
-    describe('when a function', function () {
-      it('should parse when truthy value returned', function (done) {
-        var app = createApp({ type: accept })
+    describe('when a function', () => {
+      it('should parse when truthy value returned', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           return req.headers['content-type'] === 'text/vnd.something'
@@ -266,20 +266,20 @@ describe('express.text()', function () {
           .expect(200, '"user is tobi"', done)
       })
 
-      it('should work without content-type', function (done) {
-        var app = createApp({ type: accept })
+      it('should work without content-type', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           return true
         }
 
-        var test = request(app).post('/')
+        const test = request(app).post('/')
         test.write('user is tobi')
         test.expect(200, '"user is tobi"', done)
       })
 
-      it('should not invoke without a body', function (done) {
-        var app = createApp({ type: accept })
+      it('should not invoke without a body', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           throw new Error('oops!')
@@ -292,14 +292,14 @@ describe('express.text()', function () {
     })
   })
 
-  describe('with verify option', function () {
-    it('should assert value is function', function () {
+  describe('with verify option', () => {
+    it('should assert value is function', () => {
       assert.throws(createApp.bind(null, { verify: 'lol' }),
         /TypeError: option verify must be function/)
     })
 
-    it('should error from verify', function (done) {
-      var app = createApp({
+    it('should error from verify', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x20) throw new Error('no leading space')
         }
@@ -312,11 +312,11 @@ describe('express.text()', function () {
         .expect(403, '[entity.verify.failed] no leading space', done)
     })
 
-    it('should allow custom codes', function (done) {
-      var app = createApp({
+    it('should allow custom codes', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] !== 0x20) return
-          var err = new Error('no leading space')
+          const err = new Error('no leading space')
           err.status = 400
           throw err
         }
@@ -329,8 +329,8 @@ describe('express.text()', function () {
         .expect(400, '[entity.verify.failed] no leading space', done)
     })
 
-    it('should allow pass-through', function (done) {
-      var app = createApp({
+    it('should allow pass-through', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x20) throw new Error('no leading space')
         }
@@ -343,34 +343,34 @@ describe('express.text()', function () {
         .expect(200, '"user is tobi"', done)
     })
 
-    it('should 415 on unknown charset prior to verify', function (done) {
-      var app = createApp({
+    it('should 415 on unknown charset prior to verify', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           throw new Error('unexpected verify call')
         }
       })
 
-      var test = request(app).post('/')
+      const test = request(app).post('/')
       test.set('Content-Type', 'text/plain; charset=x-bogus')
       test.write(Buffer.from('00000000', 'hex'))
       test.expect(415, '[charset.unsupported] unsupported charset "X-BOGUS"', done)
     })
   })
 
-  describe('async local storage', function () {
+  describe('async local storage', () => {
     before(function () {
-      var app = express()
-      var store = { foo: 'bar' }
+      const app = express()
+      const store = { foo: 'bar' }
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         req.asyncLocalStorage = new AsyncLocalStorage()
         req.asyncLocalStorage.run(store, next)
       })
 
       app.use(express.text())
 
-      app.use(function (req, res, next) {
-        var local = req.asyncLocalStorage.getStore()
+      app.use((req, res, next) => {
+        const local = req.asyncLocalStorage.getStore()
 
         if (local) {
           res.setHeader('x-store-foo', String(local.foo))
@@ -379,8 +379,8 @@ describe('express.text()', function () {
         next()
       })
 
-      app.use(function (err, req, res, next) {
-        var local = req.asyncLocalStorage.getStore()
+      app.use((err, req, res, next) => {
+        const local = req.asyncLocalStorage.getStore()
 
         if (local) {
           res.setHeader('x-store-foo', String(local.foo))
@@ -390,7 +390,7 @@ describe('express.text()', function () {
         res.send('[' + err.type + '] ' + err.message)
       })
 
-      app.post('/', function (req, res) {
+      app.post('/', (req, res) => {
         res.json(req.body)
       })
 
@@ -419,7 +419,7 @@ describe('express.text()', function () {
     })
 
     it('should persist store when inflated', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4d55c82c5678b16e170072b3e0200b000000', 'hex'))
@@ -430,7 +430,7 @@ describe('express.text()', function () {
     })
 
     it('should persist store when inflate error', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4d55c82c5678b16e170072b3e0200b0000', 'hex'))
@@ -450,27 +450,27 @@ describe('express.text()', function () {
     })
   })
 
-  describe('charset', function () {
+  describe('charset', () => {
     before(function () {
       this.app = createApp()
     })
 
     it('should parse utf-8', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'text/plain; charset=utf-8')
       test.write(Buffer.from('6e616d6520697320e8aeba', 'hex'))
       test.expect(200, '"name is 论"', done)
     })
 
     it('should parse codepage charsets', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'text/plain; charset=koi8-r')
       test.write(Buffer.from('6e616d6520697320cec5d4', 'hex'))
       test.expect(200, '"name is нет"', done)
     })
 
     it('should parse when content-length != char length', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'text/plain; charset=utf-8')
       test.set('Content-Length', '11')
       test.write(Buffer.from('6e616d6520697320e8aeba', 'hex'))
@@ -478,34 +478,34 @@ describe('express.text()', function () {
     })
 
     it('should default to utf-8', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('6e616d6520697320e8aeba', 'hex'))
       test.expect(200, '"name is 论"', done)
     })
 
     it('should 415 on unknown charset', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'text/plain; charset=x-bogus')
       test.write(Buffer.from('00000000', 'hex'))
       test.expect(415, '[charset.unsupported] unsupported charset "X-BOGUS"', done)
     })
   })
 
-  describe('encoding', function () {
+  describe('encoding', () => {
     before(function () {
       this.app = createApp({ limit: '10kb' })
     })
 
     it('should parse without encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('6e616d6520697320e8aeba', 'hex'))
       test.expect(200, '"name is 论"', done)
     })
 
     it('should support identity encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'identity')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('6e616d6520697320e8aeba', 'hex'))
@@ -513,7 +513,7 @@ describe('express.text()', function () {
     })
 
     it('should support gzip encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4d55c82c5678b16e170072b3e0200b000000', 'hex'))
@@ -521,7 +521,7 @@ describe('express.text()', function () {
     })
 
     it('should support deflate encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'deflate')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('789ccb4bcc4d55c82c5678b16e17001a6f050e', 'hex'))
@@ -529,7 +529,7 @@ describe('express.text()', function () {
     })
 
     it('should be case-insensitive', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'GZIP')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4d55c82c5678b16e170072b3e0200b000000', 'hex'))
@@ -537,7 +537,7 @@ describe('express.text()', function () {
     })
 
     it('should 415 on unknown encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'nulls')
       test.set('Content-Type', 'text/plain')
       test.write(Buffer.from('000000000000', 'hex'))
@@ -547,18 +547,18 @@ describe('express.text()', function () {
 })
 
 function createApp (options) {
-  var app = express()
+  const app = express()
 
   app.use(express.text(options))
 
-  app.use(function (err, req, res, next) {
+  app.use((err, req, res, next) => {
     res.status(err.status || 500)
     res.send(String(req.headers['x-error-property']
       ? err[req.headers['x-error-property']]
       : ('[' + err.type + '] ' + err.message)))
   })
 
-  app.post('/', function (req, res) {
+  app.post('/', (req, res) => {
     res.json(req.body)
   })
 
diff --git a/test/express.urlencoded.js b/test/express.urlencoded.js
index f4acf231989..bd9559bb91e 100644
--- a/test/express.urlencoded.js
+++ b/test/express.urlencoded.js
@@ -1,13 +1,13 @@
 'use strict'
 
-var assert = require('node:assert')
-var AsyncLocalStorage = require('node:async_hooks').AsyncLocalStorage
-const { Buffer } = require('node:buffer');
+const assert = require('node:assert')
+const { AsyncLocalStorage } = require('node:async_hooks')
+const { Buffer } = require('node:buffer')
 
-var express = require('..')
-var request = require('supertest')
+const express = require('../')
+const request = require('supertest')
 
-describe('express.urlencoded()', function () {
+describe('express.urlencoded()', () => {
   before(function () {
     this.app = createApp()
   })
@@ -20,17 +20,17 @@ describe('express.urlencoded()', function () {
       .expect(200, '{"user":"tobi"}', done)
   })
 
-  it('should 400 when invalid content-length', function (done) {
-    var app = express()
+  it('should 400 when invalid content-length', (done) => {
+    const app = express()
 
-    app.use(function (req, res, next) {
+    app.use((req, res, next) => {
       req.headers['content-length'] = '20' // bad length
       next()
     })
 
     app.use(express.urlencoded())
 
-    app.post('/', function (req, res) {
+    app.post('/', (req, res) => {
       res.json(req.body)
     })
 
@@ -50,7 +50,7 @@ describe('express.urlencoded()', function () {
       .expect(200, '{}', done)
   })
 
-  it('should handle empty message-body', function (done) {
+  it('should handle empty message-body', (done) => {
     request(createApp({ limit: '1kb' }))
       .post('/')
       .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -59,13 +59,13 @@ describe('express.urlencoded()', function () {
       .expect(200, '{}', done)
   })
 
-  it('should handle duplicated middleware', function (done) {
-    var app = express()
+  it('should handle duplicated middleware', (done) => {
+    const app = express()
 
     app.use(express.urlencoded())
     app.use(express.urlencoded())
 
-    app.post('/', function (req, res) {
+    app.post('/', (req, res) => {
       res.json(req.body)
     })
 
@@ -84,8 +84,8 @@ describe('express.urlencoded()', function () {
       .expect(200, '{"user[name][first]":"Tobi"}', done)
   })
 
-  describe('with extended option', function () {
-    describe('when false', function () {
+  describe('with extended option', () => {
+    describe('when false', () => {
       before(function () {
         this.app = createApp({ extended: false })
       })
@@ -107,7 +107,7 @@ describe('express.urlencoded()', function () {
       })
     })
 
-    describe('when true', function () {
+    describe('when true', () => {
       before(function () {
         this.app = createApp({ extended: true })
       })
@@ -153,9 +153,9 @@ describe('express.urlencoded()', function () {
       })
 
       it('should parse array index notation with large array', function (done) {
-        var str = 'f[0]=0'
+        let str = 'f[0]=0'
 
-        for (var i = 1; i < 500; i++) {
+        for (let i = 1; i < 500; i++) {
           str += '&f[' + i + ']=' + i.toString(16)
         }
 
@@ -163,8 +163,8 @@ describe('express.urlencoded()', function () {
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
           .send(str)
-          .expect(function (res) {
-            var obj = JSON.parse(res.text)
+          .expect((res) => {
+            const obj = JSON.parse(res.text)
             assert.strictEqual(Object.keys(obj).length, 1)
             assert.strictEqual(Array.isArray(obj.f), true)
             assert.strictEqual(obj.f.length, 500)
@@ -181,9 +181,9 @@ describe('express.urlencoded()', function () {
       })
 
       it('should parse deep object', function (done) {
-        var str = 'foo'
+        let str = 'foo'
 
-        for (var i = 0; i < 32; i++) {
+        for (let i = 0; i < 32; i++) {
           str += '[p]'
         }
 
@@ -193,13 +193,13 @@ describe('express.urlencoded()', function () {
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
           .send(str)
-          .expect(function (res) {
-            var obj = JSON.parse(res.text)
+          .expect((res) => {
+            const obj = JSON.parse(res.text)
             assert.strictEqual(Object.keys(obj).length, 1)
             assert.strictEqual(typeof obj.foo, 'object')
 
-            var depth = 0
-            var ref = obj.foo
+            let depth = 0
+            let ref = obj.foo
             while ((ref = ref.p)) { depth++ }
             assert.strictEqual(depth, 32)
           })
@@ -208,14 +208,14 @@ describe('express.urlencoded()', function () {
     })
   })
 
-  describe('with inflate option', function () {
-    describe('when false', function () {
+  describe('with inflate option', () => {
+    describe('when false', () => {
       before(function () {
         this.app = createApp({ inflate: false })
       })
 
       it('should not accept content-encoding', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Encoding', 'gzip')
         test.set('Content-Type', 'application/x-www-form-urlencoded')
         test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -223,13 +223,13 @@ describe('express.urlencoded()', function () {
       })
     })
 
-    describe('when true', function () {
+    describe('when true', () => {
       before(function () {
         this.app = createApp({ inflate: true })
       })
 
       it('should accept content-encoding', function (done) {
-        var test = request(this.app).post('/')
+        const test = request(this.app).post('/')
         test.set('Content-Encoding', 'gzip')
         test.set('Content-Type', 'application/x-www-form-urlencoded')
         test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -238,9 +238,9 @@ describe('express.urlencoded()', function () {
     })
   })
 
-  describe('with limit option', function () {
-    it('should 413 when over limit with Content-Length', function (done) {
-      var buf = Buffer.alloc(1024, '.')
+  describe('with limit option', () => {
+    it('should 413 when over limit with Content-Length', (done) => {
+      const buf = Buffer.alloc(1024, '.')
       request(createApp({ limit: '1kb' }))
         .post('/')
         .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -249,10 +249,10 @@ describe('express.urlencoded()', function () {
         .expect(413, done)
     })
 
-    it('should 413 when over limit with chunked encoding', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var buf = Buffer.alloc(1024, '.')
-      var test = request(app).post('/')
+    it('should 413 when over limit with chunked encoding', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const buf = Buffer.alloc(1024, '.')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.set('Transfer-Encoding', 'chunked')
       test.write('str=')
@@ -260,17 +260,17 @@ describe('express.urlencoded()', function () {
       test.expect(413, done)
     })
 
-    it('should 413 when inflated body over limit', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+    it('should 413 when inflated body over limit', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('1f8b080000000000000a2b2e29b2d51b05a360148c580000a0351f9204040000', 'hex'))
       test.expect(413, done)
     })
 
-    it('should accept number of bytes', function (done) {
-      var buf = Buffer.alloc(1024, '.')
+    it('should accept number of bytes', (done) => {
+      const buf = Buffer.alloc(1024, '.')
       request(createApp({ limit: 1024 }))
         .post('/')
         .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -278,10 +278,10 @@ describe('express.urlencoded()', function () {
         .expect(413, done)
     })
 
-    it('should not change when options altered', function (done) {
-      var buf = Buffer.alloc(1024, '.')
-      var options = { limit: '1kb' }
-      var app = createApp(options)
+    it('should not change when options altered', (done) => {
+      const buf = Buffer.alloc(1024, '.')
+      const options = { limit: '1kb' }
+      const app = createApp(options)
 
       options.limit = '100kb'
 
@@ -292,10 +292,10 @@ describe('express.urlencoded()', function () {
         .expect(413, done)
     })
 
-    it('should not hang response', function (done) {
-      var app = createApp({ limit: '8kb' })
-      var buf = Buffer.alloc(10240, '.')
-      var test = request(app).post('/')
+    it('should not hang response', (done) => {
+      const app = createApp({ limit: '8kb' })
+      const buf = Buffer.alloc(10240, '.')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(buf)
       test.write(buf)
@@ -303,9 +303,9 @@ describe('express.urlencoded()', function () {
       test.expect(413, done)
     })
 
-    it('should not error when inflating', function (done) {
-      var app = createApp({ limit: '1kb' })
-      var test = request(app).post('/')
+    it('should not error when inflating', (done) => {
+      const app = createApp({ limit: '1kb' })
+      const test = request(app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('1f8b080000000000000a2b2e29b2d51b05a360148c580000a0351f92040400', 'hex'))
@@ -313,19 +313,19 @@ describe('express.urlencoded()', function () {
     })
   })
 
-  describe('with parameterLimit option', function () {
-    describe('with extended: false', function () {
-      it('should reject 0', function () {
+  describe('with parameterLimit option', () => {
+    describe('with extended: false', () => {
+      it('should reject 0', () => {
         assert.throws(createApp.bind(null, { extended: false, parameterLimit: 0 }),
           /TypeError: option parameterLimit must be a positive number/)
       })
 
-      it('should reject string', function () {
+      it('should reject string', () => {
         assert.throws(createApp.bind(null, { extended: false, parameterLimit: 'beep' }),
           /TypeError: option parameterLimit must be a positive number/)
       })
 
-      it('should 413 if over limit', function (done) {
+      it('should 413 if over limit', (done) => {
         request(createApp({ extended: false, parameterLimit: 10 }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -333,7 +333,7 @@ describe('express.urlencoded()', function () {
           .expect(413, '[parameters.too.many] too many parameters', done)
       })
 
-      it('should work when at the limit', function (done) {
+      it('should work when at the limit', (done) => {
         request(createApp({ extended: false, parameterLimit: 10 }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -342,7 +342,7 @@ describe('express.urlencoded()', function () {
           .expect(200, done)
       })
 
-      it('should work if number is floating point', function (done) {
+      it('should work if number is floating point', (done) => {
         request(createApp({ extended: false, parameterLimit: 10.1 }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -350,7 +350,7 @@ describe('express.urlencoded()', function () {
           .expect(413, /too many parameters/, done)
       })
 
-      it('should work with large limit', function (done) {
+      it('should work with large limit', (done) => {
         request(createApp({ extended: false, parameterLimit: 5000 }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -359,7 +359,7 @@ describe('express.urlencoded()', function () {
           .expect(200, done)
       })
 
-      it('should work with Infinity limit', function (done) {
+      it('should work with Infinity limit', (done) => {
         request(createApp({ extended: false, parameterLimit: Infinity }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -369,18 +369,18 @@ describe('express.urlencoded()', function () {
       })
     })
 
-    describe('with extended: true', function () {
-      it('should reject 0', function () {
+    describe('with extended: true', () => {
+      it('should reject 0', () => {
         assert.throws(createApp.bind(null, { extended: true, parameterLimit: 0 }),
           /TypeError: option parameterLimit must be a positive number/)
       })
 
-      it('should reject string', function () {
+      it('should reject string', () => {
         assert.throws(createApp.bind(null, { extended: true, parameterLimit: 'beep' }),
           /TypeError: option parameterLimit must be a positive number/)
       })
 
-      it('should 413 if over limit', function (done) {
+      it('should 413 if over limit', (done) => {
         request(createApp({ extended: true, parameterLimit: 10 }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -388,7 +388,7 @@ describe('express.urlencoded()', function () {
           .expect(413, '[parameters.too.many] too many parameters', done)
       })
 
-      it('should work when at the limit', function (done) {
+      it('should work when at the limit', (done) => {
         request(createApp({ extended: true, parameterLimit: 10 }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -397,7 +397,7 @@ describe('express.urlencoded()', function () {
           .expect(200, done)
       })
 
-      it('should work if number is floating point', function (done) {
+      it('should work if number is floating point', (done) => {
         request(createApp({ extended: true, parameterLimit: 10.1 }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -405,7 +405,7 @@ describe('express.urlencoded()', function () {
           .expect(413, /too many parameters/, done)
       })
 
-      it('should work with large limit', function (done) {
+      it('should work with large limit', (done) => {
         request(createApp({ extended: true, parameterLimit: 5000 }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -414,7 +414,7 @@ describe('express.urlencoded()', function () {
           .expect(200, done)
       })
 
-      it('should work with Infinity limit', function (done) {
+      it('should work with Infinity limit', (done) => {
         request(createApp({ extended: true, parameterLimit: Infinity }))
           .post('/')
           .set('Content-Type', 'application/x-www-form-urlencoded')
@@ -425,8 +425,8 @@ describe('express.urlencoded()', function () {
     })
   })
 
-  describe('with type option', function () {
-    describe('when "application/vnd.x-www-form-urlencoded"', function () {
+  describe('with type option', () => {
+    describe('when "application/vnd.x-www-form-urlencoded"', () => {
       before(function () {
         this.app = createApp({ type: 'application/vnd.x-www-form-urlencoded' })
       })
@@ -448,7 +448,7 @@ describe('express.urlencoded()', function () {
       })
     })
 
-    describe('when ["urlencoded", "application/x-pairs"]', function () {
+    describe('when ["urlencoded", "application/x-pairs"]', () => {
       before(function () {
         this.app = createApp({
           type: ['urlencoded', 'application/x-pairs']
@@ -480,9 +480,9 @@ describe('express.urlencoded()', function () {
       })
     })
 
-    describe('when a function', function () {
-      it('should parse when truthy value returned', function (done) {
-        var app = createApp({ type: accept })
+    describe('when a function', () => {
+      it('should parse when truthy value returned', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           return req.headers['content-type'] === 'application/vnd.something'
@@ -495,20 +495,20 @@ describe('express.urlencoded()', function () {
           .expect(200, '{"user":"tobi"}', done)
       })
 
-      it('should work without content-type', function (done) {
-        var app = createApp({ type: accept })
+      it('should work without content-type', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           return true
         }
 
-        var test = request(app).post('/')
+        const test = request(app).post('/')
         test.write('user=tobi')
         test.expect(200, '{"user":"tobi"}', done)
       })
 
-      it('should not invoke without a body', function (done) {
-        var app = createApp({ type: accept })
+      it('should not invoke without a body', (done) => {
+        const app = createApp({ type: accept })
 
         function accept (req) {
           throw new Error('oops!')
@@ -521,14 +521,14 @@ describe('express.urlencoded()', function () {
     })
   })
 
-  describe('with verify option', function () {
-    it('should assert value if function', function () {
+  describe('with verify option', () => {
+    it('should assert value if function', () => {
       assert.throws(createApp.bind(null, { verify: 'lol' }),
         /TypeError: option verify must be function/)
     })
 
-    it('should error from verify', function (done) {
-      var app = createApp({
+    it('should error from verify', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x20) throw new Error('no leading space')
         }
@@ -541,11 +541,11 @@ describe('express.urlencoded()', function () {
         .expect(403, '[entity.verify.failed] no leading space', done)
     })
 
-    it('should allow custom codes', function (done) {
-      var app = createApp({
+    it('should allow custom codes', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] !== 0x20) return
-          var err = new Error('no leading space')
+          const err = new Error('no leading space')
           err.status = 400
           throw err
         }
@@ -558,11 +558,11 @@ describe('express.urlencoded()', function () {
         .expect(400, '[entity.verify.failed] no leading space', done)
     })
 
-    it('should allow custom type', function (done) {
-      var app = createApp({
+    it('should allow custom type', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] !== 0x20) return
-          var err = new Error('no leading space')
+          const err = new Error('no leading space')
           err.type = 'foo.bar'
           throw err
         }
@@ -575,8 +575,8 @@ describe('express.urlencoded()', function () {
         .expect(403, '[foo.bar] no leading space', done)
     })
 
-    it('should allow pass-through', function (done) {
-      var app = createApp({
+    it('should allow pass-through', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           if (buf[0] === 0x5b) throw new Error('no arrays')
         }
@@ -589,34 +589,34 @@ describe('express.urlencoded()', function () {
         .expect(200, '{"user":"tobi"}', done)
     })
 
-    it('should 415 on unknown charset prior to verify', function (done) {
-      var app = createApp({
+    it('should 415 on unknown charset prior to verify', (done) => {
+      const app = createApp({
         verify: function (req, res, buf) {
           throw new Error('unexpected verify call')
         }
       })
 
-      var test = request(app).post('/')
+      const test = request(app).post('/')
       test.set('Content-Type', 'application/x-www-form-urlencoded; charset=x-bogus')
       test.write(Buffer.from('00000000', 'hex'))
       test.expect(415, '[charset.unsupported] unsupported charset "X-BOGUS"', done)
     })
   })
 
-  describe('async local storage', function () {
+  describe('async local storage', () => {
     before(function () {
-      var app = express()
-      var store = { foo: 'bar' }
+      const app = express()
+      const store = { foo: 'bar' }
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         req.asyncLocalStorage = new AsyncLocalStorage()
         req.asyncLocalStorage.run(store, next)
       })
 
       app.use(express.urlencoded())
 
-      app.use(function (req, res, next) {
-        var local = req.asyncLocalStorage.getStore()
+      app.use((req, res, next) => {
+        const local = req.asyncLocalStorage.getStore()
 
         if (local) {
           res.setHeader('x-store-foo', String(local.foo))
@@ -625,8 +625,8 @@ describe('express.urlencoded()', function () {
         next()
       })
 
-      app.use(function (err, req, res, next) {
-        var local = req.asyncLocalStorage.getStore()
+      app.use((err, req, res, next) => {
+        const local = req.asyncLocalStorage.getStore()
 
         if (local) {
           res.setHeader('x-store-foo', String(local.foo))
@@ -636,7 +636,7 @@ describe('express.urlencoded()', function () {
         res.send('[' + err.type + '] ' + err.message)
       })
 
-      app.post('/', function (req, res) {
+      app.post('/', (req, res) => {
         res.json(req.body)
       })
 
@@ -665,7 +665,7 @@ describe('express.urlencoded()', function () {
     })
 
     it('should persist store when inflated', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -676,7 +676,7 @@ describe('express.urlencoded()', function () {
     })
 
     it('should persist store when inflate error', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad6080000', 'hex'))
@@ -696,20 +696,20 @@ describe('express.urlencoded()', function () {
     })
   })
 
-  describe('charset', function () {
+  describe('charset', () => {
     before(function () {
       this.app = createApp()
     })
 
     it('should parse utf-8', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/x-www-form-urlencoded; charset=utf-8')
       test.write(Buffer.from('6e616d653de8aeba', 'hex'))
       test.expect(200, '{"name":"论"}', done)
     })
 
     it('should parse when content-length != char length', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/x-www-form-urlencoded; charset=utf-8')
       test.set('Content-Length', '7')
       test.write(Buffer.from('746573743dc3a5', 'hex'))
@@ -717,34 +717,34 @@ describe('express.urlencoded()', function () {
     })
 
     it('should default to utf-8', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('6e616d653de8aeba', 'hex'))
       test.expect(200, '{"name":"论"}', done)
     })
 
     it('should fail on unknown charset', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/x-www-form-urlencoded; charset=koi8-r')
       test.write(Buffer.from('6e616d653dcec5d4', 'hex'))
       test.expect(415, '[charset.unsupported] unsupported charset "KOI8-R"', done)
     })
   })
 
-  describe('encoding', function () {
+  describe('encoding', () => {
     before(function () {
       this.app = createApp({ limit: '10kb' })
     })
 
     it('should parse without encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('6e616d653de8aeba', 'hex'))
       test.expect(200, '{"name":"论"}', done)
     })
 
     it('should support identity encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'identity')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('6e616d653de8aeba', 'hex'))
@@ -752,7 +752,7 @@ describe('express.urlencoded()', function () {
     })
 
     it('should support gzip encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'gzip')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -760,7 +760,7 @@ describe('express.urlencoded()', function () {
     })
 
     it('should support deflate encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'deflate')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('789ccb4bcc4db57db16e17001068042f', 'hex'))
@@ -768,7 +768,7 @@ describe('express.urlencoded()', function () {
     })
 
     it('should be case-insensitive', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'GZIP')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('1f8b080000000000000bcb4bcc4db57db16e170099a4bad608000000', 'hex'))
@@ -776,7 +776,7 @@ describe('express.urlencoded()', function () {
     })
 
     it('should 415 on unknown encoding', function (done) {
-      var test = request(this.app).post('/')
+      const test = request(this.app).post('/')
       test.set('Content-Encoding', 'nulls')
       test.set('Content-Type', 'application/x-www-form-urlencoded')
       test.write(Buffer.from('000000000000', 'hex'))
@@ -786,7 +786,7 @@ describe('express.urlencoded()', function () {
 })
 
 function createManyParams (count) {
-  var str = ''
+  let str = ''
 
   if (count === 0) {
     return str
@@ -794,8 +794,8 @@ function createManyParams (count) {
 
   str += '0=0'
 
-  for (var i = 1; i < count; i++) {
-    var n = i.toString(36)
+  for (let i = 1; i < count; i++) {
+    const n = i.toString(36)
     str += '&' + n + '=' + n
   }
 
@@ -803,18 +803,18 @@ function createManyParams (count) {
 }
 
 function createApp (options) {
-  var app = express()
+  const app = express()
 
   app.use(express.urlencoded(options))
 
-  app.use(function (err, req, res, next) {
+  app.use((err, req, res, next) => {
     res.status(err.status || 500)
     res.send(String(req.headers['x-error-property']
       ? err[req.headers['x-error-property']]
       : ('[' + err.type + '] ' + err.message)))
   })
 
-  app.post('/', function (req, res) {
+  app.post('/', (req, res) => {
     res.json(req.body)
   })
 
diff --git a/test/middleware.basic.js b/test/middleware.basic.js
index 1f1ed17571a..2270909d247 100644
--- a/test/middleware.basic.js
+++ b/test/middleware.basic.js
@@ -1,42 +1,42 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('../');
-var request = require('supertest');
+const assert = require('node:assert')
+const express = require('../')
+const request = require('supertest')
 
-describe('middleware', function(){
-  describe('.next()', function(){
-    it('should behave like connect', function(done){
-      var app = express()
-        , calls = [];
+describe('middleware', () => {
+  describe('.next()', () => {
+    it('should behave like connect', (done) => {
+      const app = express()
+      const calls = []
 
-      app.use(function(req, res, next){
-        calls.push('one');
-        next();
-      });
+      app.use((req, res, next) => {
+        calls.push('one')
+        next()
+      })
 
-      app.use(function(req, res, next){
-        calls.push('two');
-        next();
-      });
+      app.use((req, res, next) => {
+        calls.push('two')
+        next()
+      })
 
-      app.use(function(req, res){
-        var buf = '';
-        res.setHeader('Content-Type', 'application/json');
-        req.setEncoding('utf8');
-        req.on('data', function(chunk){ buf += chunk });
-        req.on('end', function(){
-          res.end(buf);
-        });
-      });
+      app.use((req, res) => {
+        let buf = ''
+        res.setHeader('Content-Type', 'application/json')
+        req.setEncoding('utf8')
+        req.on('data', (chunk) => { buf += chunk })
+        req.on('end', () => {
+          res.end(buf)
+        })
+      })
 
       request(app)
-      .get('/')
-      .set('Content-Type', 'application/json')
-      .send('{"foo":"bar"}')
-      .expect('Content-Type', 'application/json')
-      .expect(function () { assert.deepEqual(calls, ['one', 'two']) })
-      .expect(200, '{"foo":"bar"}', done)
+        .get('/')
+        .set('Content-Type', 'application/json')
+        .send('{"foo":"bar"}')
+        .expect('Content-Type', 'application/json')
+        .expect(() => { assert.deepEqual(calls, ['one', 'two']) })
+        .expect(200, '{"foo":"bar"}', done)
     })
   })
 })
diff --git a/test/regression.js b/test/regression.js
index 4e99b306948..c53173d2ed4 100644
--- a/test/regression.js
+++ b/test/regression.js
@@ -1,20 +1,20 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('throw after .end()', function(){
-  it('should fail gracefully', function(done){
-    var app = express();
+describe('throw after .end()', () => {
+  it('should fail gracefully', (done) => {
+    const app = express()
 
-    app.get('/', function(req, res){
-      res.end('yay');
-      throw new Error('boom');
-    });
+    app.get('/', (req, res) => {
+      res.end('yay')
+      throw new Error('boom')
+    })
 
     request(app)
-    .get('/')
-    .expect('yay')
-    .expect(200, done);
+      .get('/')
+      .expect('yay')
+      .expect(200, done)
   })
 })
diff --git a/test/req.accepts.js b/test/req.accepts.js
index 2066fb51859..c941d8a3867 100644
--- a/test/req.accepts.js
+++ b/test/req.accepts.js
@@ -1,125 +1,125 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.accepts(type)', function(){
-    it('should return true when Accept is not present', function(done){
-      var app = express();
+describe('req', () => {
+  describe('.accepts(type)', () => {
+    it('should return true when Accept is not present', (done) => {
+      const app = express()
 
-      app.use(function(req, res, next){
-        res.end(req.accepts('json') ? 'yes' : 'no');
-      });
+      app.use((req, res, next) => {
+        res.end(req.accepts('json') ? 'yes' : 'no')
+      })
 
       request(app)
-      .get('/')
-      .expect('yes', done);
+        .get('/')
+        .expect('yes', done)
     })
 
-    it('should return true when present', function(done){
-      var app = express();
+    it('should return true when present', (done) => {
+      const app = express()
 
-      app.use(function(req, res, next){
-        res.end(req.accepts('json') ? 'yes' : 'no');
-      });
+      app.use((req, res, next) => {
+        res.end(req.accepts('json') ? 'yes' : 'no')
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', 'application/json')
-      .expect('yes', done);
+        .get('/')
+        .set('Accept', 'application/json')
+        .expect('yes', done)
     })
 
-    it('should return false otherwise', function(done){
-      var app = express();
+    it('should return false otherwise', (done) => {
+      const app = express()
 
-      app.use(function(req, res, next){
-        res.end(req.accepts('json') ? 'yes' : 'no');
-      });
+      app.use((req, res, next) => {
+        res.end(req.accepts('json') ? 'yes' : 'no')
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', 'text/html')
-      .expect('no', done);
+        .get('/')
+        .set('Accept', 'text/html')
+        .expect('no', done)
     })
   })
 
-  it('should accept an argument list of type names', function(done){
-    var app = express();
+  it('should accept an argument list of type names', (done) => {
+    const app = express()
 
-    app.use(function(req, res, next){
-      res.end(req.accepts('json', 'html'));
-    });
+    app.use((req, res, next) => {
+      res.end(req.accepts('json', 'html'))
+    })
 
     request(app)
-    .get('/')
-    .set('Accept', 'application/json')
-    .expect('json', done);
+      .get('/')
+      .set('Accept', 'application/json')
+      .expect('json', done)
   })
 
-  describe('.accepts(types)', function(){
-    it('should return the first when Accept is not present', function(done){
-      var app = express();
+  describe('.accepts(types)', () => {
+    it('should return the first when Accept is not present', (done) => {
+      const app = express()
 
-      app.use(function(req, res, next){
-        res.end(req.accepts(['json', 'html']));
-      });
+      app.use((req, res, next) => {
+        res.end(req.accepts(['json', 'html']))
+      })
 
       request(app)
-      .get('/')
-      .expect('json', done);
+        .get('/')
+        .expect('json', done)
     })
 
-    it('should return the first acceptable type', function(done){
-      var app = express();
+    it('should return the first acceptable type', (done) => {
+      const app = express()
 
-      app.use(function(req, res, next){
-        res.end(req.accepts(['json', 'html']));
-      });
+      app.use((req, res, next) => {
+        res.end(req.accepts(['json', 'html']))
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', 'text/html')
-      .expect('html', done);
+        .get('/')
+        .set('Accept', 'text/html')
+        .expect('html', done)
     })
 
-    it('should return false when no match is made', function(done){
-      var app = express();
+    it('should return false when no match is made', (done) => {
+      const app = express()
 
-      app.use(function(req, res, next){
-        res.end(req.accepts(['text/html', 'application/json']) ? 'yup' : 'nope');
-      });
+      app.use((req, res, next) => {
+        res.end(req.accepts(['text/html', 'application/json']) ? 'yup' : 'nope')
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', 'foo/bar, bar/baz')
-      .expect('nope', done);
+        .get('/')
+        .set('Accept', 'foo/bar, bar/baz')
+        .expect('nope', done)
     })
 
-    it('should take quality into account', function(done){
-      var app = express();
+    it('should take quality into account', (done) => {
+      const app = express()
 
-      app.use(function(req, res, next){
-        res.end(req.accepts(['text/html', 'application/json']));
-      });
+      app.use((req, res, next) => {
+        res.end(req.accepts(['text/html', 'application/json']))
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', '*/html; q=.5, application/json')
-      .expect('application/json', done);
+        .get('/')
+        .set('Accept', '*/html; q=.5, application/json')
+        .expect('application/json', done)
     })
 
-    it('should return the first acceptable type with canonical mime types', function(done){
-      var app = express();
+    it('should return the first acceptable type with canonical mime types', (done) => {
+      const app = express()
 
-      app.use(function(req, res, next){
-        res.end(req.accepts(['application/json', 'text/html']));
-      });
+      app.use((req, res, next) => {
+        res.end(req.accepts(['application/json', 'text/html']))
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', '*/html')
-      .expect('text/html', done);
+        .get('/')
+        .set('Accept', '*/html')
+        .expect('text/html', done)
     })
   })
 })
diff --git a/test/req.acceptsCharsets.js b/test/req.acceptsCharsets.js
index 360a9878a78..21c66ae0c1b 100644
--- a/test/req.acceptsCharsets.js
+++ b/test/req.acceptsCharsets.js
@@ -1,49 +1,49 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.acceptsCharsets(type)', function(){
-    describe('when Accept-Charset is not present', function(){
-      it('should return true', function(done){
-        var app = express();
+describe('req', () => {
+  describe('.acceptsCharsets(type)', () => {
+    describe('when Accept-Charset is not present', () => {
+      it('should return true', (done) => {
+        const app = express()
 
-        app.use(function(req, res, next){
-          res.end(req.acceptsCharsets('utf-8') ? 'yes' : 'no');
-        });
+        app.use((req, res, next) => {
+          res.end(req.acceptsCharsets('utf-8') ? 'yes' : 'no')
+        })
 
         request(app)
-        .get('/')
-        .expect('yes', done);
+          .get('/')
+          .expect('yes', done)
       })
     })
 
-    describe('when Accept-Charset is present', function () {
-      it('should return true', function (done) {
-        var app = express();
+    describe('when Accept-Charset is present', () => {
+      it('should return true', (done) => {
+        const app = express()
 
-        app.use(function(req, res, next){
-          res.end(req.acceptsCharsets('utf-8') ? 'yes' : 'no');
-        });
+        app.use((req, res, next) => {
+          res.end(req.acceptsCharsets('utf-8') ? 'yes' : 'no')
+        })
 
         request(app)
-        .get('/')
-        .set('Accept-Charset', 'foo, bar, utf-8')
-        .expect('yes', done);
+          .get('/')
+          .set('Accept-Charset', 'foo, bar, utf-8')
+          .expect('yes', done)
       })
 
-      it('should return false otherwise', function(done){
-        var app = express();
+      it('should return false otherwise', (done) => {
+        const app = express()
 
-        app.use(function(req, res, next){
-          res.end(req.acceptsCharsets('utf-8') ? 'yes' : 'no');
-        });
+        app.use((req, res, next) => {
+          res.end(req.acceptsCharsets('utf-8') ? 'yes' : 'no')
+        })
 
         request(app)
-        .get('/')
-        .set('Accept-Charset', 'foo, bar')
-        .expect('no', done);
+          .get('/')
+          .set('Accept-Charset', 'foo, bar')
+          .expect('no', done)
       })
     })
   })
diff --git a/test/req.acceptsEncodings.js b/test/req.acceptsEncodings.js
index 9f8973cdfb8..0021fa1199d 100644
--- a/test/req.acceptsEncodings.js
+++ b/test/req.acceptsEncodings.js
@@ -1,14 +1,14 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.acceptsEncodings', function () {
-    it('should return encoding if accepted', function (done) {
-      var app = express();
+describe('req', () => {
+  describe('.acceptsEncodings', () => {
+    it('should return encoding if accepted', (done) => {
+      const app = express()
 
-      app.get('/', function (req, res) {
+      app.get('/', (req, res) => {
         res.send({
           gzip: req.acceptsEncodings('gzip'),
           deflate: req.acceptsEncodings('deflate')
@@ -21,10 +21,10 @@ describe('req', function(){
         .expect(200, { gzip: 'gzip', deflate: 'deflate' }, done)
     })
 
-    it('should be false if encoding not accepted', function(done){
-      var app = express();
+    it('should be false if encoding not accepted', (done) => {
+      const app = express()
 
-      app.get('/', function (req, res) {
+      app.get('/', (req, res) => {
         res.send({
           bogus: req.acceptsEncodings('bogus')
         })
diff --git a/test/req.acceptsLanguages.js b/test/req.acceptsLanguages.js
index e5629fbc323..7657c88393e 100644
--- a/test/req.acceptsLanguages.js
+++ b/test/req.acceptsLanguages.js
@@ -1,14 +1,14 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.acceptsLanguages', function(){
-    it('should return language if accepted', function (done) {
-      var app = express();
+describe('req', () => {
+  describe('.acceptsLanguages', () => {
+    it('should return language if accepted', (done) => {
+      const app = express()
 
-      app.get('/', function (req, res) {
+      app.get('/', (req, res) => {
         res.send({
           'en-us': req.acceptsLanguages('en-us'),
           en: req.acceptsLanguages('en')
@@ -21,10 +21,10 @@ describe('req', function(){
         .expect(200, { 'en-us': 'en-us', en: 'en' }, done)
     })
 
-    it('should be false if language not accepted', function(done){
-      var app = express();
+    it('should be false if language not accepted', (done) => {
+      const app = express()
 
-      app.get('/', function (req, res) {
+      app.get('/', (req, res) => {
         res.send({
           es: req.acceptsLanguages('es')
         })
@@ -36,11 +36,11 @@ describe('req', function(){
         .expect(200, { es: false }, done)
     })
 
-    describe('when Accept-Language is not present', function(){
-      it('should always return language', function (done) {
-        var app = express();
+    describe('when Accept-Language is not present', () => {
+      it('should always return language', (done) => {
+        const app = express()
 
-        app.get('/', function (req, res) {
+        app.get('/', (req, res) => {
           res.send({
             en: req.acceptsLanguages('en'),
             es: req.acceptsLanguages('es'),
diff --git a/test/req.baseUrl.js b/test/req.baseUrl.js
index b70803ea8bb..9c9919f017d 100644
--- a/test/req.baseUrl.js
+++ b/test/req.baseUrl.js
@@ -1,43 +1,43 @@
 'use strict'
 
-var express = require('..')
-var request = require('supertest')
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.baseUrl', function(){
-    it('should be empty for top-level route', function(done){
-      var app = express()
+describe('req', () => {
+  describe('.baseUrl', () => {
+    it('should be empty for top-level route', (done) => {
+      const app = express()
 
-      app.get('/:a', function(req, res){
+      app.get('/:a', (req, res) => {
         res.end(req.baseUrl)
       })
 
       request(app)
-      .get('/foo')
-      .expect(200, '', done)
+        .get('/foo')
+        .expect(200, '', done)
     })
 
-    it('should contain lower path', function(done){
-      var app = express()
-      var sub = express.Router()
+    it('should contain lower path', (done) => {
+      const app = express()
+      const sub = express.Router()
 
-      sub.get('/:b', function(req, res){
+      sub.get('/:b', (req, res) => {
         res.end(req.baseUrl)
       })
       app.use('/:a', sub)
 
       request(app)
-      .get('/foo/bar')
-      .expect(200, '/foo', done);
+        .get('/foo/bar')
+        .expect(200, '/foo', done)
     })
 
-    it('should contain full lower path', function(done){
-      var app = express()
-      var sub1 = express.Router()
-      var sub2 = express.Router()
-      var sub3 = express.Router()
+    it('should contain full lower path', (done) => {
+      const app = express()
+      const sub1 = express.Router()
+      const sub2 = express.Router()
+      const sub3 = express.Router()
 
-      sub3.get('/:d', function(req, res){
+      sub3.get('/:d', (req, res) => {
         res.end(req.baseUrl)
       })
       sub2.use('/:c', sub3)
@@ -45,44 +45,44 @@ describe('req', function(){
       app.use('/:a', sub1)
 
       request(app)
-      .get('/foo/bar/baz/zed')
-      .expect(200, '/foo/bar/baz', done);
+        .get('/foo/bar/baz/zed')
+        .expect(200, '/foo/bar/baz', done)
     })
 
-    it('should travel through routers correctly', function(done){
-      var urls = []
-      var app = express()
-      var sub1 = express.Router()
-      var sub2 = express.Router()
-      var sub3 = express.Router()
+    it('should travel through routers correctly', (done) => {
+      const urls = []
+      const app = express()
+      const sub1 = express.Router()
+      const sub2 = express.Router()
+      const sub3 = express.Router()
 
-      sub3.get('/:d', function(req, res, next){
+      sub3.get('/:d', (req, res, next) => {
         urls.push('0@' + req.baseUrl)
         next()
       })
       sub2.use('/:c', sub3)
-      sub1.use('/', function(req, res, next){
+      sub1.use('/', (req, res, next) => {
         urls.push('1@' + req.baseUrl)
         next()
       })
       sub1.use('/bar', sub2)
-      sub1.use('/bar', function(req, res, next){
+      sub1.use('/bar', (req, res, next) => {
         urls.push('2@' + req.baseUrl)
         next()
       })
-      app.use(function(req, res, next){
+      app.use((req, res, next) => {
         urls.push('3@' + req.baseUrl)
         next()
       })
       app.use('/:a', sub1)
-      app.use(function(req, res, next){
+      app.use((req, res, next) => {
         urls.push('4@' + req.baseUrl)
         res.end(urls.join(','))
       })
 
       request(app)
-      .get('/foo/bar/baz/zed')
-      .expect(200, '3@,1@/foo,0@/foo/bar/baz,2@/foo/bar,4@', done);
+        .get('/foo/bar/baz/zed')
+        .expect(200, '3@,1@/foo,0@/foo/bar/baz,2@/foo/bar,4@', done)
     })
   })
 })
diff --git a/test/req.fresh.js b/test/req.fresh.js
index 3bf6a1f65a7..fa95c659ac6 100644
--- a/test/req.fresh.js
+++ b/test/req.fresh.js
@@ -1,70 +1,69 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.fresh', function(){
-    it('should return true when the resource is not modified', function(done){
-      var app = express();
-      var etag = '"12345"';
+describe('req', () => {
+  describe('.fresh', () => {
+    it('should return true when the resource is not modified', (done) => {
+      const app = express()
+      const etag = '"12345"'
 
-      app.use(function(req, res){
-        res.set('ETag', etag);
-        res.send(req.fresh);
-      });
+      app.use((req, res) => {
+        res.set('ETag', etag)
+        res.send(req.fresh)
+      })
 
       request(app)
-      .get('/')
-      .set('If-None-Match', etag)
-      .expect(304, done);
+        .get('/')
+        .set('If-None-Match', etag)
+        .expect(304, done)
     })
 
-    it('should return false when the resource is modified', function(done){
-      var app = express();
+    it('should return false when the resource is modified', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.set('ETag', '"123"');
-        res.send(req.fresh);
-      });
+      app.use((req, res) => {
+        res.set('ETag', '"123"')
+        res.send(req.fresh)
+      })
 
       request(app)
-      .get('/')
-      .set('If-None-Match', '"12345"')
-      .expect(200, 'false', done);
+        .get('/')
+        .set('If-None-Match', '"12345"')
+        .expect(200, 'false', done)
     })
 
-    it('should return false without response headers', function(done){
-      var app = express();
+    it('should return false without response headers', (done) => {
+      const app = express()
 
       app.disable('x-powered-by')
-      app.use(function(req, res){
-        res.send(req.fresh);
-      });
+      app.use((req, res) => {
+        res.send(req.fresh)
+      })
 
       request(app)
-      .get('/')
-      .expect(200, 'false', done);
+        .get('/')
+        .expect(200, 'false', done)
     })
 
-    it('should ignore "If-Modified-Since" when "If-None-Match" is present', function(done) {
-      var app = express();
+    it('should ignore "If-Modified-Since" when "If-None-Match" is present', (done) => {
+      const app = express()
       const etag = '"FooBar"'
       const now = Date.now()
 
       app.disable('x-powered-by')
-      app.use(function(req, res) {
+      app.use((req, res) => {
         res.set('Etag', etag)
         res.set('Last-Modified', new Date(now).toUTCString())
-        res.send(req.fresh);
-      });
+        res.send(req.fresh)
+      })
 
       request(app)
         .get('/')
         .set('If-Modified-Since', new Date(now - 1000).toUTCString)
         .set('If-None-Match', etag)
-        .expect(304, done);
+        .expect(304, done)
     })
-
   })
 })
diff --git a/test/req.get.js b/test/req.get.js
index e73d109c84a..ca1b64b33af 100644
--- a/test/req.get.js
+++ b/test/req.get.js
@@ -1,60 +1,60 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest')
-  , assert = require('node:assert');
-
-describe('req', function(){
-  describe('.get(field)', function(){
-    it('should return the header field value', function(done){
-      var app = express();
-
-      app.use(function(req, res){
-        assert(req.get('Something-Else') === undefined);
-        res.end(req.get('Content-Type'));
-      });
+const express = require('../')
+const request = require('supertest')
+const assert = require('node:assert')
+
+describe('req', () => {
+  describe('.get(field)', () => {
+    it('should return the header field value', (done) => {
+      const app = express()
+
+      app.use((req, res) => {
+        assert(req.get('Something-Else') === undefined)
+        res.end(req.get('Content-Type'))
+      })
 
       request(app)
-      .post('/')
-      .set('Content-Type', 'application/json')
-      .expect('application/json', done);
+        .post('/')
+        .set('Content-Type', 'application/json')
+        .expect('application/json', done)
     })
 
-    it('should special-case Referer', function(done){
-      var app = express();
+    it('should special-case Referer', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.get('Referer'));
-      });
+      app.use((req, res) => {
+        res.end(req.get('Referer'))
+      })
 
       request(app)
-      .post('/')
-      .set('Referrer', 'http://foobar.com')
-      .expect('http://foobar.com', done);
+        .post('/')
+        .set('Referrer', 'http://foobar.com')
+        .expect('http://foobar.com', done)
     })
 
-    it('should throw missing header name', function (done) {
-      var app = express()
+    it('should throw missing header name', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.end(req.get())
       })
 
       request(app)
-      .get('/')
-      .expect(500, /TypeError: name argument is required to req.get/, done)
+        .get('/')
+        .expect(500, /TypeError: name argument is required to req.get/, done)
     })
 
-    it('should throw for non-string header name', function (done) {
-      var app = express()
+    it('should throw for non-string header name', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.end(req.get(42))
       })
 
       request(app)
-      .get('/')
-      .expect(500, /TypeError: name must be a string to req.get/, done)
+        .get('/')
+        .expect(500, /TypeError: name must be a string to req.get/, done)
     })
   })
 })
diff --git a/test/req.host.js b/test/req.host.js
index cdda82eaae3..136f0f7c371 100644
--- a/test/req.host.js
+++ b/test/req.host.js
@@ -1,155 +1,155 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest')
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.host', function(){
-    it('should return the Host when present', function(done){
-      var app = express();
+describe('req', () => {
+  describe('.host', () => {
+    it('should return the Host when present', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.host);
-      });
+      app.use((req, res) => {
+        res.end(req.host)
+      })
 
       request(app)
-      .post('/')
-      .set('Host', 'example.com')
-      .expect('example.com', done);
+        .post('/')
+        .set('Host', 'example.com')
+        .expect('example.com', done)
     })
 
-    it('should strip port number', function(done){
-      var app = express();
+    it('should strip port number', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.host);
-      });
+      app.use((req, res) => {
+        res.end(req.host)
+      })
 
       request(app)
-      .post('/')
-      .set('Host', 'example.com:3000')
-      .expect(200, 'example.com:3000', done);
+        .post('/')
+        .set('Host', 'example.com:3000')
+        .expect(200, 'example.com:3000', done)
     })
 
-    it('should return undefined otherwise', function(done){
-      var app = express();
+    it('should return undefined otherwise', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        req.headers.host = null;
-        res.end(String(req.host));
-      });
+      app.use((req, res) => {
+        req.headers.host = null
+        res.end(String(req.host))
+      })
 
       request(app)
-      .post('/')
-      .expect('undefined', done);
+        .post('/')
+        .expect('undefined', done)
     })
 
-    it('should work with IPv6 Host', function(done){
-      var app = express();
+    it('should work with IPv6 Host', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.host);
-      });
+      app.use((req, res) => {
+        res.end(req.host)
+      })
 
       request(app)
-      .post('/')
-      .set('Host', '[::1]')
-      .expect('[::1]', done);
+        .post('/')
+        .set('Host', '[::1]')
+        .expect('[::1]', done)
     })
 
-    it('should work with IPv6 Host and port', function(done){
-      var app = express();
+    it('should work with IPv6 Host and port', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.host);
-      });
+      app.use((req, res) => {
+        res.end(req.host)
+      })
 
       request(app)
-      .post('/')
-      .set('Host', '[::1]:3000')
-      .expect(200, '[::1]:3000', done);
+        .post('/')
+        .set('Host', '[::1]:3000')
+        .expect(200, '[::1]:3000', done)
     })
 
-    describe('when "trust proxy" is enabled', function(){
-      it('should respect X-Forwarded-Host', function(done){
-        var app = express();
+    describe('when "trust proxy" is enabled', () => {
+      it('should respect X-Forwarded-Host', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.use(function(req, res){
-          res.end(req.host);
-        });
+        app.use((req, res) => {
+          res.end(req.host)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'localhost')
-        .set('X-Forwarded-Host', 'example.com')
-        .expect('example.com', done);
+          .get('/')
+          .set('Host', 'localhost')
+          .set('X-Forwarded-Host', 'example.com')
+          .expect('example.com', done)
       })
 
-      it('should ignore X-Forwarded-Host if socket addr not trusted', function(done){
-        var app = express();
+      it('should ignore X-Forwarded-Host if socket addr not trusted', (done) => {
+        const app = express()
 
-        app.set('trust proxy', '10.0.0.1');
+        app.set('trust proxy', '10.0.0.1')
 
-        app.use(function(req, res){
-          res.end(req.host);
-        });
+        app.use((req, res) => {
+          res.end(req.host)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'localhost')
-        .set('X-Forwarded-Host', 'example.com')
-        .expect('localhost', done);
+          .get('/')
+          .set('Host', 'localhost')
+          .set('X-Forwarded-Host', 'example.com')
+          .expect('localhost', done)
       })
 
-      it('should default to Host', function(done){
-        var app = express();
+      it('should default to Host', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.use(function(req, res){
-          res.end(req.host);
-        });
+        app.use((req, res) => {
+          res.end(req.host)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'example.com')
-        .expect('example.com', done);
+          .get('/')
+          .set('Host', 'example.com')
+          .expect('example.com', done)
       })
 
-      describe('when trusting hop count', function () {
-        it('should respect X-Forwarded-Host', function (done) {
-          var app = express();
+      describe('when trusting hop count', () => {
+        it('should respect X-Forwarded-Host', (done) => {
+          const app = express()
 
-          app.set('trust proxy', 1);
+          app.set('trust proxy', 1)
 
-          app.use(function (req, res) {
-            res.end(req.host);
-          });
+          app.use((req, res) => {
+            res.end(req.host)
+          })
 
           request(app)
-          .get('/')
-          .set('Host', 'localhost')
-          .set('X-Forwarded-Host', 'example.com')
-          .expect('example.com', done);
+            .get('/')
+            .set('Host', 'localhost')
+            .set('X-Forwarded-Host', 'example.com')
+            .expect('example.com', done)
         })
       })
     })
 
-    describe('when "trust proxy" is disabled', function(){
-      it('should ignore X-Forwarded-Host', function(done){
-        var app = express();
+    describe('when "trust proxy" is disabled', () => {
+      it('should ignore X-Forwarded-Host', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.end(req.host);
-        });
+        app.use((req, res) => {
+          res.end(req.host)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'localhost')
-        .set('X-Forwarded-Host', 'evil')
-        .expect('localhost', done);
+          .get('/')
+          .set('Host', 'localhost')
+          .set('X-Forwarded-Host', 'evil')
+          .expect('localhost', done)
       })
     })
   })
diff --git a/test/req.hostname.js b/test/req.hostname.js
index b3716b566ae..4b12e951fb9 100644
--- a/test/req.hostname.js
+++ b/test/req.hostname.js
@@ -1,187 +1,187 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest')
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.hostname', function(){
-    it('should return the Host when present', function(done){
-      var app = express();
+describe('req', () => {
+  describe('.hostname', () => {
+    it('should return the Host when present', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.hostname);
-      });
+      app.use((req, res) => {
+        res.end(req.hostname)
+      })
 
       request(app)
-      .post('/')
-      .set('Host', 'example.com')
-      .expect('example.com', done);
+        .post('/')
+        .set('Host', 'example.com')
+        .expect('example.com', done)
     })
 
-    it('should strip port number', function(done){
-      var app = express();
+    it('should strip port number', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.hostname);
-      });
+      app.use((req, res) => {
+        res.end(req.hostname)
+      })
 
       request(app)
-      .post('/')
-      .set('Host', 'example.com:3000')
-      .expect('example.com', done);
+        .post('/')
+        .set('Host', 'example.com:3000')
+        .expect('example.com', done)
     })
 
-    it('should return undefined otherwise', function(done){
-      var app = express();
+    it('should return undefined otherwise', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        req.headers.host = null;
-        res.end(String(req.hostname));
-      });
+      app.use((req, res) => {
+        req.headers.host = null
+        res.end(String(req.hostname))
+      })
 
       request(app)
-      .post('/')
-      .expect('undefined', done);
+        .post('/')
+        .expect('undefined', done)
     })
 
-    it('should work with IPv6 Host', function(done){
-      var app = express();
+    it('should work with IPv6 Host', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.hostname);
-      });
+      app.use((req, res) => {
+        res.end(req.hostname)
+      })
 
       request(app)
-      .post('/')
-      .set('Host', '[::1]')
-      .expect('[::1]', done);
+        .post('/')
+        .set('Host', '[::1]')
+        .expect('[::1]', done)
     })
 
-    it('should work with IPv6 Host and port', function(done){
-      var app = express();
+    it('should work with IPv6 Host and port', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.hostname);
-      });
+      app.use((req, res) => {
+        res.end(req.hostname)
+      })
 
       request(app)
-      .post('/')
-      .set('Host', '[::1]:3000')
-      .expect('[::1]', done);
+        .post('/')
+        .set('Host', '[::1]:3000')
+        .expect('[::1]', done)
     })
 
-    describe('when "trust proxy" is enabled', function(){
-      it('should respect X-Forwarded-Host', function(done){
-        var app = express();
+    describe('when "trust proxy" is enabled', () => {
+      it('should respect X-Forwarded-Host', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.use(function(req, res){
-          res.end(req.hostname);
-        });
+        app.use((req, res) => {
+          res.end(req.hostname)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'localhost')
-        .set('X-Forwarded-Host', 'example.com:3000')
-        .expect('example.com', done);
+          .get('/')
+          .set('Host', 'localhost')
+          .set('X-Forwarded-Host', 'example.com:3000')
+          .expect('example.com', done)
       })
 
-      it('should ignore X-Forwarded-Host if socket addr not trusted', function(done){
-        var app = express();
+      it('should ignore X-Forwarded-Host if socket addr not trusted', (done) => {
+        const app = express()
 
-        app.set('trust proxy', '10.0.0.1');
+        app.set('trust proxy', '10.0.0.1')
 
-        app.use(function(req, res){
-          res.end(req.hostname);
-        });
+        app.use((req, res) => {
+          res.end(req.hostname)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'localhost')
-        .set('X-Forwarded-Host', 'example.com')
-        .expect('localhost', done);
+          .get('/')
+          .set('Host', 'localhost')
+          .set('X-Forwarded-Host', 'example.com')
+          .expect('localhost', done)
       })
 
-      it('should default to Host', function(done){
-        var app = express();
+      it('should default to Host', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.use(function(req, res){
-          res.end(req.hostname);
-        });
+        app.use((req, res) => {
+          res.end(req.hostname)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'example.com')
-        .expect('example.com', done);
+          .get('/')
+          .set('Host', 'example.com')
+          .expect('example.com', done)
       })
 
-      describe('when multiple X-Forwarded-Host', function () {
-        it('should use the first value', function (done) {
-          var app = express()
+      describe('when multiple X-Forwarded-Host', () => {
+        it('should use the first value', (done) => {
+          const app = express()
 
           app.enable('trust proxy')
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.send(req.hostname)
           })
 
           request(app)
-          .get('/')
-          .set('Host', 'localhost')
-          .set('X-Forwarded-Host', 'example.com, foobar.com')
-          .expect(200, 'example.com', done)
+            .get('/')
+            .set('Host', 'localhost')
+            .set('X-Forwarded-Host', 'example.com, foobar.com')
+            .expect(200, 'example.com', done)
         })
 
-        it('should remove OWS around comma', function (done) {
-          var app = express()
+        it('should remove OWS around comma', (done) => {
+          const app = express()
 
           app.enable('trust proxy')
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.send(req.hostname)
           })
 
           request(app)
-          .get('/')
-          .set('Host', 'localhost')
-          .set('X-Forwarded-Host', 'example.com , foobar.com')
-          .expect(200, 'example.com', done)
+            .get('/')
+            .set('Host', 'localhost')
+            .set('X-Forwarded-Host', 'example.com , foobar.com')
+            .expect(200, 'example.com', done)
         })
 
-        it('should strip port number', function (done) {
-          var app = express()
+        it('should strip port number', (done) => {
+          const app = express()
 
           app.enable('trust proxy')
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.send(req.hostname)
           })
 
           request(app)
-          .get('/')
-          .set('Host', 'localhost')
-          .set('X-Forwarded-Host', 'example.com:8080 , foobar.com:8888')
-          .expect(200, 'example.com', done)
+            .get('/')
+            .set('Host', 'localhost')
+            .set('X-Forwarded-Host', 'example.com:8080 , foobar.com:8888')
+            .expect(200, 'example.com', done)
         })
       })
     })
 
-    describe('when "trust proxy" is disabled', function(){
-      it('should ignore X-Forwarded-Host', function(done){
-        var app = express();
+    describe('when "trust proxy" is disabled', () => {
+      it('should ignore X-Forwarded-Host', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.end(req.hostname);
-        });
+        app.use((req, res) => {
+          res.end(req.hostname)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'localhost')
-        .set('X-Forwarded-Host', 'evil')
-        .expect('localhost', done);
+          .get('/')
+          .set('Host', 'localhost')
+          .set('X-Forwarded-Host', 'evil')
+          .expect('localhost', done)
       })
     })
   })
diff --git a/test/req.ip.js b/test/req.ip.js
index 6bb3c5ac52f..067233bcae2 100644
--- a/test/req.ip.js
+++ b/test/req.ip.js
@@ -1,48 +1,48 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.ip', function(){
-    describe('when X-Forwarded-For is present', function(){
-      describe('when "trust proxy" is enabled', function(){
-        it('should return the client addr', function(done){
-          var app = express();
+describe('req', () => {
+  describe('.ip', () => {
+    describe('when X-Forwarded-For is present', () => {
+      describe('when "trust proxy" is enabled', () => {
+        it('should return the client addr', (done) => {
+          const app = express()
 
-          app.enable('trust proxy');
+          app.enable('trust proxy')
 
-          app.use(function(req, res, next){
-            res.send(req.ip);
-          });
+          app.use((req, res, next) => {
+            res.send(req.ip)
+          })
 
           request(app)
-          .get('/')
-          .set('X-Forwarded-For', 'client, p1, p2')
-          .expect('client', done);
+            .get('/')
+            .set('X-Forwarded-For', 'client, p1, p2')
+            .expect('client', done)
         })
 
-        it('should return the addr after trusted proxy based on count', function (done) {
-          var app = express();
+        it('should return the addr after trusted proxy based on count', (done) => {
+          const app = express()
 
-          app.set('trust proxy', 2);
+          app.set('trust proxy', 2)
 
-          app.use(function(req, res, next){
-            res.send(req.ip);
-          });
+          app.use((req, res, next) => {
+            res.send(req.ip)
+          })
 
           request(app)
-          .get('/')
-          .set('X-Forwarded-For', 'client, p1, p2')
-          .expect('p1', done);
+            .get('/')
+            .set('X-Forwarded-For', 'client, p1, p2')
+            .expect('p1', done)
         })
 
-        it('should return the addr after trusted proxy based on list', function (done) {
-          var app = express()
+        it('should return the addr after trusted proxy based on list', (done) => {
+          const app = express()
 
           app.set('trust proxy', '10.0.0.1, 10.0.0.2, 127.0.0.1, ::1')
 
-          app.get('/', function (req, res) {
+          app.get('/', (req, res) => {
             res.send(req.ip)
           })
 
@@ -52,50 +52,50 @@ describe('req', function(){
             .expect('10.0.0.3', done)
         })
 
-        it('should return the addr after trusted proxy, from sub app', function (done) {
-          var app = express();
-          var sub = express();
+        it('should return the addr after trusted proxy, from sub app', (done) => {
+          const app = express()
+          const sub = express()
 
-          app.set('trust proxy', 2);
-          app.use(sub);
+          app.set('trust proxy', 2)
+          app.use(sub)
 
-          sub.use(function (req, res, next) {
-            res.send(req.ip);
-          });
+          sub.use((req, res, next) => {
+            res.send(req.ip)
+          })
 
           request(app)
-          .get('/')
-          .set('X-Forwarded-For', 'client, p1, p2')
-          .expect(200, 'p1', done);
+            .get('/')
+            .set('X-Forwarded-For', 'client, p1, p2')
+            .expect(200, 'p1', done)
         })
       })
 
-      describe('when "trust proxy" is disabled', function(){
-        it('should return the remote address', function(done){
-          var app = express();
+      describe('when "trust proxy" is disabled', () => {
+        it('should return the remote address', (done) => {
+          const app = express()
 
-          app.use(function(req, res, next){
-            res.send(req.ip);
-          });
+          app.use((req, res, next) => {
+            res.send(req.ip)
+          })
 
-          var test = request(app).get('/')
+          const test = request(app).get('/')
           test.set('X-Forwarded-For', 'client, p1, p2')
-          test.expect(200, getExpectedClientAddress(test._server), done);
+          test.expect(200, getExpectedClientAddress(test._server), done)
         })
       })
     })
 
-    describe('when X-Forwarded-For is not present', function(){
-      it('should return the remote address', function(done){
-        var app = express();
+    describe('when X-Forwarded-For is not present', () => {
+      it('should return the remote address', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.use(function(req, res, next){
-          res.send(req.ip);
-        });
+        app.use((req, res, next) => {
+          res.send(req.ip)
+        })
 
-        var test = request(app).get('/')
+        const test = request(app).get('/')
         test.expect(200, getExpectedClientAddress(test._server), done)
       })
     })
@@ -106,8 +106,8 @@ describe('req', function(){
  * Get the local client address depending on AF_NET of server
  */
 
-function getExpectedClientAddress(server) {
+function getExpectedClientAddress (server) {
   return server.address().address === '::'
     ? '::ffff:127.0.0.1'
-    : '127.0.0.1';
+    : '127.0.0.1'
 }
diff --git a/test/req.ips.js b/test/req.ips.js
index 2f9a0736ea3..5a1fd4bed9f 100644
--- a/test/req.ips.js
+++ b/test/req.ips.js
@@ -1,70 +1,70 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.ips', function(){
-    describe('when X-Forwarded-For is present', function(){
-      describe('when "trust proxy" is enabled', function(){
-        it('should return an array of the specified addresses', function(done){
-          var app = express();
+describe('req', () => {
+  describe('.ips', () => {
+    describe('when X-Forwarded-For is present', () => {
+      describe('when "trust proxy" is enabled', () => {
+        it('should return an array of the specified addresses', (done) => {
+          const app = express()
 
-          app.enable('trust proxy');
+          app.enable('trust proxy')
 
-          app.use(function(req, res, next){
-            res.send(req.ips);
-          });
+          app.use((req, res, next) => {
+            res.send(req.ips)
+          })
 
           request(app)
-          .get('/')
-          .set('X-Forwarded-For', 'client, p1, p2')
-          .expect('["client","p1","p2"]', done);
+            .get('/')
+            .set('X-Forwarded-For', 'client, p1, p2')
+            .expect('["client","p1","p2"]', done)
         })
 
-        it('should stop at first untrusted', function(done){
-          var app = express();
+        it('should stop at first untrusted', (done) => {
+          const app = express()
 
-          app.set('trust proxy', 2);
+          app.set('trust proxy', 2)
 
-          app.use(function(req, res, next){
-            res.send(req.ips);
-          });
+          app.use((req, res, next) => {
+            res.send(req.ips)
+          })
 
           request(app)
-          .get('/')
-          .set('X-Forwarded-For', 'client, p1, p2')
-          .expect('["p1","p2"]', done);
+            .get('/')
+            .set('X-Forwarded-For', 'client, p1, p2')
+            .expect('["p1","p2"]', done)
         })
       })
 
-      describe('when "trust proxy" is disabled', function(){
-        it('should return an empty array', function(done){
-          var app = express();
+      describe('when "trust proxy" is disabled', () => {
+        it('should return an empty array', (done) => {
+          const app = express()
 
-          app.use(function(req, res, next){
-            res.send(req.ips);
-          });
+          app.use((req, res, next) => {
+            res.send(req.ips)
+          })
 
           request(app)
-          .get('/')
-          .set('X-Forwarded-For', 'client, p1, p2')
-          .expect('[]', done);
+            .get('/')
+            .set('X-Forwarded-For', 'client, p1, p2')
+            .expect('[]', done)
         })
       })
     })
 
-    describe('when X-Forwarded-For is not present', function(){
-      it('should return []', function(done){
-        var app = express();
+    describe('when X-Forwarded-For is not present', () => {
+      it('should return []', (done) => {
+        const app = express()
 
-        app.use(function(req, res, next){
-          res.send(req.ips);
-        });
+        app.use((req, res, next) => {
+          res.send(req.ips)
+        })
 
         request(app)
-        .get('/')
-        .expect('[]', done);
+          .get('/')
+          .expect('[]', done)
       })
     })
   })
diff --git a/test/req.is.js b/test/req.is.js
index c5904dd600a..a1573a385db 100644
--- a/test/req.is.js
+++ b/test/req.is.js
@@ -1,169 +1,169 @@
 'use strict'
 
-var express = require('..')
-var request = require('supertest')
+const express = require('../')
+const request = require('supertest')
 
-describe('req.is()', function () {
-  describe('when given a mime type', function () {
-    it('should return the type when matching', function (done) {
-      var app = express()
+describe('req.is()', () => {
+  describe('when given a mime type', () => {
+    it('should return the type when matching', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('application/json'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json')
-      .send('{}')
-      .expect(200, '"application/json"', done)
+        .post('/')
+        .type('application/json')
+        .send('{}')
+        .expect(200, '"application/json"', done)
     })
 
-    it('should return false when not matching', function (done) {
-      var app = express()
+    it('should return false when not matching', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('image/jpeg'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json')
-      .send('{}')
-      .expect(200, 'false', done)
+        .post('/')
+        .type('application/json')
+        .send('{}')
+        .expect(200, 'false', done)
     })
 
-    it('should ignore charset', function (done) {
-      var app = express()
+    it('should ignore charset', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('application/json'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json; charset=UTF-8')
-      .send('{}')
-      .expect(200, '"application/json"', done)
+        .post('/')
+        .type('application/json; charset=UTF-8')
+        .send('{}')
+        .expect(200, '"application/json"', done)
     })
   })
 
-  describe('when content-type is not present', function(){
-    it('should return false', function (done) {
-      var app = express()
+  describe('when content-type is not present', () => {
+    it('should return false', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('application/json'))
       })
 
       request(app)
-      .post('/')
-      .send('{}')
-      .expect(200, 'false', done)
+        .post('/')
+        .send('{}')
+        .expect(200, 'false', done)
     })
   })
 
-  describe('when given an extension', function(){
-    it('should lookup the mime type', function (done) {
-      var app = express()
+  describe('when given an extension', () => {
+    it('should lookup the mime type', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('json'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json')
-      .send('{}')
-      .expect(200, '"json"', done)
+        .post('/')
+        .type('application/json')
+        .send('{}')
+        .expect(200, '"json"', done)
     })
   })
 
-  describe('when given */subtype', function(){
-    it('should return the full type when matching', function (done) {
-      var app = express()
+  describe('when given */subtype', () => {
+    it('should return the full type when matching', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('*/json'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json')
-      .send('{}')
-      .expect(200, '"application/json"', done)
+        .post('/')
+        .type('application/json')
+        .send('{}')
+        .expect(200, '"application/json"', done)
     })
 
-    it('should return false when not matching', function (done) {
-      var app = express()
+    it('should return false when not matching', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('*/html'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json')
-      .send('{}')
-      .expect(200, 'false', done)
+        .post('/')
+        .type('application/json')
+        .send('{}')
+        .expect(200, 'false', done)
     })
 
-    it('should ignore charset', function (done) {
-      var app = express()
+    it('should ignore charset', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('*/json'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json; charset=UTF-8')
-      .send('{}')
-      .expect(200, '"application/json"', done)
+        .post('/')
+        .type('application/json; charset=UTF-8')
+        .send('{}')
+        .expect(200, '"application/json"', done)
     })
   })
 
-  describe('when given type/*', function(){
-    it('should return the full type when matching', function (done) {
-      var app = express()
+  describe('when given type/*', () => {
+    it('should return the full type when matching', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('application/*'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json')
-      .send('{}')
-      .expect(200, '"application/json"', done)
+        .post('/')
+        .type('application/json')
+        .send('{}')
+        .expect(200, '"application/json"', done)
     })
 
-    it('should return false when not matching', function (done) {
-      var app = express()
+    it('should return false when not matching', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('text/*'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json')
-      .send('{}')
-      .expect(200, 'false', done)
+        .post('/')
+        .type('application/json')
+        .send('{}')
+        .expect(200, 'false', done)
     })
 
-    it('should ignore charset', function (done) {
-      var app = express()
+    it('should ignore charset', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.is('application/*'))
       })
 
       request(app)
-      .post('/')
-      .type('application/json; charset=UTF-8')
-      .send('{}')
-      .expect(200, '"application/json"', done)
+        .post('/')
+        .type('application/json; charset=UTF-8')
+        .send('{}')
+        .expect(200, '"application/json"', done)
     })
   })
 })
diff --git a/test/req.path.js b/test/req.path.js
index 3ff6177c74e..21f4d5bb1e1 100644
--- a/test/req.path.js
+++ b/test/req.path.js
@@ -1,20 +1,20 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.path', function(){
-    it('should return the parsed pathname', function(done){
-      var app = express();
+describe('req', () => {
+  describe('.path', () => {
+    it('should return the parsed pathname', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.path);
-      });
+      app.use((req, res) => {
+        res.end(req.path)
+      })
 
       request(app)
-      .get('/login?redirect=/post/1/comments')
-      .expect('/login', done);
+        .get('/login?redirect=/post/1/comments')
+        .expect('/login', done)
     })
   })
 })
diff --git a/test/req.protocol.js b/test/req.protocol.js
index def82eda922..a5d52a7053d 100644
--- a/test/req.protocol.js
+++ b/test/req.protocol.js
@@ -1,112 +1,112 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.protocol', function(){
-    it('should return the protocol string', function(done){
-      var app = express();
+describe('req', () => {
+  describe('.protocol', () => {
+    it('should return the protocol string', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.end(req.protocol);
-      });
+      app.use((req, res) => {
+        res.end(req.protocol)
+      })
 
       request(app)
-      .get('/')
-      .expect('http', done);
+        .get('/')
+        .expect('http', done)
     })
 
-    describe('when "trust proxy" is enabled', function(){
-      it('should respect X-Forwarded-Proto', function(done){
-        var app = express();
+    describe('when "trust proxy" is enabled', () => {
+      it('should respect X-Forwarded-Proto', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.use(function(req, res){
-          res.end(req.protocol);
-        });
+        app.use((req, res) => {
+          res.end(req.protocol)
+        })
 
         request(app)
-        .get('/')
-        .set('X-Forwarded-Proto', 'https')
-        .expect('https', done);
+          .get('/')
+          .set('X-Forwarded-Proto', 'https')
+          .expect('https', done)
       })
 
-      it('should default to the socket addr if X-Forwarded-Proto not present', function(done){
-        var app = express();
+      it('should default to the socket addr if X-Forwarded-Proto not present', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.use(function(req, res){
-          req.socket.encrypted = true;
-          res.end(req.protocol);
-        });
+        app.use((req, res) => {
+          req.socket.encrypted = true
+          res.end(req.protocol)
+        })
 
         request(app)
-        .get('/')
-        .expect('https', done);
+          .get('/')
+          .expect('https', done)
       })
 
-      it('should ignore X-Forwarded-Proto if socket addr not trusted', function(done){
-        var app = express();
+      it('should ignore X-Forwarded-Proto if socket addr not trusted', (done) => {
+        const app = express()
 
-        app.set('trust proxy', '10.0.0.1');
+        app.set('trust proxy', '10.0.0.1')
 
-        app.use(function(req, res){
-          res.end(req.protocol);
-        });
+        app.use((req, res) => {
+          res.end(req.protocol)
+        })
 
         request(app)
-        .get('/')
-        .set('X-Forwarded-Proto', 'https')
-        .expect('http', done);
+          .get('/')
+          .set('X-Forwarded-Proto', 'https')
+          .expect('http', done)
       })
 
-      it('should default to http', function(done){
-        var app = express();
+      it('should default to http', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.use(function(req, res){
-          res.end(req.protocol);
-        });
+        app.use((req, res) => {
+          res.end(req.protocol)
+        })
 
         request(app)
-        .get('/')
-        .expect('http', done);
+          .get('/')
+          .expect('http', done)
       })
 
-      describe('when trusting hop count', function () {
-        it('should respect X-Forwarded-Proto', function (done) {
-          var app = express();
+      describe('when trusting hop count', () => {
+        it('should respect X-Forwarded-Proto', (done) => {
+          const app = express()
 
-          app.set('trust proxy', 1);
+          app.set('trust proxy', 1)
 
-          app.use(function (req, res) {
-            res.end(req.protocol);
-          });
+          app.use((req, res) => {
+            res.end(req.protocol)
+          })
 
           request(app)
-          .get('/')
-          .set('X-Forwarded-Proto', 'https')
-          .expect('https', done);
+            .get('/')
+            .set('X-Forwarded-Proto', 'https')
+            .expect('https', done)
         })
       })
     })
 
-    describe('when "trust proxy" is disabled', function(){
-      it('should ignore X-Forwarded-Proto', function(done){
-        var app = express();
+    describe('when "trust proxy" is disabled', () => {
+      it('should ignore X-Forwarded-Proto', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.end(req.protocol);
-        });
+        app.use((req, res) => {
+          res.end(req.protocol)
+        })
 
         request(app)
-        .get('/')
-        .set('X-Forwarded-Proto', 'https')
-        .expect('http', done);
+          .get('/')
+          .set('X-Forwarded-Proto', 'https')
+          .expect('http', done)
       })
     })
   })
diff --git a/test/req.query.js b/test/req.query.js
index c0d3c8376e9..1a27bb5dc1d 100644
--- a/test/req.query.js
+++ b/test/req.query.js
@@ -1,106 +1,104 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('../')
-  , request = require('supertest');
+const assert = require('node:assert')
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.query', function(){
-    it('should default to {}', function(done){
-      var app = createApp();
+describe('req', () => {
+  describe('.query', () => {
+    it('should default to {}', (done) => {
+      const app = createApp()
 
       request(app)
-      .get('/')
-      .expect(200, '{}', done);
-    });
+        .get('/')
+        .expect(200, '{}', done)
+    })
 
-    it('should default to parse simple keys', function (done) {
-      var app = createApp();
+    it('should default to parse simple keys', (done) => {
+      const app = createApp()
 
       request(app)
-      .get('/?user[name]=tj')
-      .expect(200, '{"user[name]":"tj"}', done);
-    });
+        .get('/?user[name]=tj')
+        .expect(200, '{"user[name]":"tj"}', done)
+    })
 
-    describe('when "query parser" is extended', function () {
-      it('should parse complex keys', function (done) {
-        var app = createApp('extended');
+    describe('when "query parser" is extended', () => {
+      it('should parse complex keys', (done) => {
+        const app = createApp('extended')
 
         request(app)
-        .get('/?foo[0][bar]=baz&foo[0][fizz]=buzz&foo[]=done!')
-        .expect(200, '{"foo":[{"bar":"baz","fizz":"buzz"},"done!"]}', done);
-      });
+          .get('/?foo[0][bar]=baz&foo[0][fizz]=buzz&foo[]=done!')
+          .expect(200, '{"foo":[{"bar":"baz","fizz":"buzz"},"done!"]}', done)
+      })
 
-      it('should parse parameters with dots', function (done) {
-        var app = createApp('extended');
+      it('should parse parameters with dots', (done) => {
+        const app = createApp('extended')
 
         request(app)
-        .get('/?user.name=tj')
-        .expect(200, '{"user.name":"tj"}', done);
-      });
-    });
+          .get('/?user.name=tj')
+          .expect(200, '{"user.name":"tj"}', done)
+      })
+    })
 
-    describe('when "query parser" is simple', function () {
-      it('should not parse complex keys', function (done) {
-        var app = createApp('simple');
+    describe('when "query parser" is simple', () => {
+      it('should not parse complex keys', (done) => {
+        const app = createApp('simple')
 
         request(app)
-        .get('/?user%5Bname%5D=tj')
-        .expect(200, '{"user[name]":"tj"}', done);
-      });
-    });
+          .get('/?user%5Bname%5D=tj')
+          .expect(200, '{"user[name]":"tj"}', done)
+      })
+    })
 
-    describe('when "query parser" is a function', function () {
-      it('should parse using function', function (done) {
-        var app = createApp(function (str) {
-          return {'length': (str || '').length};
-        });
+    describe('when "query parser" is a function', () => {
+      it('should parse using function', (done) => {
+        const app = createApp((str) => ({ length: (str || '').length }))
 
         request(app)
-        .get('/?user%5Bname%5D=tj')
-        .expect(200, '{"length":17}', done);
-      });
-    });
+          .get('/?user%5Bname%5D=tj')
+          .expect(200, '{"length":17}', done)
+      })
+    })
 
-    describe('when "query parser" disabled', function () {
-      it('should not parse query', function (done) {
-        var app = createApp(false);
+    describe('when "query parser" disabled', () => {
+      it('should not parse query', (done) => {
+        const app = createApp(false)
 
         request(app)
-        .get('/?user%5Bname%5D=tj')
-        .expect(200, '{}', done);
-      });
-    });
+          .get('/?user%5Bname%5D=tj')
+          .expect(200, '{}', done)
+      })
+    })
 
-    describe('when "query parser" enabled', function () {
-      it('should not parse complex keys', function (done) {
-        var app = createApp(true);
+    describe('when "query parser" enabled', () => {
+      it('should not parse complex keys', (done) => {
+        const app = createApp(true)
 
         request(app)
-        .get('/?user%5Bname%5D=tj')
-        .expect(200, '{"user[name]":"tj"}', done);
-      });
-    });
+          .get('/?user%5Bname%5D=tj')
+          .expect(200, '{"user[name]":"tj"}', done)
+      })
+    })
 
-    describe('when "query parser" an unknown value', function () {
-      it('should throw', function () {
+    describe('when "query parser" an unknown value', () => {
+      it('should throw', () => {
         assert.throws(createApp.bind(null, 'bogus'),
           /unknown value.*query parser/)
-      });
-    });
+      })
+    })
   })
 })
 
-function createApp(setting) {
-  var app = express();
+function createApp (setting) {
+  const app = express()
 
   if (setting !== undefined) {
-    app.set('query parser', setting);
+    app.set('query parser', setting)
   }
 
-  app.use(function (req, res) {
-    res.send(req.query);
-  });
+  app.use((req, res) => {
+    res.send(req.query)
+  })
 
-  return app;
+  return app
 }
diff --git a/test/req.range.js b/test/req.range.js
index 111441736eb..50a3c9f5ea1 100644
--- a/test/req.range.js
+++ b/test/req.range.js
@@ -1,103 +1,103 @@
 'use strict'
 
-var express = require('..');
-var request = require('supertest')
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.range(size)', function(){
-    it('should return parsed ranges', function (done) {
-      var app = express()
+describe('req', () => {
+  describe('.range(size)', () => {
+    it('should return parsed ranges', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.range(120))
       })
 
       request(app)
-      .get('/')
-      .set('Range', 'bytes=0-50,51-100')
-      .expect(200, '[{"start":0,"end":50},{"start":51,"end":100}]', done)
+        .get('/')
+        .set('Range', 'bytes=0-50,51-100')
+        .expect(200, '[{"start":0,"end":50},{"start":51,"end":100}]', done)
     })
 
-    it('should cap to the given size', function (done) {
-      var app = express()
+    it('should cap to the given size', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.range(75))
       })
 
       request(app)
-      .get('/')
-      .set('Range', 'bytes=0-100')
-      .expect(200, '[{"start":0,"end":74}]', done)
+        .get('/')
+        .set('Range', 'bytes=0-100')
+        .expect(200, '[{"start":0,"end":74}]', done)
     })
 
-    it('should cap to the given size when open-ended', function (done) {
-      var app = express()
+    it('should cap to the given size when open-ended', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.range(75))
       })
 
       request(app)
-      .get('/')
-      .set('Range', 'bytes=0-')
-      .expect(200, '[{"start":0,"end":74}]', done)
+        .get('/')
+        .set('Range', 'bytes=0-')
+        .expect(200, '[{"start":0,"end":74}]', done)
     })
 
-    it('should have a .type', function (done) {
-      var app = express()
+    it('should have a .type', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.range(120).type)
       })
 
       request(app)
-      .get('/')
-      .set('Range', 'bytes=0-100')
-      .expect(200, '"bytes"', done)
+        .get('/')
+        .set('Range', 'bytes=0-100')
+        .expect(200, '"bytes"', done)
     })
 
-    it('should accept any type', function (done) {
-      var app = express()
+    it('should accept any type', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.json(req.range(120).type)
       })
 
       request(app)
-      .get('/')
-      .set('Range', 'users=0-2')
-      .expect(200, '"users"', done)
+        .get('/')
+        .set('Range', 'users=0-2')
+        .expect(200, '"users"', done)
     })
 
-    it('should return undefined if no range', function (done) {
-      var app = express()
+    it('should return undefined if no range', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.send(String(req.range(120)))
       })
 
       request(app)
-      .get('/')
-      .expect(200, 'undefined', done)
+        .get('/')
+        .expect(200, 'undefined', done)
     })
   })
 
-  describe('.range(size, options)', function(){
-    describe('with "combine: true" option', function(){
-      it('should return combined ranges', function (done) {
-        var app = express()
+  describe('.range(size, options)', () => {
+    describe('with "combine: true" option', () => {
+      it('should return combined ranges', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.json(req.range(120, {
             combine: true
           }))
         })
 
         request(app)
-        .get('/')
-        .set('Range', 'bytes=0-50,51-100')
-        .expect(200, '[{"start":0,"end":100}]', done)
+          .get('/')
+          .set('Range', 'bytes=0-50,51-100')
+          .expect(200, '[{"start":0,"end":100}]', done)
       })
     })
   })
diff --git a/test/req.route.js b/test/req.route.js
index 9bd7ed923b4..c7dbd7cf992 100644
--- a/test/req.route.js
+++ b/test/req.route.js
@@ -1,22 +1,22 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.route', function(){
-    it('should be the executed Route', function(done){
-      var app = express();
+describe('req', () => {
+  describe('.route', () => {
+    it('should be the executed Route', (done) => {
+      const app = express()
 
-      app.get('/user/:id{/:op}', function(req, res, next){
+      app.get('/user/:id{/:op}', (req, res, next) => {
         res.header('path-1', req.route.path)
-        next();
-      });
+        next()
+      })
 
-      app.get('/user/:id/edit', function(req, res){
+      app.get('/user/:id/edit', (req, res) => {
         res.header('path-2', req.route.path)
-        res.end();
-      });
+        res.end()
+      })
 
       request(app)
         .get('/user/12/edit')
diff --git a/test/req.secure.js b/test/req.secure.js
index 0097ed6136e..c8393b65725 100644
--- a/test/req.secure.js
+++ b/test/req.secure.js
@@ -1,99 +1,99 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.secure', function(){
-    describe('when X-Forwarded-Proto is missing', function(){
-      it('should return false when http', function(done){
-        var app = express();
+describe('req', () => {
+  describe('.secure', () => {
+    describe('when X-Forwarded-Proto is missing', () => {
+      it('should return false when http', (done) => {
+        const app = express()
 
-        app.get('/', function(req, res){
-          res.send(req.secure ? 'yes' : 'no');
-        });
+        app.get('/', (req, res) => {
+          res.send(req.secure ? 'yes' : 'no')
+        })
 
         request(app)
-        .get('/')
-        .expect('no', done)
+          .get('/')
+          .expect('no', done)
       })
     })
   })
 
-  describe('.secure', function(){
-    describe('when X-Forwarded-Proto is present', function(){
-      it('should return false when http', function(done){
-        var app = express();
+  describe('.secure', () => {
+    describe('when X-Forwarded-Proto is present', () => {
+      it('should return false when http', (done) => {
+        const app = express()
 
-        app.get('/', function(req, res){
-          res.send(req.secure ? 'yes' : 'no');
-        });
+        app.get('/', (req, res) => {
+          res.send(req.secure ? 'yes' : 'no')
+        })
 
         request(app)
-        .get('/')
-        .set('X-Forwarded-Proto', 'https')
-        .expect('no', done)
+          .get('/')
+          .set('X-Forwarded-Proto', 'https')
+          .expect('no', done)
       })
 
-      it('should return true when "trust proxy" is enabled', function(done){
-        var app = express();
+      it('should return true when "trust proxy" is enabled', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.get('/', function(req, res){
-          res.send(req.secure ? 'yes' : 'no');
-        });
+        app.get('/', (req, res) => {
+          res.send(req.secure ? 'yes' : 'no')
+        })
 
         request(app)
-        .get('/')
-        .set('X-Forwarded-Proto', 'https')
-        .expect('yes', done)
+          .get('/')
+          .set('X-Forwarded-Proto', 'https')
+          .expect('yes', done)
       })
 
-      it('should return false when initial proxy is http', function(done){
-        var app = express();
+      it('should return false when initial proxy is http', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.get('/', function(req, res){
-          res.send(req.secure ? 'yes' : 'no');
-        });
+        app.get('/', (req, res) => {
+          res.send(req.secure ? 'yes' : 'no')
+        })
 
         request(app)
-        .get('/')
-        .set('X-Forwarded-Proto', 'http, https')
-        .expect('no', done)
+          .get('/')
+          .set('X-Forwarded-Proto', 'http, https')
+          .expect('no', done)
       })
 
-      it('should return true when initial proxy is https', function(done){
-        var app = express();
+      it('should return true when initial proxy is https', (done) => {
+        const app = express()
 
-        app.enable('trust proxy');
+        app.enable('trust proxy')
 
-        app.get('/', function(req, res){
-          res.send(req.secure ? 'yes' : 'no');
-        });
+        app.get('/', (req, res) => {
+          res.send(req.secure ? 'yes' : 'no')
+        })
 
         request(app)
-        .get('/')
-        .set('X-Forwarded-Proto', 'https, http')
-        .expect('yes', done)
+          .get('/')
+          .set('X-Forwarded-Proto', 'https, http')
+          .expect('yes', done)
       })
 
-      describe('when "trust proxy" trusting hop count', function () {
-        it('should respect X-Forwarded-Proto', function (done) {
-          var app = express();
+      describe('when "trust proxy" trusting hop count', () => {
+        it('should respect X-Forwarded-Proto', (done) => {
+          const app = express()
 
-          app.set('trust proxy', 1);
+          app.set('trust proxy', 1)
 
-          app.get('/', function (req, res) {
-            res.send(req.secure ? 'yes' : 'no');
-          });
+          app.get('/', (req, res) => {
+            res.send(req.secure ? 'yes' : 'no')
+          })
 
           request(app)
-          .get('/')
-          .set('X-Forwarded-Proto', 'https')
-          .expect('yes', done)
+            .get('/')
+            .set('X-Forwarded-Proto', 'https')
+            .expect('yes', done)
         })
       })
     })
diff --git a/test/req.signedCookies.js b/test/req.signedCookies.js
index db561951665..529dd324901 100644
--- a/test/req.signedCookies.js
+++ b/test/req.signedCookies.js
@@ -1,37 +1,36 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest')
-  , cookieParser = require('cookie-parser')
+const express = require('../')
+const request = require('supertest')
+const cookieParser = require('cookie-parser')
 
-describe('req', function(){
-  describe('.signedCookies', function(){
-    it('should return a signed JSON cookie', function(done){
-      var app = express();
+describe('req', () => {
+  describe('.signedCookies', () => {
+    it('should return a signed JSON cookie', (done) => {
+      const app = express()
 
-      app.use(cookieParser('secret'));
+      app.use(cookieParser('secret'))
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         if (req.path === '/set') {
-          res.cookie('obj', { foo: 'bar' }, { signed: true });
-          res.end();
+          res.cookie('obj', { foo: 'bar' }, { signed: true })
+          res.end()
         } else {
-          res.send(req.signedCookies);
+          res.send(req.signedCookies)
         }
-      });
+      })
 
       request(app)
-      .get('/set')
-      .end(function(err, res){
-        if (err) return done(err);
-        var cookie = res.header['set-cookie'];
+        .get('/set')
+        .end((err, res) => {
+          if (err) return done(err)
+          const cookie = res.header['set-cookie']
 
-        request(app)
-        .get('/')
-        .set('Cookie', cookie)
-        .expect(200, { obj: { foo: 'bar' } }, done)
-      });
+          request(app)
+            .get('/')
+            .set('Cookie', cookie)
+            .expect(200, { obj: { foo: 'bar' } }, done)
+        })
     })
   })
 })
-
diff --git a/test/req.stale.js b/test/req.stale.js
index cda77fa403e..7217121ed4c 100644
--- a/test/req.stale.js
+++ b/test/req.stale.js
@@ -1,50 +1,50 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.stale', function(){
-    it('should return false when the resource is not modified', function(done){
-      var app = express();
-      var etag = '"12345"';
+describe('req', () => {
+  describe('.stale', () => {
+    it('should return false when the resource is not modified', (done) => {
+      const app = express()
+      const etag = '"12345"'
 
-      app.use(function(req, res){
-        res.set('ETag', etag);
-        res.send(req.stale);
-      });
+      app.use((req, res) => {
+        res.set('ETag', etag)
+        res.send(req.stale)
+      })
 
       request(app)
-      .get('/')
-      .set('If-None-Match', etag)
-      .expect(304, done);
+        .get('/')
+        .set('If-None-Match', etag)
+        .expect(304, done)
     })
 
-    it('should return true when the resource is modified', function(done){
-      var app = express();
+    it('should return true when the resource is modified', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.set('ETag', '"123"');
-        res.send(req.stale);
-      });
+      app.use((req, res) => {
+        res.set('ETag', '"123"')
+        res.send(req.stale)
+      })
 
       request(app)
-      .get('/')
-      .set('If-None-Match', '"12345"')
-      .expect(200, 'true', done);
+        .get('/')
+        .set('If-None-Match', '"12345"')
+        .expect(200, 'true', done)
     })
 
-    it('should return true without response headers', function(done){
-      var app = express();
+    it('should return true without response headers', (done) => {
+      const app = express()
 
       app.disable('x-powered-by')
-      app.use(function(req, res){
-        res.send(req.stale);
-      });
+      app.use((req, res) => {
+        res.send(req.stale)
+      })
 
       request(app)
-      .get('/')
-      .expect(200, 'true', done);
+        .get('/')
+        .expect(200, 'true', done)
     })
   })
 })
diff --git a/test/req.subdomains.js b/test/req.subdomains.js
index e5600f2eb56..01230b4e831 100644
--- a/test/req.subdomains.js
+++ b/test/req.subdomains.js
@@ -1,171 +1,171 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.subdomains', function(){
-    describe('when present', function(){
-      it('should return an array', function(done){
-        var app = express();
+describe('req', () => {
+  describe('.subdomains', () => {
+    describe('when present', () => {
+      it('should return an array', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.send(req.subdomains);
-        });
+        app.use((req, res) => {
+          res.send(req.subdomains)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'tobi.ferrets.example.com')
-        .expect(200, ['ferrets', 'tobi'], done);
+          .get('/')
+          .set('Host', 'tobi.ferrets.example.com')
+          .expect(200, ['ferrets', 'tobi'], done)
       })
 
-      it('should work with IPv4 address', function(done){
-        var app = express();
+      it('should work with IPv4 address', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.send(req.subdomains);
-        });
+        app.use((req, res) => {
+          res.send(req.subdomains)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', '127.0.0.1')
-        .expect(200, [], done);
+          .get('/')
+          .set('Host', '127.0.0.1')
+          .expect(200, [], done)
       })
 
-      it('should work with IPv6 address', function(done){
-        var app = express();
+      it('should work with IPv6 address', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.send(req.subdomains);
-        });
+        app.use((req, res) => {
+          res.send(req.subdomains)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', '[::1]')
-        .expect(200, [], done);
+          .get('/')
+          .set('Host', '[::1]')
+          .expect(200, [], done)
       })
     })
 
-    describe('otherwise', function(){
-      it('should return an empty array', function(done){
-        var app = express();
+    describe('otherwise', () => {
+      it('should return an empty array', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.send(req.subdomains);
-        });
+        app.use((req, res) => {
+          res.send(req.subdomains)
+        })
 
         request(app)
-        .get('/')
-        .set('Host', 'example.com')
-        .expect(200, [], done);
+          .get('/')
+          .set('Host', 'example.com')
+          .expect(200, [], done)
       })
     })
 
-    describe('with no host', function(){
-      it('should return an empty array', function(done){
-        var app = express();
+    describe('with no host', () => {
+      it('should return an empty array', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          req.headers.host = null;
-          res.send(req.subdomains);
-        });
+        app.use((req, res) => {
+          req.headers.host = null
+          res.send(req.subdomains)
+        })
 
         request(app)
-        .get('/')
-        .expect(200, [], done);
+          .get('/')
+          .expect(200, [], done)
       })
     })
 
-    describe('with trusted X-Forwarded-Host', function () {
-      it('should return an array', function (done) {
-        var app = express();
+    describe('with trusted X-Forwarded-Host', () => {
+      it('should return an array', (done) => {
+        const app = express()
 
-        app.set('trust proxy', true);
-        app.use(function (req, res) {
-          res.send(req.subdomains);
-        });
+        app.set('trust proxy', true)
+        app.use((req, res) => {
+          res.send(req.subdomains)
+        })
 
         request(app)
-        .get('/')
-        .set('X-Forwarded-Host', 'tobi.ferrets.example.com')
-        .expect(200, ['ferrets', 'tobi'], done);
+          .get('/')
+          .set('X-Forwarded-Host', 'tobi.ferrets.example.com')
+          .expect(200, ['ferrets', 'tobi'], done)
       })
     })
 
-    describe('when subdomain offset is set', function(){
-      describe('when subdomain offset is zero', function(){
-        it('should return an array with the whole domain', function(done){
-          var app = express();
-          app.set('subdomain offset', 0);
+    describe('when subdomain offset is set', () => {
+      describe('when subdomain offset is zero', () => {
+        it('should return an array with the whole domain', (done) => {
+          const app = express()
+          app.set('subdomain offset', 0)
 
-          app.use(function(req, res){
-            res.send(req.subdomains);
-          });
+          app.use((req, res) => {
+            res.send(req.subdomains)
+          })
 
           request(app)
-          .get('/')
-          .set('Host', 'tobi.ferrets.sub.example.com')
-          .expect(200, ['com', 'example', 'sub', 'ferrets', 'tobi'], done);
+            .get('/')
+            .set('Host', 'tobi.ferrets.sub.example.com')
+            .expect(200, ['com', 'example', 'sub', 'ferrets', 'tobi'], done)
         })
 
-        it('should return an array with the whole IPv4', function (done) {
-          var app = express();
-          app.set('subdomain offset', 0);
+        it('should return an array with the whole IPv4', (done) => {
+          const app = express()
+          app.set('subdomain offset', 0)
 
-          app.use(function(req, res){
-            res.send(req.subdomains);
-          });
+          app.use((req, res) => {
+            res.send(req.subdomains)
+          })
 
           request(app)
-          .get('/')
-          .set('Host', '127.0.0.1')
-          .expect(200, ['127.0.0.1'], done);
+            .get('/')
+            .set('Host', '127.0.0.1')
+            .expect(200, ['127.0.0.1'], done)
         })
 
-        it('should return an array with the whole IPv6', function (done) {
-          var app = express();
-          app.set('subdomain offset', 0);
+        it('should return an array with the whole IPv6', (done) => {
+          const app = express()
+          app.set('subdomain offset', 0)
 
-          app.use(function(req, res){
-            res.send(req.subdomains);
-          });
+          app.use((req, res) => {
+            res.send(req.subdomains)
+          })
 
           request(app)
-          .get('/')
-          .set('Host', '[::1]')
-          .expect(200, ['[::1]'], done);
+            .get('/')
+            .set('Host', '[::1]')
+            .expect(200, ['[::1]'], done)
         })
       })
 
-      describe('when present', function(){
-        it('should return an array', function(done){
-          var app = express();
-          app.set('subdomain offset', 3);
+      describe('when present', () => {
+        it('should return an array', (done) => {
+          const app = express()
+          app.set('subdomain offset', 3)
 
-          app.use(function(req, res){
-            res.send(req.subdomains);
-          });
+          app.use((req, res) => {
+            res.send(req.subdomains)
+          })
 
           request(app)
-          .get('/')
-          .set('Host', 'tobi.ferrets.sub.example.com')
-          .expect(200, ['ferrets', 'tobi'], done);
+            .get('/')
+            .set('Host', 'tobi.ferrets.sub.example.com')
+            .expect(200, ['ferrets', 'tobi'], done)
         })
       })
 
-      describe('otherwise', function(){
-        it('should return an empty array', function(done){
-          var app = express();
-          app.set('subdomain offset', 3);
+      describe('otherwise', () => {
+        it('should return an empty array', (done) => {
+          const app = express()
+          app.set('subdomain offset', 3)
 
-          app.use(function(req, res){
-            res.send(req.subdomains);
-          });
+          app.use((req, res) => {
+            res.send(req.subdomains)
+          })
 
           request(app)
-          .get('/')
-          .set('Host', 'sub.example.com')
-          .expect(200, [], done);
+            .get('/')
+            .set('Host', 'sub.example.com')
+            .expect(200, [], done)
         })
       })
     })
diff --git a/test/req.xhr.js b/test/req.xhr.js
index 99cf7f1917d..629f134230d 100644
--- a/test/req.xhr.js
+++ b/test/req.xhr.js
@@ -1,39 +1,39 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('req', function(){
-  describe('.xhr', function(){
+describe('req', () => {
+  describe('.xhr', () => {
     before(function () {
       this.app = express()
-      this.app.get('/', function (req, res) {
+      this.app.get('/', (req, res) => {
         res.send(req.xhr)
       })
     })
 
-    it('should return true when X-Requested-With is xmlhttprequest', function(done){
+    it('should return true when X-Requested-With is xmlhttprequest', function (done) {
       request(this.app)
         .get('/')
         .set('X-Requested-With', 'xmlhttprequest')
         .expect(200, 'true', done)
     })
 
-    it('should case-insensitive', function(done){
+    it('should case-insensitive', function (done) {
       request(this.app)
         .get('/')
         .set('X-Requested-With', 'XMLHttpRequest')
         .expect(200, 'true', done)
     })
 
-    it('should return false otherwise', function(done){
+    it('should return false otherwise', function (done) {
       request(this.app)
         .get('/')
         .set('X-Requested-With', 'blahblah')
         .expect(200, 'false', done)
     })
 
-    it('should return false when not present', function(done){
+    it('should return false when not present', function (done) {
       request(this.app)
         .get('/')
         .expect(200, 'false', done)
diff --git a/test/res.append.js b/test/res.append.js
index 2dd17a3a1fb..154c72f6c17 100644
--- a/test/res.append.js
+++ b/test/res.append.js
@@ -1,20 +1,20 @@
 'use strict'
 
-var assert = require('node:assert')
-var express = require('..')
-var request = require('supertest')
+const assert = require('node:assert')
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function () {
-  describe('.append(field, val)', function () {
-    it('should append multiple headers', function (done) {
-      var app = express()
+describe('res', () => {
+  describe('.append(field, val)', () => {
+    it('should append multiple headers', (done) => {
+      const app = express()
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         res.append('Set-Cookie', 'foo=bar')
         next()
       })
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.append('Set-Cookie', 'fizz=buzz')
         res.end()
       })
@@ -26,10 +26,10 @@ describe('res', function () {
         .end(done)
     })
 
-    it('should accept array of values', function (done) {
-      var app = express()
+    it('should accept array of values', (done) => {
+      const app = express()
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         res.append('Set-Cookie', ['foo=bar', 'fizz=buzz'])
         res.end()
       })
@@ -41,19 +41,19 @@ describe('res', function () {
         .end(done)
     })
 
-    it('should get reset by res.set(field, val)', function (done) {
-      var app = express()
+    it('should get reset by res.set(field, val)', (done) => {
+      const app = express()
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         res.append('Set-Cookie', 'foo=bar')
         res.append('Set-Cookie', 'fizz=buzz')
         next()
       })
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.set('Set-Cookie', 'pet=tobi')
         res.end()
-      });
+      })
 
       request(app)
         .get('/')
@@ -62,15 +62,15 @@ describe('res', function () {
         .end(done)
     })
 
-    it('should work with res.set(field, val) first', function (done) {
-      var app = express()
+    it('should work with res.set(field, val) first', (done) => {
+      const app = express()
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         res.set('Set-Cookie', 'foo=bar')
         next()
       })
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.append('Set-Cookie', 'fizz=buzz')
         res.end()
       })
@@ -82,15 +82,15 @@ describe('res', function () {
         .end(done)
     })
 
-    it('should work together with res.cookie', function (done) {
-      var app = express()
+    it('should work together with res.cookie', (done) => {
+      const app = express()
 
-      app.use(function (req, res, next) {
+      app.use((req, res, next) => {
         res.cookie('foo', 'bar')
         next()
       })
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.append('Set-Cookie', 'fizz=buzz')
         res.end()
       })
@@ -106,10 +106,10 @@ describe('res', function () {
 
 function shouldHaveHeaderValues (key, values) {
   return function (res) {
-    var headers = res.headers[key.toLowerCase()]
+    const headers = res.headers[key.toLowerCase()]
     assert.ok(headers, 'should have header "' + key + '"')
     assert.strictEqual(headers.length, values.length, 'should have ' + values.length + ' occurrences of "' + key + '"')
-    for (var i = 0; i < values.length; i++) {
+    for (let i = 0; i < values.length; i++) {
       assert.strictEqual(headers[i], values[i])
     }
   }
diff --git a/test/res.attachment.js b/test/res.attachment.js
index 8644bab5b2d..686a9874cac 100644
--- a/test/res.attachment.js
+++ b/test/res.attachment.js
@@ -1,79 +1,79 @@
 'use strict'
 
-const { Buffer } = require('node:buffer');
+const { Buffer } = require('node:buffer')
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function(){
-  describe('.attachment()', function(){
-    it('should Content-Disposition to attachment', function(done){
-      var app = express();
+describe('res', () => {
+  describe('.attachment()', () => {
+    it('should Content-Disposition to attachment', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.attachment().send('foo');
-      });
+      app.use((req, res) => {
+        res.attachment().send('foo')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Disposition', 'attachment', done);
+        .get('/')
+        .expect('Content-Disposition', 'attachment', done)
     })
   })
 
-  describe('.attachment(filename)', function(){
-    it('should add the filename param', function(done){
-      var app = express();
+  describe('.attachment(filename)', () => {
+    it('should add the filename param', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.attachment('/path/to/image.png');
-        res.send('foo');
-      });
+      app.use((req, res) => {
+        res.attachment('/path/to/image.png')
+        res.send('foo')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Disposition', 'attachment; filename="image.png"', done);
+        .get('/')
+        .expect('Content-Disposition', 'attachment; filename="image.png"', done)
     })
 
-    it('should set the Content-Type', function(done){
-      var app = express();
+    it('should set the Content-Type', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.attachment('/path/to/image.png');
+      app.use((req, res) => {
+        res.attachment('/path/to/image.png')
         res.send(Buffer.alloc(4, '.'))
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'image/png', done);
+        .get('/')
+        .expect('Content-Type', 'image/png', done)
     })
   })
 
-  describe('.attachment(utf8filename)', function(){
-    it('should add the filename and filename* params', function(done){
-      var app = express();
+  describe('.attachment(utf8filename)', () => {
+    it('should add the filename and filename* params', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.attachment('/locales/日本語.txt');
-        res.send('japanese');
-      });
+      app.use((req, res) => {
+        res.attachment('/locales/日本語.txt')
+        res.send('japanese')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Disposition', 'attachment; filename="???.txt"; filename*=UTF-8\'\'%E6%97%A5%E6%9C%AC%E8%AA%9E.txt')
-      .expect(200, done);
+        .get('/')
+        .expect('Content-Disposition', 'attachment; filename="???.txt"; filename*=UTF-8\'\'%E6%97%A5%E6%9C%AC%E8%AA%9E.txt')
+        .expect(200, done)
     })
 
-    it('should set the Content-Type', function(done){
-      var app = express();
+    it('should set the Content-Type', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.attachment('/locales/日本語.txt');
-        res.send('japanese');
-      });
+      app.use((req, res) => {
+        res.attachment('/locales/日本語.txt')
+        res.send('japanese')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/plain; charset=utf-8', done);
+        .get('/')
+        .expect('Content-Type', 'text/plain; charset=utf-8', done)
     })
   })
 })
diff --git a/test/res.clearCookie.js b/test/res.clearCookie.js
index 74a746eb7be..4af1a8e1ebc 100644
--- a/test/res.clearCookie.js
+++ b/test/res.clearCookie.js
@@ -1,62 +1,62 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function(){
-  describe('.clearCookie(name)', function(){
-    it('should set a cookie passed expiry', function(done){
-      var app = express();
+describe('res', () => {
+  describe('.clearCookie(name)', () => {
+    it('should set a cookie passed expiry', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.clearCookie('sid').end();
-      });
+      app.use((req, res) => {
+        res.clearCookie('sid').end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Set-Cookie', 'sid=; Path=/; Expires=Thu, 01 Jan 1970 00:00:00 GMT')
-      .expect(200, done)
+        .get('/')
+        .expect('Set-Cookie', 'sid=; Path=/; Expires=Thu, 01 Jan 1970 00:00:00 GMT')
+        .expect(200, done)
     })
   })
 
-  describe('.clearCookie(name, options)', function(){
-    it('should set the given params', function(done){
-      var app = express();
+  describe('.clearCookie(name, options)', () => {
+    it('should set the given params', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.clearCookie('sid', { path: '/admin' }).end();
-      });
+      app.use((req, res) => {
+        res.clearCookie('sid', { path: '/admin' }).end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Set-Cookie', 'sid=; Path=/admin; Expires=Thu, 01 Jan 1970 00:00:00 GMT')
-      .expect(200, done)
+        .get('/')
+        .expect('Set-Cookie', 'sid=; Path=/admin; Expires=Thu, 01 Jan 1970 00:00:00 GMT')
+        .expect(200, done)
     })
 
-    it('should ignore maxAge', function(done){
-      var app = express();
+    it('should ignore maxAge', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.clearCookie('sid', { path: '/admin', maxAge: 1000 }).end();
-      });
+      app.use((req, res) => {
+        res.clearCookie('sid', { path: '/admin', maxAge: 1000 }).end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Set-Cookie', 'sid=; Path=/admin; Expires=Thu, 01 Jan 1970 00:00:00 GMT')
-      .expect(200, done)
+        .get('/')
+        .expect('Set-Cookie', 'sid=; Path=/admin; Expires=Thu, 01 Jan 1970 00:00:00 GMT')
+        .expect(200, done)
     })
 
-    it('should ignore user supplied expires param', function(done){
-      var app = express();
+    it('should ignore user supplied expires param', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.clearCookie('sid', { path: '/admin', expires: new Date() }).end();
-      });
+      app.use((req, res) => {
+        res.clearCookie('sid', { path: '/admin', expires: new Date() }).end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Set-Cookie', 'sid=; Path=/admin; Expires=Thu, 01 Jan 1970 00:00:00 GMT')
-      .expect(200, done)
+        .get('/')
+        .expect('Set-Cookie', 'sid=; Path=/admin; Expires=Thu, 01 Jan 1970 00:00:00 GMT')
+        .expect(200, done)
     })
   })
 })
diff --git a/test/res.cookie.js b/test/res.cookie.js
index 180d1be3452..9a0a40fae17 100644
--- a/test/res.cookie.js
+++ b/test/res.cookie.js
@@ -1,48 +1,48 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest')
-  , cookieParser = require('cookie-parser')
+const express = require('../')
+const request = require('supertest')
+const cookieParser = require('cookie-parser')
 
-describe('res', function(){
-  describe('.cookie(name, object)', function(){
-    it('should generate a JSON cookie', function(done){
-      var app = express();
+describe('res', () => {
+  describe('.cookie(name, object)', () => {
+    it('should generate a JSON cookie', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.cookie('user', { name: 'tobi' }).end();
-      });
+      app.use((req, res) => {
+        res.cookie('user', { name: 'tobi' }).end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Set-Cookie', 'user=j%3A%7B%22name%22%3A%22tobi%22%7D; Path=/')
-      .expect(200, done)
+        .get('/')
+        .expect('Set-Cookie', 'user=j%3A%7B%22name%22%3A%22tobi%22%7D; Path=/')
+        .expect(200, done)
     })
   })
 
-  describe('.cookie(name, string)', function(){
-    it('should set a cookie', function(done){
-      var app = express();
+  describe('.cookie(name, string)', () => {
+    it('should set a cookie', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.cookie('name', 'tobi').end();
-      });
+      app.use((req, res) => {
+        res.cookie('name', 'tobi').end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Set-Cookie', 'name=tobi; Path=/')
-      .expect(200, done)
+        .get('/')
+        .expect('Set-Cookie', 'name=tobi; Path=/')
+        .expect(200, done)
     })
 
-    it('should allow multiple calls', function(done){
-      var app = express();
+    it('should allow multiple calls', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.cookie('name', 'tobi');
-        res.cookie('age', 1);
-        res.cookie('gender', '?');
-        res.end();
-      });
+      app.use((req, res) => {
+        res.cookie('name', 'tobi')
+        res.cookie('age', 1)
+        res.cookie('gender', '?')
+        res.end()
+      })
 
       request(app)
         .get('/')
@@ -51,26 +51,26 @@ describe('res', function(){
     })
   })
 
-  describe('.cookie(name, string, options)', function(){
-    it('should set params', function(done){
-      var app = express();
+  describe('.cookie(name, string, options)', () => {
+    it('should set params', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.cookie('name', 'tobi', { httpOnly: true, secure: true });
-        res.end();
-      });
+      app.use((req, res) => {
+        res.cookie('name', 'tobi', { httpOnly: true, secure: true })
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Set-Cookie', 'name=tobi; Path=/; HttpOnly; Secure')
-      .expect(200, done)
+        .get('/')
+        .expect('Set-Cookie', 'name=tobi; Path=/; HttpOnly; Secure')
+        .expect(200, done)
     })
 
-    describe('expires', function () {
-      it('should throw on invalid date', function (done) {
-        var app = express()
+    describe('expires', () => {
+      it('should throw on invalid date', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.cookie('name', 'tobi', { expires: new Date(NaN) })
           res.end()
         })
@@ -81,14 +81,14 @@ describe('res', function(){
       })
     })
 
-    describe('partitioned', function () {
-      it('should set partitioned', function (done) {
-        var app = express();
+    describe('partitioned', () => {
+      it('should set partitioned', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.cookie('name', 'tobi', { partitioned: true });
-          res.end();
-        });
+        app.use((req, res) => {
+          res.cookie('name', 'tobi', { partitioned: true })
+          res.end()
+        })
 
         request(app)
           .get('/')
@@ -97,14 +97,14 @@ describe('res', function(){
       })
     })
 
-    describe('maxAge', function(){
-      it('should set relative expires', function(done){
-        var app = express();
+    describe('maxAge', () => {
+      it('should set relative expires', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.cookie('name', 'tobi', { maxAge: 1000 });
-          res.end();
-        });
+        app.use((req, res) => {
+          res.cookie('name', 'tobi', { maxAge: 1000 })
+          res.end()
+        })
 
         request(app)
           .get('/')
@@ -112,39 +112,39 @@ describe('res', function(){
           .expect(200, done)
       })
 
-      it('should set max-age', function(done){
-        var app = express();
+      it('should set max-age', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.cookie('name', 'tobi', { maxAge: 1000 });
-          res.end();
-        });
+        app.use((req, res) => {
+          res.cookie('name', 'tobi', { maxAge: 1000 })
+          res.end()
+        })
 
         request(app)
-        .get('/')
-        .expect('Set-Cookie', /Max-Age=1/, done)
+          .get('/')
+          .expect('Set-Cookie', /Max-Age=1/, done)
       })
 
-      it('should not mutate the options object', function(done){
-        var app = express();
+      it('should not mutate the options object', (done) => {
+        const app = express()
 
-        var options = { maxAge: 1000 };
-        var optionsCopy = { ...options };
+        const options = { maxAge: 1000 }
+        const optionsCopy = { ...options }
 
-        app.use(function(req, res){
+        app.use((req, res) => {
           res.cookie('name', 'tobi', options)
           res.json(options)
-        });
+        })
 
         request(app)
-        .get('/')
-        .expect(200, optionsCopy, done)
+          .get('/')
+          .expect(200, optionsCopy, done)
       })
 
-      it('should not throw on null', function (done) {
-        var app = express()
+      it('should not throw on null', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.cookie('name', 'tobi', { maxAge: null })
           res.end()
         })
@@ -156,10 +156,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should not throw on undefined', function (done) {
-        var app = express()
+      it('should not throw on undefined', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.cookie('name', 'tobi', { maxAge: undefined })
           res.end()
         })
@@ -171,10 +171,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should throw an error with invalid maxAge', function (done) {
-        var app = express()
+      it('should throw an error with invalid maxAge', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.cookie('name', 'tobi', { maxAge: 'foobar' })
           res.end()
         })
@@ -185,11 +185,11 @@ describe('res', function(){
       })
     })
 
-    describe('priority', function () {
-      it('should set low priority', function (done) {
-        var app = express()
+    describe('priority', () => {
+      it('should set low priority', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.cookie('name', 'tobi', { priority: 'low' })
           res.end()
         })
@@ -200,10 +200,10 @@ describe('res', function(){
           .expect(200, done)
       })
 
-      it('should set medium priority', function (done) {
-        var app = express()
+      it('should set medium priority', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.cookie('name', 'tobi', { priority: 'medium' })
           res.end()
         })
@@ -214,10 +214,10 @@ describe('res', function(){
           .expect(200, done)
       })
 
-      it('should set high priority', function (done) {
-        var app = express()
+      it('should set high priority', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.cookie('name', 'tobi', { priority: 'high' })
           res.end()
         })
@@ -228,10 +228,10 @@ describe('res', function(){
           .expect(200, done)
       })
 
-      it('should throw with invalid priority', function (done) {
-        var app = express()
+      it('should throw with invalid priority', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.cookie('name', 'tobi', { priority: 'foobar' })
           res.end()
         })
@@ -242,15 +242,15 @@ describe('res', function(){
       })
     })
 
-    describe('signed', function(){
-      it('should generate a signed JSON cookie', function(done){
-        var app = express();
+    describe('signed', () => {
+      it('should generate a signed JSON cookie', (done) => {
+        const app = express()
 
-        app.use(cookieParser('foo bar baz'));
+        app.use(cookieParser('foo bar baz'))
 
-        app.use(function(req, res){
-          res.cookie('user', { name: 'tobi' }, { signed: true }).end();
-        });
+        app.use((req, res) => {
+          res.cookie('user', { name: 'tobi' }, { signed: true }).end()
+        })
 
         request(app)
           .get('/')
@@ -259,36 +259,36 @@ describe('res', function(){
       })
     })
 
-    describe('signed without secret', function(){
-      it('should throw an error', function(done){
-        var app = express();
+    describe('signed without secret', () => {
+      it('should throw an error', (done) => {
+        const app = express()
 
-        app.use(cookieParser());
+        app.use(cookieParser())
 
-        app.use(function(req, res){
-          res.cookie('name', 'tobi', { signed: true }).end();
-        });
+        app.use((req, res) => {
+          res.cookie('name', 'tobi', { signed: true }).end()
+        })
 
         request(app)
-        .get('/')
-        .expect(500, /secret\S+ required for signed cookies/, done);
+          .get('/')
+          .expect(500, /secret\S+ required for signed cookies/, done)
       })
     })
 
-    describe('.signedCookie(name, string)', function(){
-      it('should set a signed cookie', function(done){
-        var app = express();
+    describe('.signedCookie(name, string)', () => {
+      it('should set a signed cookie', (done) => {
+        const app = express()
 
-        app.use(cookieParser('foo bar baz'));
+        app.use(cookieParser('foo bar baz'))
 
-        app.use(function(req, res){
-          res.cookie('name', 'tobi', { signed: true }).end();
-        });
+        app.use((req, res) => {
+          res.cookie('name', 'tobi', { signed: true }).end()
+        })
 
         request(app)
-        .get('/')
-        .expect('Set-Cookie', 'name=s%3Atobi.xJjV2iZ6EI7C8E5kzwbfA9PVLl1ZR07UTnuTgQQ4EnQ; Path=/')
-        .expect(200, done)
+          .get('/')
+          .expect('Set-Cookie', 'name=s%3Atobi.xJjV2iZ6EI7C8E5kzwbfA9PVLl1ZR07UTnuTgQQ4EnQ; Path=/')
+          .expect(200, done)
       })
     })
   })
diff --git a/test/res.download.js b/test/res.download.js
index e9966007eba..f664529f568 100644
--- a/test/res.download.js
+++ b/test/res.download.js
@@ -1,37 +1,37 @@
 'use strict'
 
-var after = require('after');
-var assert = require('node:assert')
-var AsyncLocalStorage = require('node:async_hooks').AsyncLocalStorage
-const { Buffer } = require('node:buffer');
+const after = require('after')
+const assert = require('node:assert')
+const { AsyncLocalStorage } = require('node:async_hooks')
+const { Buffer } = require('node:buffer')
 
-var express = require('..');
-var path = require('node:path')
-var request = require('supertest');
-var utils = require('./support/utils')
+const express = require('../')
+const path = require('node:path')
+const request = require('supertest')
+const utils = require('./support/utils')
 
-var FIXTURES_PATH = path.join(__dirname, 'fixtures')
+const FIXTURES_PATH = path.join(__dirname, 'fixtures')
 
-describe('res', function(){
-  describe('.download(path)', function(){
-    it('should transfer as an attachment', function(done){
-      var app = express();
+describe('res', () => {
+  describe('.download(path)', () => {
+    it('should transfer as an attachment', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.download('test/fixtures/user.html');
-      });
+      app.use((req, res) => {
+        res.download('test/fixtures/user.html')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/html; charset=utf-8')
-      .expect('Content-Disposition', 'attachment; filename="user.html"')
-      .expect(200, '<p>{{user.name}}</p>', done)
+        .get('/')
+        .expect('Content-Type', 'text/html; charset=utf-8')
+        .expect('Content-Disposition', 'attachment; filename="user.html"')
+        .expect(200, '<p>{{user.name}}</p>', done)
     })
 
-    it('should accept range requests', function (done) {
-      var app = express()
+    it('should accept range requests', (done) => {
+      const app = express()
 
-      app.get('/', function (req, res) {
+      app.get('/', (req, res) => {
         res.download('test/fixtures/user.html')
       })
 
@@ -41,10 +41,10 @@ describe('res', function(){
         .expect(200, '<p>{{user.name}}</p>', done)
     })
 
-    it('should respond with requested byte range', function (done) {
-      var app = express()
+    it('should respond with requested byte range', (done) => {
+      const app = express()
 
-      app.get('/', function (req, res) {
+      app.get('/', (req, res) => {
         res.download('test/fixtures/user.html')
       })
 
@@ -56,54 +56,54 @@ describe('res', function(){
     })
   })
 
-  describe('.download(path, filename)', function(){
-    it('should provide an alternate filename', function(done){
-      var app = express();
+  describe('.download(path, filename)', () => {
+    it('should provide an alternate filename', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.download('test/fixtures/user.html', 'document');
-      });
+      app.use((req, res) => {
+        res.download('test/fixtures/user.html', 'document')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/html; charset=utf-8')
-      .expect('Content-Disposition', 'attachment; filename="document"')
-      .expect(200, done)
+        .get('/')
+        .expect('Content-Type', 'text/html; charset=utf-8')
+        .expect('Content-Disposition', 'attachment; filename="document"')
+        .expect(200, done)
     })
   })
 
-  describe('.download(path, fn)', function(){
-    it('should invoke the callback', function(done){
-      var app = express();
-      var cb = after(2, done);
+  describe('.download(path, fn)', () => {
+    it('should invoke the callback', (done) => {
+      const app = express()
+      const cb = after(2, done)
 
-      app.use(function(req, res){
-        res.download('test/fixtures/user.html', cb);
-      });
+      app.use((req, res) => {
+        res.download('test/fixtures/user.html', cb)
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/html; charset=utf-8')
-      .expect('Content-Disposition', 'attachment; filename="user.html"')
-      .expect(200, cb);
+        .get('/')
+        .expect('Content-Type', 'text/html; charset=utf-8')
+        .expect('Content-Disposition', 'attachment; filename="user.html"')
+        .expect(200, cb)
     })
 
-    describe('async local storage', function () {
-      it('should persist store', function (done) {
-        var app = express()
-        var cb = after(2, done)
-        var store = { foo: 'bar' }
+    describe('async local storage', () => {
+      it('should persist store', (done) => {
+        const app = express()
+        const cb = after(2, done)
+        const store = { foo: 'bar' }
 
-        app.use(function (req, res, next) {
+        app.use((req, res, next) => {
           req.asyncLocalStorage = new AsyncLocalStorage()
           req.asyncLocalStorage.run(store, next)
         })
 
-        app.use(function (req, res) {
-          res.download('test/fixtures/name.txt', function (err) {
+        app.use((req, res) => {
+          res.download('test/fixtures/name.txt', (err) => {
             if (err) return cb(err)
 
-            var local = req.asyncLocalStorage.getStore()
+            const local = req.asyncLocalStorage.getStore()
 
             assert.strictEqual(local.foo, 'bar')
             cb()
@@ -117,18 +117,18 @@ describe('res', function(){
           .expect(200, 'tobi', cb)
       })
 
-      it('should persist store on error', function (done) {
-        var app = express()
-        var store = { foo: 'bar' }
+      it('should persist store on error', (done) => {
+        const app = express()
+        const store = { foo: 'bar' }
 
-        app.use(function (req, res, next) {
+        app.use((req, res, next) => {
           req.asyncLocalStorage = new AsyncLocalStorage()
           req.asyncLocalStorage.run(store, next)
         })
 
-        app.use(function (req, res) {
-          res.download('test/fixtures/does-not-exist', function (err) {
-            var local = req.asyncLocalStorage.getStore()
+        app.use((req, res) => {
+          res.download('test/fixtures/does-not-exist', (err) => {
+            const local = req.asyncLocalStorage.getStore()
 
             if (local) {
               res.setHeader('x-store-foo', String(local.foo))
@@ -148,11 +148,11 @@ describe('res', function(){
     })
   })
 
-  describe('.download(path, options)', function () {
-    it('should allow options to res.sendFile()', function (done) {
-      var app = express()
+  describe('.download(path, options)', () => {
+    it('should allow options to res.sendFile()', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.download('test/fixtures/.name', {
           dotfiles: 'allow',
           maxAge: '4h'
@@ -168,11 +168,11 @@ describe('res', function(){
         .end(done)
     })
 
-    describe('with "headers" option', function () {
-      it('should set headers on response', function (done) {
-        var app = express()
+    describe('with "headers" option', () => {
+      it('should set headers on response', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.download('test/fixtures/user.html', {
             headers: {
               'X-Foo': 'Bar',
@@ -189,10 +189,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should use last header when duplicated', function (done) {
-        var app = express()
+      it('should use last header when duplicated', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.download('test/fixtures/user.html', {
             headers: {
               'X-Foo': 'Bar',
@@ -208,10 +208,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should override Content-Type', function (done) {
-        var app = express()
+      it('should override Content-Type', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.download('test/fixtures/user.html', {
             headers: {
               'Content-Type': 'text/x-custom'
@@ -226,10 +226,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should not set headers on 404', function (done) {
-        var app = express()
+      it('should not set headers on 404', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.download('test/fixtures/does-not-exist', {
             headers: {
               'X-Foo': 'Bar'
@@ -244,11 +244,11 @@ describe('res', function(){
           .end(done)
       })
 
-      describe('when headers contains Content-Disposition', function () {
-        it('should be ignored', function (done) {
-          var app = express()
+      describe('when headers contains Content-Disposition', () => {
+        it('should be ignored', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.download('test/fixtures/user.html', {
               headers: {
                 'Content-Disposition': 'inline'
@@ -263,10 +263,10 @@ describe('res', function(){
             .end(done)
         })
 
-        it('should be ignored case-insensitively', function (done) {
-          var app = express()
+        it('should be ignored case-insensitively', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.download('test/fixtures/user.html', {
               headers: {
                 'content-disposition': 'inline'
@@ -283,11 +283,11 @@ describe('res', function(){
       })
     })
 
-    describe('with "root" option', function () {
-      it('should allow relative path', function (done) {
-        var app = express()
+    describe('with "root" option', () => {
+      it('should allow relative path', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.download('name.txt', {
             root: FIXTURES_PATH
           })
@@ -301,10 +301,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should allow up within root', function (done) {
-        var app = express()
+      it('should allow up within root', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.download('fake/../name.txt', {
             root: FIXTURES_PATH
           })
@@ -318,11 +318,11 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should reject up outside root', function (done) {
-        var app = express()
+      it('should reject up outside root', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          var p = '..' + path.sep +
+        app.use((req, res) => {
+          const p = '..' + path.sep +
             path.relative(path.dirname(FIXTURES_PATH), path.join(FIXTURES_PATH, 'name.txt'))
 
           res.download(p, {
@@ -337,10 +337,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should reject reading outside root', function (done) {
-        var app = express()
+      it('should reject reading outside root', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.download('../name.txt', {
             root: FIXTURES_PATH
           })
@@ -355,45 +355,45 @@ describe('res', function(){
     })
   })
 
-  describe('.download(path, filename, fn)', function(){
-    it('should invoke the callback', function(done){
-      var app = express();
-      var cb = after(2, done);
+  describe('.download(path, filename, fn)', () => {
+    it('should invoke the callback', (done) => {
+      const app = express()
+      const cb = after(2, done)
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.download('test/fixtures/user.html', 'document', cb)
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/html; charset=utf-8')
-      .expect('Content-Disposition', 'attachment; filename="document"')
-      .expect(200, cb);
+        .get('/')
+        .expect('Content-Type', 'text/html; charset=utf-8')
+        .expect('Content-Disposition', 'attachment; filename="document"')
+        .expect(200, cb)
     })
   })
 
-  describe('.download(path, filename, options, fn)', function () {
-    it('should invoke the callback', function (done) {
-      var app = express()
-      var cb = after(2, done)
-      var options = {}
+  describe('.download(path, filename, options, fn)', () => {
+    it('should invoke the callback', (done) => {
+      const app = express()
+      const cb = after(2, done)
+      const options = {}
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.download('test/fixtures/user.html', 'document', options, cb)
       })
 
       request(app)
-      .get('/')
-      .expect(200)
-      .expect('Content-Type', 'text/html; charset=utf-8')
-      .expect('Content-Disposition', 'attachment; filename="document"')
-      .end(cb)
+        .get('/')
+        .expect(200)
+        .expect('Content-Type', 'text/html; charset=utf-8')
+        .expect('Content-Disposition', 'attachment; filename="document"')
+        .end(cb)
     })
 
-    it('should allow options to res.sendFile()', function (done) {
-      var app = express()
+    it('should allow options to res.sendFile()', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.download('test/fixtures/.name', 'document', {
           dotfiles: 'allow',
           maxAge: '4h'
@@ -409,11 +409,11 @@ describe('res', function(){
         .end(done)
     })
 
-    describe('when options.headers contains Content-Disposition', function () {
-      it('should be ignored', function (done) {
-        var app = express()
+    describe('when options.headers contains Content-Disposition', () => {
+      it('should be ignored', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.download('test/fixtures/user.html', 'document', {
             headers: {
               'Content-Type': 'text/x-custom',
@@ -423,17 +423,17 @@ describe('res', function(){
         })
 
         request(app)
-        .get('/')
-        .expect(200)
-        .expect('Content-Type', 'text/x-custom')
-        .expect('Content-Disposition', 'attachment; filename="document"')
-        .end(done)
+          .get('/')
+          .expect(200)
+          .expect('Content-Type', 'text/x-custom')
+          .expect('Content-Disposition', 'attachment; filename="document"')
+          .end(done)
       })
 
-      it('should be ignored case-insensitively', function (done) {
-        var app = express()
+      it('should be ignored case-insensitively', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.download('test/fixtures/user.html', 'document', {
             headers: {
               'content-type': 'text/x-custom',
@@ -443,40 +443,40 @@ describe('res', function(){
         })
 
         request(app)
-        .get('/')
-        .expect(200)
-        .expect('Content-Type', 'text/x-custom')
-        .expect('Content-Disposition', 'attachment; filename="document"')
-        .end(done)
+          .get('/')
+          .expect(200)
+          .expect('Content-Type', 'text/x-custom')
+          .expect('Content-Disposition', 'attachment; filename="document"')
+          .end(done)
       })
     })
   })
 
-  describe('on failure', function(){
-    it('should invoke the callback', function(done){
-      var app = express();
+  describe('on failure', () => {
+    it('should invoke the callback', (done) => {
+      const app = express()
 
-      app.use(function (req, res, next) {
-        res.download('test/fixtures/foobar.html', function(err){
-          if (!err) return next(new Error('expected error'));
-          res.send('got ' + err.status + ' ' + err.code);
-        });
-      });
+      app.use((req, res, next) => {
+        res.download('test/fixtures/foobar.html', (err) => {
+          if (!err) return next(new Error('expected error'))
+          res.send('got ' + err.status + ' ' + err.code)
+        })
+      })
 
       request(app)
-      .get('/')
-      .expect(200, 'got 404 ENOENT', done);
+        .get('/')
+        .expect(200, 'got 404 ENOENT', done)
     })
 
-    it('should remove Content-Disposition', function(done){
-      var app = express()
+    it('should remove Content-Disposition', (done) => {
+      const app = express()
 
-      app.use(function (req, res, next) {
-        res.download('test/fixtures/foobar.html', function(err){
-          if (!err) return next(new Error('expected error'));
-          res.end('failed');
-        });
-      });
+      app.use((req, res, next) => {
+        res.download('test/fixtures/foobar.html', (err) => {
+          if (!err) return next(new Error('expected error'))
+          res.end('failed')
+        })
+      })
 
       request(app)
         .get('/')
diff --git a/test/res.format.js b/test/res.format.js
index 0d770d57651..e46e48865b9 100644
--- a/test/res.format.js
+++ b/test/res.format.js
@@ -1,57 +1,57 @@
 'use strict'
 
-var after = require('after')
-var express = require('../')
-  , request = require('supertest')
-  , assert = require('node:assert');
+const after = require('after')
+const express = require('../')
+const request = require('supertest')
+const assert = require('node:assert')
 
-var app1 = express();
+const app1 = express()
 
-app1.use(function(req, res, next){
+app1.use((req, res, next) => {
   res.format({
-    'text/plain': function(){
-      res.send('hey');
+    'text/plain': function () {
+      res.send('hey')
     },
 
-    'text/html': function(){
-      res.send('<p>hey</p>');
+    'text/html': function () {
+      res.send('<p>hey</p>')
     },
 
-    'application/json': function(a, b, c){
+    'application/json': function (a, b, c) {
       assert(req === a)
       assert(res === b)
       assert(next === c)
-      res.send({ message: 'hey' });
+      res.send({ message: 'hey' })
     }
-  });
-});
+  })
+})
 
-app1.use(function(err, req, res, next){
-  if (!err.types) throw err;
+app1.use((err, req, res, next) => {
+  if (!err.types) throw err
   res.status(err.status)
   res.send('Supports: ' + err.types.join(', '))
 })
 
-var app2 = express();
+const app2 = express()
 
-app2.use(function(req, res, next){
+app2.use((req, res, next) => {
   res.format({
-    text: function(){ res.send('hey') },
-    html: function(){ res.send('<p>hey</p>') },
-    json: function(){ res.send({ message: 'hey' }) }
-  });
-});
+    text: function () { res.send('hey') },
+    html: function () { res.send('<p>hey</p>') },
+    json: function () { res.send({ message: 'hey' }) }
+  })
+})
 
-app2.use(function(err, req, res, next){
+app2.use((err, req, res, next) => {
   res.status(err.status)
   res.send('Supports: ' + err.types.join(', '))
 })
 
-var app3 = express();
+const app3 = express()
 
-app3.use(function(req, res, next){
+app3.use((req, res, next) => {
   res.format({
-    text: function(){ res.send('hey') },
+    text: function () { res.send('hey') },
     default: function (a, b, c) {
       assert(req === a)
       assert(res === b)
@@ -59,79 +59,79 @@ app3.use(function(req, res, next){
       res.send('default')
     }
   })
-});
+})
 
-var app4 = express();
+const app4 = express()
 
-app4.get('/', function (req, res) {
+app4.get('/', (req, res) => {
   res.format({
-    text: function(){ res.send('hey') },
-    html: function(){ res.send('<p>hey</p>') },
-    json: function(){ res.send({ message: 'hey' }) }
-  });
-});
+    text: function () { res.send('hey') },
+    html: function () { res.send('<p>hey</p>') },
+    json: function () { res.send({ message: 'hey' }) }
+  })
+})
 
-app4.use(function(err, req, res, next){
+app4.use((err, req, res, next) => {
   res.status(err.status)
   res.send('Supports: ' + err.types.join(', '))
 })
 
-var app5 = express();
+const app5 = express()
 
-app5.use(function (req, res, next) {
+app5.use((req, res, next) => {
   res.format({
     default: function () { res.send('hey') }
-  });
-});
+  })
+})
 
-describe('res', function(){
-  describe('.format(obj)', function(){
-    describe('with canonicalized mime types', function(){
-      test(app1);
+describe('res', () => {
+  describe('.format(obj)', () => {
+    describe('with canonicalized mime types', () => {
+      test(app1)
     })
 
-    describe('with extnames', function(){
-      test(app2);
+    describe('with extnames', () => {
+      test(app2)
     })
 
-    describe('with parameters', function(){
-      var app = express();
+    describe('with parameters', () => {
+      const app = express()
 
-      app.use(function(req, res, next){
+      app.use((req, res, next) => {
         res.format({
-          'text/plain; charset=utf-8': function(){ res.send('hey') },
-          'text/html; foo=bar; bar=baz': function(){ res.send('<p>hey</p>') },
-          'application/json; q=0.5': function(){ res.send({ message: 'hey' }) }
-        });
-      });
+          'text/plain; charset=utf-8': function () { res.send('hey') },
+          'text/html; foo=bar; bar=baz': function () { res.send('<p>hey</p>') },
+          'application/json; q=0.5': function () { res.send({ message: 'hey' }) }
+        })
+      })
 
-      app.use(function(err, req, res, next){
+      app.use((err, req, res, next) => {
         res.status(err.status)
         res.send('Supports: ' + err.types.join(', '))
-      });
+      })
 
-      test(app);
+      test(app)
     })
 
-    describe('given .default', function(){
-      it('should be invoked instead of auto-responding', function(done){
+    describe('given .default', () => {
+      it('should be invoked instead of auto-responding', (done) => {
         request(app3)
-        .get('/')
-        .set('Accept', 'text/html')
-        .expect('default', done);
+          .get('/')
+          .set('Accept', 'text/html')
+          .expect('default', done)
       })
 
-      it('should work when only .default is provided', function (done) {
+      it('should work when only .default is provided', (done) => {
         request(app5)
-        .get('/')
-        .set('Accept', '*/*')
-        .expect('hey', done);
+          .get('/')
+          .set('Accept', '*/*')
+          .expect('hey', done)
       })
 
-      it('should be able to invoke other formatter', function (done) {
-        var app = express()
+      it('should be able to invoke other formatter', (done) => {
+        const app = express()
 
-        app.use(function (req, res, next) {
+        app.use((req, res, next) => {
           res.format({
             json: function () { res.send('json') },
             default: function () {
@@ -151,23 +151,23 @@ describe('res', function(){
       })
     })
 
-    describe('in router', function(){
-      test(app4);
+    describe('in router', () => {
+      test(app4)
     })
 
-    describe('in router', function(){
-      var app = express();
-      var router = express.Router();
+    describe('in router', () => {
+      const app = express()
+      const router = express.Router()
 
-      router.get('/', function (req, res) {
+      router.get('/', (req, res) => {
         res.format({
-          text: function(){ res.send('hey') },
-          html: function(){ res.send('<p>hey</p>') },
-          json: function(){ res.send({ message: 'hey' }) }
-        });
-      });
+          text: function () { res.send('hey') },
+          html: function () { res.send('<p>hey</p>') },
+          json: function () { res.send({ message: 'hey' }) }
+        })
+      })
 
-      router.use(function(err, req, res, next){
+      router.use((err, req, res, next) => {
         res.status(err.status)
         res.send('Supports: ' + err.types.join(', '))
       })
@@ -179,70 +179,70 @@ describe('res', function(){
   })
 })
 
-function test(app) {
-  it('should utilize qvalues in negotiation', function(done){
+function test (app) {
+  it('should utilize qvalues in negotiation', (done) => {
     request(app)
-    .get('/')
-    .set('Accept', 'text/html; q=.5, application/json, */*; q=.1')
-    .expect({"message":"hey"}, done);
+      .get('/')
+      .set('Accept', 'text/html; q=.5, application/json, */*; q=.1')
+      .expect({ message: 'hey' }, done)
   })
 
-  it('should allow wildcard type/subtypes', function(done){
+  it('should allow wildcard type/subtypes', (done) => {
     request(app)
-    .get('/')
-    .set('Accept', 'text/html; q=.5, application/*, */*; q=.1')
-    .expect({"message":"hey"}, done);
+      .get('/')
+      .set('Accept', 'text/html; q=.5, application/*, */*; q=.1')
+      .expect({ message: 'hey' }, done)
   })
 
-  it('should default the Content-Type', function(done){
+  it('should default the Content-Type', (done) => {
     request(app)
-    .get('/')
-    .set('Accept', 'text/html; q=.5, text/plain')
-    .expect('Content-Type', 'text/plain; charset=utf-8')
-    .expect('hey', done);
+      .get('/')
+      .set('Accept', 'text/html; q=.5, text/plain')
+      .expect('Content-Type', 'text/plain; charset=utf-8')
+      .expect('hey', done)
   })
 
-  it('should set the correct charset for the Content-Type', function (done) {
-    var cb = after(3, done)
+  it('should set the correct charset for the Content-Type', (done) => {
+    const cb = after(3, done)
 
     request(app)
-    .get('/')
-    .set('Accept', 'text/html')
-    .expect('Content-Type', 'text/html; charset=utf-8', cb)
+      .get('/')
+      .set('Accept', 'text/html')
+      .expect('Content-Type', 'text/html; charset=utf-8', cb)
 
     request(app)
-    .get('/')
-    .set('Accept', 'text/plain')
-    .expect('Content-Type', 'text/plain; charset=utf-8', cb)
+      .get('/')
+      .set('Accept', 'text/plain')
+      .expect('Content-Type', 'text/plain; charset=utf-8', cb)
 
     request(app)
-    .get('/')
-    .set('Accept', 'application/json')
-    .expect('Content-Type', 'application/json; charset=utf-8', cb)
+      .get('/')
+      .set('Accept', 'application/json')
+      .expect('Content-Type', 'application/json; charset=utf-8', cb)
   })
 
-  it('should Vary: Accept', function(done){
+  it('should Vary: Accept', (done) => {
     request(app)
-    .get('/')
-    .set('Accept', 'text/html; q=.5, text/plain')
-    .expect('Vary', 'Accept', done);
+      .get('/')
+      .set('Accept', 'text/html; q=.5, text/plain')
+      .expect('Vary', 'Accept', done)
   })
 
-  describe('when Accept is not present', function(){
-    it('should invoke the first callback', function(done){
+  describe('when Accept is not present', () => {
+    it('should invoke the first callback', (done) => {
       request(app)
-      .get('/')
-      .expect('hey', done);
+        .get('/')
+        .expect('hey', done)
     })
   })
 
-  describe('when no match is made', function(){
-    it('should respond with 406 not acceptable', function(done){
+  describe('when no match is made', () => {
+    it('should respond with 406 not acceptable', (done) => {
       request(app)
-      .get('/')
-      .set('Accept', 'foo/bar')
-      .expect('Supports: text/plain, text/html, application/json')
-      .expect(406, done)
+        .get('/')
+        .set('Accept', 'foo/bar')
+        .expect('Supports: text/plain, text/html, application/json')
+        .expect(406, done)
     })
   })
 }
diff --git a/test/res.get.js b/test/res.get.js
index a5f12e2e539..9c4fba98222 100644
--- a/test/res.get.js
+++ b/test/res.get.js
@@ -1,21 +1,21 @@
 'use strict'
 
-var express = require('..');
-var request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function(){
-  describe('.get(field)', function(){
-    it('should get the response header field', function (done) {
-      var app = express();
+describe('res', () => {
+  describe('.get(field)', () => {
+    it('should get the response header field', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.setHeader('Content-Type', 'text/x-foo');
-        res.send(res.get('Content-Type'));
-      });
+      app.use((req, res) => {
+        res.setHeader('Content-Type', 'text/x-foo')
+        res.send(res.get('Content-Type'))
+      })
 
       request(app)
-      .get('/')
-      .expect(200, 'text/x-foo', done);
+        .get('/')
+        .expect(200, 'text/x-foo', done)
     })
   })
 })
diff --git a/test/res.json.js b/test/res.json.js
index ffd547e95b2..0a9f5517bae 100644
--- a/test/res.json.js
+++ b/test/res.json.js
@@ -1,135 +1,135 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest')
-  , assert = require('node:assert');
+const express = require('../')
+const request = require('supertest')
+const assert = require('node:assert')
 
-describe('res', function(){
-  describe('.json(object)', function(){
-    it('should not support jsonp callbacks', function(done){
-      var app = express();
+describe('res', () => {
+  describe('.json(object)', () => {
+    it('should not support jsonp callbacks', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.json({ foo: 'bar' });
-      });
+      app.use((req, res) => {
+        res.json({ foo: 'bar' })
+      })
 
       request(app)
-      .get('/?callback=foo')
-      .expect('{"foo":"bar"}', done);
+        .get('/?callback=foo')
+        .expect('{"foo":"bar"}', done)
     })
 
-    it('should not override previous Content-Types', function(done){
-      var app = express();
+    it('should not override previous Content-Types', (done) => {
+      const app = express()
 
-      app.get('/', function(req, res){
-        res.type('application/vnd.example+json');
-        res.json({ hello: 'world' });
-      });
+      app.get('/', (req, res) => {
+        res.type('application/vnd.example+json')
+        res.json({ hello: 'world' })
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'application/vnd.example+json; charset=utf-8')
-      .expect(200, '{"hello":"world"}', done);
+        .get('/')
+        .expect('Content-Type', 'application/vnd.example+json; charset=utf-8')
+        .expect(200, '{"hello":"world"}', done)
     })
 
-    describe('when given primitives', function(){
-      it('should respond with json for null', function(done){
-        var app = express();
+    describe('when given primitives', () => {
+      it('should respond with json for null', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.json(null);
-        });
+        app.use((req, res) => {
+          res.json(null)
+        })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, 'null', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, 'null', done)
       })
 
-      it('should respond with json for Number', function(done){
-        var app = express();
+      it('should respond with json for Number', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.json(300);
-        });
+        app.use((req, res) => {
+          res.json(300)
+        })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '300', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '300', done)
       })
 
-      it('should respond with json for String', function(done){
-        var app = express();
+      it('should respond with json for String', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.json('str');
-        });
+        app.use((req, res) => {
+          res.json('str')
+        })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '"str"', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '"str"', done)
       })
     })
 
-    describe('when given an array', function(){
-      it('should respond with json', function(done){
-        var app = express();
+    describe('when given an array', () => {
+      it('should respond with json', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.json(['foo', 'bar', 'baz']);
-        });
+        app.use((req, res) => {
+          res.json(['foo', 'bar', 'baz'])
+        })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '["foo","bar","baz"]', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '["foo","bar","baz"]', done)
       })
     })
 
-    describe('when given an object', function(){
-      it('should respond with json', function(done){
-        var app = express();
+    describe('when given an object', () => {
+      it('should respond with json', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.json({ name: 'tobi' });
-        });
+        app.use((req, res) => {
+          res.json({ name: 'tobi' })
+        })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '{"name":"tobi"}', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '{"name":"tobi"}', done)
       })
     })
 
-    describe('"json escape" setting', function () {
-      it('should be undefined by default', function () {
-        var app = express()
+    describe('"json escape" setting', () => {
+      it('should be undefined by default', () => {
+        const app = express()
         assert.strictEqual(app.get('json escape'), undefined)
       })
 
-      it('should unicode escape HTML-sniffing characters', function (done) {
-        var app = express()
+      it('should unicode escape HTML-sniffing characters', (done) => {
+        const app = express()
 
         app.enable('json escape')
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.json({ '&': '<script>' })
         })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '{"\\u0026":"\\u003cscript\\u003e"}', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '{"\\u0026":"\\u003cscript\\u003e"}', done)
       })
 
-      it('should not break undefined escape', function (done) {
-        var app = express()
+      it('should not break undefined escape', (done) => {
+        const app = express()
 
         app.enable('json escape')
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.json(undefined)
         })
 
@@ -140,46 +140,44 @@ describe('res', function(){
       })
     })
 
-    describe('"json replacer" setting', function(){
-      it('should be passed to JSON.stringify()', function(done){
-        var app = express();
+    describe('"json replacer" setting', () => {
+      it('should be passed to JSON.stringify()', (done) => {
+        const app = express()
 
-        app.set('json replacer', function(key, val){
-          return key[0] === '_'
-            ? undefined
-            : val;
-        });
+        app.set('json replacer', (key, val) => key[0] === '_'
+          ? undefined
+          : val)
 
-        app.use(function(req, res){
-          res.json({ name: 'tobi', _id: 12345 });
-        });
+        app.use((req, res) => {
+          res.json({ name: 'tobi', _id: 12345 })
+        })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '{"name":"tobi"}', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '{"name":"tobi"}', done)
       })
     })
 
-    describe('"json spaces" setting', function(){
-      it('should be undefined by default', function(){
-        var app = express();
-        assert(undefined === app.get('json spaces'));
+    describe('"json spaces" setting', () => {
+      it('should be undefined by default', () => {
+        const app = express()
+        assert(undefined === app.get('json spaces'))
       })
 
-      it('should be passed to JSON.stringify()', function(done){
-        var app = express();
+      it('should be passed to JSON.stringify()', (done) => {
+        const app = express()
 
-        app.set('json spaces', 2);
+        app.set('json spaces', 2)
 
-        app.use(function(req, res){
-          res.json({ name: 'tobi', age: 2 });
-        });
+        app.use((req, res) => {
+          res.json({ name: 'tobi', age: 2 })
+        })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '{\n  "name": "tobi",\n  "age": 2\n}', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '{\n  "name": "tobi",\n  "age": 2\n}', done)
       })
     })
   })
diff --git a/test/res.jsonp.js b/test/res.jsonp.js
index c1f90f11092..c563780c5c3 100644
--- a/test/res.jsonp.js
+++ b/test/res.jsonp.js
@@ -1,167 +1,167 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest')
-  , assert = require('node:assert');
-var utils = require('./support/utils');
-
-describe('res', function(){
-  describe('.jsonp(object)', function(){
-    it('should respond with jsonp', function(done){
-      var app = express();
-
-      app.use(function(req, res){
-        res.jsonp({ count: 1 });
-      });
+const express = require('../')
+const request = require('supertest')
+const assert = require('node:assert')
+const utils = require('./support/utils')
+
+describe('res', () => {
+  describe('.jsonp(object)', () => {
+    it('should respond with jsonp', (done) => {
+      const app = express()
+
+      app.use((req, res) => {
+        res.jsonp({ count: 1 })
+      })
 
       request(app)
-      .get('/?callback=something')
-      .expect('Content-Type', 'text/javascript; charset=utf-8')
-      .expect(200, /something\(\{"count":1\}\);/, done);
+        .get('/?callback=something')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .expect(200, /something\(\{"count":1\}\);/, done)
     })
 
-    it('should use first callback parameter with jsonp', function(done){
-      var app = express();
+    it('should use first callback parameter with jsonp', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.jsonp({ count: 1 });
-      });
+      app.use((req, res) => {
+        res.jsonp({ count: 1 })
+      })
 
       request(app)
-      .get('/?callback=something&callback=somethingelse')
-      .expect('Content-Type', 'text/javascript; charset=utf-8')
-      .expect(200, /something\(\{"count":1\}\);/, done);
+        .get('/?callback=something&callback=somethingelse')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .expect(200, /something\(\{"count":1\}\);/, done)
     })
 
-    it('should ignore object callback parameter with jsonp', function(done){
-      var app = express();
+    it('should ignore object callback parameter with jsonp', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.jsonp({ count: 1 });
-      });
+      app.use((req, res) => {
+        res.jsonp({ count: 1 })
+      })
 
       request(app)
-      .get('/?callback[a]=something')
-      .expect('Content-Type', 'application/json; charset=utf-8')
-      .expect(200, '{"count":1}', done)
+        .get('/?callback[a]=something')
+        .expect('Content-Type', 'application/json; charset=utf-8')
+        .expect(200, '{"count":1}', done)
     })
 
-    it('should allow renaming callback', function(done){
-      var app = express();
+    it('should allow renaming callback', (done) => {
+      const app = express()
 
-      app.set('jsonp callback name', 'clb');
+      app.set('jsonp callback name', 'clb')
 
-      app.use(function(req, res){
-        res.jsonp({ count: 1 });
-      });
+      app.use((req, res) => {
+        res.jsonp({ count: 1 })
+      })
 
       request(app)
-      .get('/?clb=something')
-      .expect('Content-Type', 'text/javascript; charset=utf-8')
-      .expect(200, /something\(\{"count":1\}\);/, done);
+        .get('/?clb=something')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .expect(200, /something\(\{"count":1\}\);/, done)
     })
 
-    it('should allow []', function(done){
-      var app = express();
+    it('should allow []', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.jsonp({ count: 1 });
-      });
+      app.use((req, res) => {
+        res.jsonp({ count: 1 })
+      })
 
       request(app)
-      .get('/?callback=callbacks[123]')
-      .expect('Content-Type', 'text/javascript; charset=utf-8')
-      .expect(200, /callbacks\[123\]\(\{"count":1\}\);/, done);
+        .get('/?callback=callbacks[123]')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .expect(200, /callbacks\[123\]\(\{"count":1\}\);/, done)
     })
 
-    it('should disallow arbitrary js', function(done){
-      var app = express();
+    it('should disallow arbitrary js', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.jsonp({});
-      });
+      app.use((req, res) => {
+        res.jsonp({})
+      })
 
       request(app)
-      .get('/?callback=foo;bar()')
-      .expect('Content-Type', 'text/javascript; charset=utf-8')
-      .expect(200, /foobar\(\{\}\);/, done);
+        .get('/?callback=foo;bar()')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .expect(200, /foobar\(\{\}\);/, done)
     })
 
-    it('should escape utf whitespace', function(done){
-      var app = express();
+    it('should escape utf whitespace', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.jsonp({ str: '\u2028 \u2029 woot' });
-      });
+      app.use((req, res) => {
+        res.jsonp({ str: '\u2028 \u2029 woot' })
+      })
 
       request(app)
-      .get('/?callback=foo')
-      .expect('Content-Type', 'text/javascript; charset=utf-8')
-      .expect(200, /foo\(\{"str":"\\u2028 \\u2029 woot"\}\);/, done);
-    });
+        .get('/?callback=foo')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .expect(200, /foo\(\{"str":"\\u2028 \\u2029 woot"\}\);/, done)
+    })
 
-    it('should not escape utf whitespace for json fallback', function(done){
-      var app = express();
+    it('should not escape utf whitespace for json fallback', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.jsonp({ str: '\u2028 \u2029 woot' });
-      });
+      app.use((req, res) => {
+        res.jsonp({ str: '\u2028 \u2029 woot' })
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'application/json; charset=utf-8')
-      .expect(200, '{"str":"\u2028 \u2029 woot"}', done);
-    });
+        .get('/')
+        .expect('Content-Type', 'application/json; charset=utf-8')
+        .expect(200, '{"str":"\u2028 \u2029 woot"}', done)
+    })
 
-    it('should include security header and prologue', function (done) {
-      var app = express();
+    it('should include security header and prologue', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.jsonp({ count: 1 });
-      });
+      app.use((req, res) => {
+        res.jsonp({ count: 1 })
+      })
 
       request(app)
-      .get('/?callback=something')
-      .expect('Content-Type', 'text/javascript; charset=utf-8')
-      .expect('X-Content-Type-Options', 'nosniff')
-      .expect(200, /^\/\*\*\//, done);
+        .get('/?callback=something')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .expect('X-Content-Type-Options', 'nosniff')
+        .expect(200, /^\/\*\*\//, done)
     })
 
-    it('should not override previous Content-Types with no callback', function(done){
-      var app = express();
+    it('should not override previous Content-Types with no callback', (done) => {
+      const app = express()
 
-      app.get('/', function(req, res){
-        res.type('application/vnd.example+json');
-        res.jsonp({ hello: 'world' });
-      });
+      app.get('/', (req, res) => {
+        res.type('application/vnd.example+json')
+        res.jsonp({ hello: 'world' })
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'application/vnd.example+json; charset=utf-8')
-      .expect(utils.shouldNotHaveHeader('X-Content-Type-Options'))
-      .expect(200, '{"hello":"world"}', done);
+        .get('/')
+        .expect('Content-Type', 'application/vnd.example+json; charset=utf-8')
+        .expect(utils.shouldNotHaveHeader('X-Content-Type-Options'))
+        .expect(200, '{"hello":"world"}', done)
     })
 
-    it('should override previous Content-Types with callback', function(done){
-      var app = express();
+    it('should override previous Content-Types with callback', (done) => {
+      const app = express()
 
-      app.get('/', function(req, res){
-        res.type('application/vnd.example+json');
-        res.jsonp({ hello: 'world' });
-      });
+      app.get('/', (req, res) => {
+        res.type('application/vnd.example+json')
+        res.jsonp({ hello: 'world' })
+      })
 
       request(app)
-      .get('/?callback=cb')
-      .expect('Content-Type', 'text/javascript; charset=utf-8')
-      .expect('X-Content-Type-Options', 'nosniff')
-      .expect(200, /cb\(\{"hello":"world"\}\);$/, done);
+        .get('/?callback=cb')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .expect('X-Content-Type-Options', 'nosniff')
+        .expect(200, /cb\(\{"hello":"world"\}\);$/, done)
     })
 
-    describe('when given undefined', function () {
-      it('should invoke callback with no arguments', function (done) {
-        var app = express()
+    describe('when given undefined', () => {
+      it('should invoke callback with no arguments', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.jsonp(undefined)
         })
 
@@ -172,11 +172,11 @@ describe('res', function(){
       })
     })
 
-    describe('when given null', function () {
-      it('should invoke callback with null', function (done) {
-        var app = express()
+    describe('when given null', () => {
+      it('should invoke callback with null', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.jsonp(null)
         })
 
@@ -187,11 +187,11 @@ describe('res', function(){
       })
     })
 
-    describe('when given a string', function () {
-      it('should invoke callback with a string', function (done) {
-        var app = express()
+    describe('when given a string', () => {
+      it('should invoke callback with a string', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.jsonp('tobi')
         })
 
@@ -202,11 +202,11 @@ describe('res', function(){
       })
     })
 
-    describe('when given a number', function () {
-      it('should invoke callback with a number', function (done) {
-        var app = express()
+    describe('when given a number', () => {
+      it('should invoke callback with a number', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.jsonp(42)
         })
 
@@ -217,11 +217,11 @@ describe('res', function(){
       })
     })
 
-    describe('when given an array', function () {
-      it('should invoke callback with an array', function (done) {
-        var app = express()
+    describe('when given an array', () => {
+      it('should invoke callback with an array', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.jsonp(['foo', 'bar', 'baz'])
         })
 
@@ -232,11 +232,11 @@ describe('res', function(){
       })
     })
 
-    describe('when given an object', function () {
-      it('should invoke callback with an object', function (done) {
-        var app = express()
+    describe('when given an object', () => {
+      it('should invoke callback with an object', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.jsonp({ name: 'tobi' })
         })
 
@@ -247,33 +247,33 @@ describe('res', function(){
       })
     })
 
-    describe('"json escape" setting', function () {
-      it('should be undefined by default', function () {
-        var app = express()
+    describe('"json escape" setting', () => {
+      it('should be undefined by default', () => {
+        const app = express()
         assert.strictEqual(app.get('json escape'), undefined)
       })
 
-      it('should unicode escape HTML-sniffing characters', function (done) {
-        var app = express()
+      it('should unicode escape HTML-sniffing characters', (done) => {
+        const app = express()
 
         app.enable('json escape')
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.jsonp({ '&': '\u2028<script>\u2029' })
         })
 
         request(app)
-        .get('/?callback=foo')
-        .expect('Content-Type', 'text/javascript; charset=utf-8')
-        .expect(200, /foo\({"\\u0026":"\\u2028\\u003cscript\\u003e\\u2029"}\)/, done)
+          .get('/?callback=foo')
+          .expect('Content-Type', 'text/javascript; charset=utf-8')
+          .expect(200, /foo\({"\\u0026":"\\u2028\\u003cscript\\u003e\\u2029"}\)/, done)
       })
 
-      it('should not break undefined escape', function (done) {
-        var app = express()
+      it('should not break undefined escape', (done) => {
+        const app = express()
 
         app.enable('json escape')
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.jsonp(undefined)
         })
 
@@ -284,61 +284,59 @@ describe('res', function(){
       })
     })
 
-    describe('"json replacer" setting', function(){
-      it('should be passed to JSON.stringify()', function(done){
-        var app = express();
+    describe('"json replacer" setting', () => {
+      it('should be passed to JSON.stringify()', (done) => {
+        const app = express()
 
-        app.set('json replacer', function(key, val){
-          return key[0] === '_'
-            ? undefined
-            : val;
-        });
+        app.set('json replacer', (key, val) => key[0] === '_'
+          ? undefined
+          : val)
 
-        app.use(function(req, res){
-          res.jsonp({ name: 'tobi', _id: 12345 });
-        });
+        app.use((req, res) => {
+          res.jsonp({ name: 'tobi', _id: 12345 })
+        })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '{"name":"tobi"}', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '{"name":"tobi"}', done)
       })
     })
 
-    describe('"json spaces" setting', function(){
-      it('should be undefined by default', function(){
-        var app = express();
-        assert(undefined === app.get('json spaces'));
+    describe('"json spaces" setting', () => {
+      it('should be undefined by default', () => {
+        const app = express()
+        assert(undefined === app.get('json spaces'))
       })
 
-      it('should be passed to JSON.stringify()', function(done){
-        var app = express();
+      it('should be passed to JSON.stringify()', (done) => {
+        const app = express()
 
-        app.set('json spaces', 2);
+        app.set('json spaces', 2)
 
-        app.use(function(req, res){
-          res.jsonp({ name: 'tobi', age: 2 });
-        });
+        app.use((req, res) => {
+          res.jsonp({ name: 'tobi', age: 2 })
+        })
 
         request(app)
-        .get('/')
-        .expect('Content-Type', 'application/json; charset=utf-8')
-        .expect(200, '{\n  "name": "tobi",\n  "age": 2\n}', done)
+          .get('/')
+          .expect('Content-Type', 'application/json; charset=utf-8')
+          .expect(200, '{\n  "name": "tobi",\n  "age": 2\n}', done)
       })
     })
   })
 
-  it('should not override previous Content-Types', function(done){
-    var app = express();
+  it('should not override previous Content-Types', (done) => {
+    const app = express()
 
-    app.get('/', function(req, res){
-      res.type('application/vnd.example+json');
-      res.jsonp({ hello: 'world' });
-    });
+    app.get('/', (req, res) => {
+      res.type('application/vnd.example+json')
+      res.jsonp({ hello: 'world' })
+    })
 
     request(app)
-    .get('/')
-    .expect('content-type', 'application/vnd.example+json; charset=utf-8')
-    .expect(200, '{"hello":"world"}', done)
+      .get('/')
+      .expect('content-type', 'application/vnd.example+json; charset=utf-8')
+      .expect(200, '{"hello":"world"}', done)
   })
 })
diff --git a/test/res.links.js b/test/res.links.js
index 40665fd558a..d48546a767a 100644
--- a/test/res.links.js
+++ b/test/res.links.js
@@ -1,65 +1,65 @@
 'use strict'
 
-var express = require('..');
-var request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function(){
-  describe('.links(obj)', function(){
-    it('should set Link header field', function (done) {
-      var app = express();
+describe('res', () => {
+  describe('.links(obj)', () => {
+    it('should set Link header field', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.links({
           next: 'http://api.example.com/users?page=2',
           last: 'http://api.example.com/users?page=5'
-        });
-        res.end();
-      });
+        })
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Link', '<http://api.example.com/users?page=2>; rel="next", <http://api.example.com/users?page=5>; rel="last"')
-      .expect(200, done);
+        .get('/')
+        .expect('Link', '<http://api.example.com/users?page=2>; rel="next", <http://api.example.com/users?page=5>; rel="last"')
+        .expect(200, done)
     })
 
-    it('should set Link header field for multiple calls', function (done) {
-      var app = express();
+    it('should set Link header field for multiple calls', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.links({
           next: 'http://api.example.com/users?page=2',
           last: 'http://api.example.com/users?page=5'
-        });
+        })
 
         res.links({
           prev: 'http://api.example.com/users?page=1'
-        });
+        })
 
-        res.end();
-      });
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Link', '<http://api.example.com/users?page=2>; rel="next", <http://api.example.com/users?page=5>; rel="last", <http://api.example.com/users?page=1>; rel="prev"')
-      .expect(200, done);
+        .get('/')
+        .expect('Link', '<http://api.example.com/users?page=2>; rel="next", <http://api.example.com/users?page=5>; rel="last", <http://api.example.com/users?page=1>; rel="prev"')
+        .expect(200, done)
     })
 
-    it('should set multiple links for single rel', function (done) {
-      var app = express();
+    it('should set multiple links for single rel', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.links({
           next: 'http://api.example.com/users?page=2',
           last: ['http://api.example.com/users?page=5', 'http://api.example.com/users?page=1']
-        });
+        })
 
-        res.end();
-      });
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Link', '<http://api.example.com/users?page=2>; rel="next", <http://api.example.com/users?page=5>; rel="last", <http://api.example.com/users?page=1>; rel="last"')
-      .expect(200, done);
+        .get('/')
+        .expect('Link', '<http://api.example.com/users?page=2>; rel="next", <http://api.example.com/users?page=5>; rel="last", <http://api.example.com/users?page=1>; rel="last"')
+        .expect(200, done)
     })
   })
 })
diff --git a/test/res.locals.js b/test/res.locals.js
index c4365b36f35..cbf706dc2af 100644
--- a/test/res.locals.js
+++ b/test/res.locals.js
@@ -1,40 +1,40 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function(){
-  describe('.locals', function(){
-    it('should be empty by default', function(done){
-      var app = express();
+describe('res', () => {
+  describe('.locals', () => {
+    it('should be empty by default', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.json(res.locals)
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect(200, {}, done)
+        .get('/')
+        .expect(200, {}, done)
     })
   })
 
-  it('should work when mounted', function(done){
-    var app = express();
-    var blog = express();
+  it('should work when mounted', (done) => {
+    const app = express()
+    const blog = express()
 
-    app.use(blog);
+    app.use(blog)
 
-    blog.use(function(req, res, next){
-      res.locals.foo = 'bar';
-      next();
-    });
+    blog.use((req, res, next) => {
+      res.locals.foo = 'bar'
+      next()
+    })
 
-    app.use(function(req, res){
+    app.use((req, res) => {
       res.json(res.locals)
-    });
+    })
 
     request(app)
-    .get('/')
-    .expect(200, { foo: 'bar' }, done)
+      .get('/')
+      .expect(200, { foo: 'bar' }, done)
   })
 })
diff --git a/test/res.location.js b/test/res.location.js
index b81c6f07d8d..28f2114e390 100644
--- a/test/res.location.js
+++ b/test/res.location.js
@@ -1,56 +1,56 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest')
-  , assert = require('node:assert')
-  , url = require('node:url');
-
-describe('res', function(){
-  describe('.location(url)', function(){
-    it('should set the header', function(done){
-      var app = express();
-
-      app.use(function(req, res){
-        res.location('http://google.com/').end();
-      });
+const express = require('../')
+const request = require('supertest')
+const assert = require('node:assert')
+const url = require('node:url')
+
+describe('res', () => {
+  describe('.location(url)', () => {
+    it('should set the header', (done) => {
+      const app = express()
+
+      app.use((req, res) => {
+        res.location('http://google.com/').end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Location', 'http://google.com/')
-      .expect(200, done)
+        .get('/')
+        .expect('Location', 'http://google.com/')
+        .expect(200, done)
     })
 
-    it('should preserve trailing slashes when not present', function(done){
-      var app = express();
+    it('should preserve trailing slashes when not present', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.location('http://google.com').end();
-      });
+      app.use((req, res) => {
+        res.location('http://google.com').end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Location', 'http://google.com')
-      .expect(200, done)
+        .get('/')
+        .expect('Location', 'http://google.com')
+        .expect(200, done)
     })
 
-    it('should encode "url"', function (done) {
-      var app = express()
+    it('should encode "url"', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.location('https://google.com?q=\u2603 §10').end()
       })
 
       request(app)
-      .get('/')
-      .expect('Location', 'https://google.com?q=%E2%98%83%20%C2%A710')
-      .expect(200, done)
+        .get('/')
+        .expect('Location', 'https://google.com?q=%E2%98%83%20%C2%A710')
+        .expect(200, done)
     })
 
-    it('should encode data uri1', function (done) {
-      var app = express()
-      app.use(function (req, res) {
-        res.location('data:text/javascript,export default () => { }').end();
-      });
+    it('should encode data uri1', (done) => {
+      const app = express()
+      app.use((req, res) => {
+        res.location('data:text/javascript,export default () => { }').end()
+      })
 
       request(app)
         .get('/')
@@ -58,11 +58,11 @@ describe('res', function(){
         .expect(200, done)
     })
 
-    it('should encode data uri2', function (done) {
-      var app = express()
-      app.use(function (req, res) {
-        res.location('data:text/javascript,export default () => { }').end();
-      });
+    it('should encode data uri2', (done) => {
+      const app = express()
+      app.use((req, res) => {
+        res.location('data:text/javascript,export default () => { }').end()
+      })
 
       request(app)
         .get('/')
@@ -70,84 +70,84 @@ describe('res', function(){
         .expect(200, done)
     })
 
-    it('should consistently handle non-string input: boolean', function (done) {
-      var app = express()
-      app.use(function (req, res) {
-        res.location(true).end();
-      });
+    it('should consistently handle non-string input: boolean', (done) => {
+      const app = express()
+      app.use((req, res) => {
+        res.location(true).end()
+      })
 
       request(app)
         .get('/')
         .expect('Location', 'true')
         .expect(200, done)
-    });
+    })
 
-    it('should consistently handle non-string inputs: object', function (done) {
-      var app = express()
-      app.use(function (req, res) {
-        res.location({}).end();
-      });
+    it('should consistently handle non-string inputs: object', (done) => {
+      const app = express()
+      app.use((req, res) => {
+        res.location({}).end()
+      })
 
       request(app)
         .get('/')
         .expect('Location', '[object%20Object]')
         .expect(200, done)
-    });
+    })
 
-    it('should consistently handle non-string inputs: array', function (done) {
-      var app = express()
-      app.use(function (req, res) {
-        res.location([]).end();
-      });
+    it('should consistently handle non-string inputs: array', (done) => {
+      const app = express()
+      app.use((req, res) => {
+        res.location([]).end()
+      })
 
       request(app)
         .get('/')
         .expect('Location', '')
         .expect(200, done)
-    });
+    })
 
-    it('should consistently handle empty string input', function (done) {
-      var app = express()
-      app.use(function (req, res) {
-        res.location('').end();
-      });
+    it('should consistently handle empty string input', (done) => {
+      const app = express()
+      app.use((req, res) => {
+        res.location('').end()
+      })
 
       request(app)
         .get('/')
         .expect('Location', '')
         .expect(200, done)
-    });
-
+    })
 
     if (typeof URL !== 'undefined') {
-      it('should accept an instance of URL', function (done) {
-        var app = express();
+      it('should accept an instance of URL', (done) => {
+        const app = express()
 
-        app.use(function(req, res){
-          res.location(new URL('http://google.com/')).end();
-        });
+        app.use((req, res) => {
+          res.location(new URL('http://google.com/')).end()
+        })
 
         request(app)
           .get('/')
           .expect('Location', 'http://google.com/')
-          .expect(200, done);
-      });
+          .expect(200, done)
+      })
     }
   })
 
-  describe('location header encoding', function() {
+  describe('location header encoding', () => {
+    /* eslint-disable n/no-deprecated-api */
     function createRedirectServerForDomain (domain) {
-      var app = express();
-      app.use(function (req, res) {
-        var host = url.parse(req.query.q, false, true).host;
+      const app = express()
+      app.use((req, res) => {
+        const host = url.parse(req.query.q, false, true).host
         // This is here to show a basic check one might do which
         // would pass but then the location header would still be bad
         if (host !== domain) {
-          res.status(400).end('Bad host: ' + host + ' !== ' + domain);
+          res.status(400).end('Bad host: ' + host + ' !== ' + domain)
         }
-        res.location(req.query.q).end();
-      });
-      return app;
+        res.location(req.query.q).end()
+      })
+      return app
     }
 
     function testRequestedRedirect (app, inputUrl, expected, expectedHost, done) {
@@ -159,158 +159,158 @@ describe('res', function(){
         .expect('') // No body.
         .expect(200)
         .expect('Location', expected)
-        .end(function (err, res) {
+        .end((err, res) => {
           if (err) {
             console.log('headers:', res.headers)
-            console.error('error', res.error, err);
-            return done(err, res);
+            console.error('error', res.error, err)
+            return done(err, res)
           }
 
           // Parse the hosts from the input URL and the Location header
-          var inputHost = url.parse(inputUrl, false, true).host;
-          var locationHost = url.parse(res.headers['location'], false, true).host;
+          const inputHost = url.parse(inputUrl, false, true).host
+          const locationHost = url.parse(res.headers['location'], false, true).host
 
-          assert.strictEqual(locationHost, expectedHost);
+          assert.strictEqual(locationHost, expectedHost)
 
           // Assert that the hosts are the same
           if (inputHost !== locationHost) {
-            return done(new Error('Hosts do not match: ' + inputHost + " !== " +  locationHost));
+            return done(new Error('Hosts do not match: ' + inputHost + ' !== ' + locationHost))
           }
 
-          return done(null, res);
-        });
+          return done(null, res)
+        })
     }
 
-    it('should not touch already-encoded sequences in "url"', function (done) {
-      var app = createRedirectServerForDomain('google.com');
+    it('should not touch already-encoded sequences in "url"', (done) => {
+      const app = createRedirectServerForDomain('google.com')
       testRequestedRedirect(
         app,
         'https://google.com?q=%A710',
         'https://google.com?q=%A710',
         'google.com',
         done
-      );
-    });
+      )
+    })
 
-    it('should consistently handle relative urls', function (done) {
-      var app = createRedirectServerForDomain(null);
+    it('should consistently handle relative urls', (done) => {
+      const app = createRedirectServerForDomain(null)
       testRequestedRedirect(
         app,
         '/foo/bar',
         '/foo/bar',
         null,
         done
-      );
-    });
+      )
+    })
 
-    it('should not encode urls in such a way that they can bypass redirect allow lists', function (done) {
-      var app = createRedirectServerForDomain('google.com');
+    it('should not encode urls in such a way that they can bypass redirect allow lists', (done) => {
+      const app = createRedirectServerForDomain('google.com')
       testRequestedRedirect(
         app,
         'http://google.com\\@apple.com',
         'http://google.com\\@apple.com',
         'google.com',
         done
-      );
-    });
+      )
+    })
 
-    it('should not be case sensitive', function (done) {
-      var app = createRedirectServerForDomain('google.com');
+    it('should not be case sensitive', (done) => {
+      const app = createRedirectServerForDomain('google.com')
       testRequestedRedirect(
         app,
         'HTTP://google.com\\@apple.com',
         'HTTP://google.com\\@apple.com',
         'google.com',
         done
-      );
-    });
+      )
+    })
 
-    it('should work with https', function (done) {
-      var app = createRedirectServerForDomain('google.com');
+    it('should work with https', (done) => {
+      const app = createRedirectServerForDomain('google.com')
       testRequestedRedirect(
         app,
         'https://google.com\\@apple.com',
         'https://google.com\\@apple.com',
         'google.com',
         done
-      );
-    });
+      )
+    })
 
-    it('should correctly encode schemaless paths', function (done) {
-      var app = createRedirectServerForDomain('google.com');
+    it('should correctly encode schemaless paths', (done) => {
+      const app = createRedirectServerForDomain('google.com')
       testRequestedRedirect(
         app,
         '//google.com\\@apple.com/',
         '//google.com\\@apple.com/',
         'google.com',
         done
-      );
-    });
+      )
+    })
 
-    it('should keep backslashes in the path', function (done) {
-      var app = createRedirectServerForDomain('google.com');
+    it('should keep backslashes in the path', (done) => {
+      const app = createRedirectServerForDomain('google.com')
       testRequestedRedirect(
         app,
         'https://google.com/foo\\bar\\baz',
         'https://google.com/foo\\bar\\baz',
         'google.com',
         done
-      );
-    });
+      )
+    })
 
-    it('should escape header splitting for old node versions', function (done) {
-      var app = createRedirectServerForDomain('google.com');
+    it('should escape header splitting for old node versions', (done) => {
+      const app = createRedirectServerForDomain('google.com')
       testRequestedRedirect(
         app,
         'http://google.com\\@apple.com/%0d%0afoo:%20bar',
         'http://google.com\\@apple.com/%0d%0afoo:%20bar',
         'google.com',
         done
-      );
-    });
+      )
+    })
 
-    it('should encode unicode correctly', function (done) {
-      var app = createRedirectServerForDomain(null);
+    it('should encode unicode correctly', (done) => {
+      const app = createRedirectServerForDomain(null)
       testRequestedRedirect(
         app,
         '/%e2%98%83',
         '/%e2%98%83',
         null,
         done
-      );
-    });
+      )
+    })
 
-    it('should encode unicode correctly even with a bad host', function (done) {
-      var app = createRedirectServerForDomain('google.com');
+    it('should encode unicode correctly even with a bad host', (done) => {
+      const app = createRedirectServerForDomain('google.com')
       testRequestedRedirect(
         app,
         'http://google.com\\@apple.com/%e2%98%83',
         'http://google.com\\@apple.com/%e2%98%83',
         'google.com',
         done
-      );
-    });
+      )
+    })
 
-    it('should work correctly despite using deprecated url.parse', function (done) {
-      var app = createRedirectServerForDomain('google.com');
+    it('should work correctly despite using deprecated url.parse', (done) => {
+      const app = createRedirectServerForDomain('google.com')
       testRequestedRedirect(
         app,
         'https://google.com\'.bb.com/1.html',
         'https://google.com\'.bb.com/1.html',
         'google.com',
         done
-      );
-    });
+      )
+    })
 
-    it('should encode file uri path', function (done) {
-      var app = createRedirectServerForDomain('');
+    it('should encode file uri path', (done) => {
+      const app = createRedirectServerForDomain('')
       testRequestedRedirect(
         app,
         'file:///etc\\passwd',
         'file:///etc\\passwd',
         '',
         done
-      );
-    });
-  });
+      )
+    })
+  })
 })
diff --git a/test/res.redirect.js b/test/res.redirect.js
index 264e0f2b8f3..5adeb0c98b6 100644
--- a/test/res.redirect.js
+++ b/test/res.redirect.js
@@ -1,73 +1,73 @@
 'use strict'
 
-var express = require('..');
-var request = require('supertest');
-var utils = require('./support/utils');
+const express = require('../')
+const request = require('supertest')
+const utils = require('./support/utils')
 
-describe('res', function(){
-  describe('.redirect(url)', function(){
-    it('should default to a 302 redirect', function(done){
-      var app = express();
+describe('res', () => {
+  describe('.redirect(url)', () => {
+    it('should default to a 302 redirect', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect('http://google.com');
-      });
+      app.use((req, res) => {
+        res.redirect('http://google.com')
+      })
 
       request(app)
-      .get('/')
-      .expect('location', 'http://google.com')
-      .expect(302, done)
+        .get('/')
+        .expect('location', 'http://google.com')
+        .expect(302, done)
     })
 
-    it('should encode "url"', function (done) {
-      var app = express()
+    it('should encode "url"', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.redirect('https://google.com?q=\u2603 §10')
       })
 
       request(app)
-      .get('/')
-      .expect('Location', 'https://google.com?q=%E2%98%83%20%C2%A710')
-      .expect(302, done)
+        .get('/')
+        .expect('Location', 'https://google.com?q=%E2%98%83%20%C2%A710')
+        .expect(302, done)
     })
 
-    it('should not touch already-encoded sequences in "url"', function (done) {
-      var app = express()
+    it('should not touch already-encoded sequences in "url"', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.redirect('https://google.com?q=%A710')
       })
 
       request(app)
-      .get('/')
-      .expect('Location', 'https://google.com?q=%A710')
-      .expect(302, done)
+        .get('/')
+        .expect('Location', 'https://google.com?q=%A710')
+        .expect(302, done)
     })
   })
 
-  describe('.redirect(status, url)', function(){
-    it('should set the response status', function(done){
-      var app = express();
+  describe('.redirect(status, url)', () => {
+    it('should set the response status', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect(303, 'http://google.com');
-      });
+      app.use((req, res) => {
+        res.redirect(303, 'http://google.com')
+      })
 
       request(app)
-      .get('/')
-      .expect('Location', 'http://google.com')
-      .expect(303, done)
+        .get('/')
+        .expect('Location', 'http://google.com')
+        .expect(303, done)
     })
   })
 
-  describe('when the request method is HEAD', function(){
-    it('should ignore the body', function(done){
-      var app = express();
+  describe('when the request method is HEAD', () => {
+    it('should ignore the body', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect('http://google.com');
-      });
+      app.use((req, res) => {
+        res.redirect('http://google.com')
+      })
 
       request(app)
         .head('/')
@@ -78,127 +78,127 @@ describe('res', function(){
     })
   })
 
-  describe('when accepting html', function(){
-    it('should respond with html', function(done){
-      var app = express();
+  describe('when accepting html', () => {
+    it('should respond with html', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect('http://google.com');
-      });
+      app.use((req, res) => {
+        res.redirect('http://google.com')
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', 'text/html')
-      .expect('Content-Type', /html/)
-      .expect('Location', 'http://google.com')
-      .expect(302, '<p>Found. Redirecting to http://google.com</p>', done)
+        .get('/')
+        .set('Accept', 'text/html')
+        .expect('Content-Type', /html/)
+        .expect('Location', 'http://google.com')
+        .expect(302, '<p>Found. Redirecting to http://google.com</p>', done)
     })
 
-    it('should escape the url', function(done){
-      var app = express();
+    it('should escape the url', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect('<la\'me>');
-      });
+      app.use((req, res) => {
+        res.redirect('<la\'me>')
+      })
 
       request(app)
-      .get('/')
-      .set('Host', 'http://example.com')
-      .set('Accept', 'text/html')
-      .expect('Content-Type', /html/)
-      .expect('Location', '%3Cla\'me%3E')
-      .expect(302, '<p>Found. Redirecting to %3Cla&#39;me%3E</p>', done)
+        .get('/')
+        .set('Host', 'http://example.com')
+        .set('Accept', 'text/html')
+        .expect('Content-Type', /html/)
+        .expect('Location', '%3Cla\'me%3E')
+        .expect(302, '<p>Found. Redirecting to %3Cla&#39;me%3E</p>', done)
     })
 
-    it('should not render evil javascript links in anchor href (prevent XSS)', function(done){
-      var app = express();
-      var xss = 'javascript:eval(document.body.innerHTML=`<p>XSS</p>`);';
-      var encodedXss = 'javascript:eval(document.body.innerHTML=%60%3Cp%3EXSS%3C/p%3E%60);';
+    it('should not render evil javascript links in anchor href (prevent XSS)', (done) => {
+      const app = express()
+      const xss = 'javascript:eval(document.body.innerHTML=`<p>XSS</p>`);'
+      const encodedXss = 'javascript:eval(document.body.innerHTML=%60%3Cp%3EXSS%3C/p%3E%60);'
 
-      app.use(function(req, res){
-        res.redirect(xss);
-      });
+      app.use((req, res) => {
+        res.redirect(xss)
+      })
 
       request(app)
-      .get('/')
-      .set('Host', 'http://example.com')
-      .set('Accept', 'text/html')
-      .expect('Content-Type', /html/)
-      .expect('Location', encodedXss)
-      .expect(302, '<p>Found. Redirecting to ' + encodedXss +'</p>', done);
-    });
+        .get('/')
+        .set('Host', 'http://example.com')
+        .set('Accept', 'text/html')
+        .expect('Content-Type', /html/)
+        .expect('Location', encodedXss)
+        .expect(302, '<p>Found. Redirecting to ' + encodedXss + '</p>', done)
+    })
 
-    it('should include the redirect type', function(done){
-      var app = express();
+    it('should include the redirect type', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect(301, 'http://google.com');
-      });
+      app.use((req, res) => {
+        res.redirect(301, 'http://google.com')
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', 'text/html')
-      .expect('Content-Type', /html/)
-      .expect('Location', 'http://google.com')
-      .expect(301, '<p>Moved Permanently. Redirecting to http://google.com</p>', done);
+        .get('/')
+        .set('Accept', 'text/html')
+        .expect('Content-Type', /html/)
+        .expect('Location', 'http://google.com')
+        .expect(301, '<p>Moved Permanently. Redirecting to http://google.com</p>', done)
     })
   })
 
-  describe('when accepting text', function(){
-    it('should respond with text', function(done){
-      var app = express();
+  describe('when accepting text', () => {
+    it('should respond with text', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect('http://google.com');
-      });
+      app.use((req, res) => {
+        res.redirect('http://google.com')
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', 'text/plain, */*')
-      .expect('Content-Type', /plain/)
-      .expect('Location', 'http://google.com')
-      .expect(302, 'Found. Redirecting to http://google.com', done)
+        .get('/')
+        .set('Accept', 'text/plain, */*')
+        .expect('Content-Type', /plain/)
+        .expect('Location', 'http://google.com')
+        .expect(302, 'Found. Redirecting to http://google.com', done)
     })
 
-    it('should encode the url', function(done){
-      var app = express();
+    it('should encode the url', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect('http://example.com/?param=<script>alert("hax");</script>');
-      });
+      app.use((req, res) => {
+        res.redirect('http://example.com/?param=<script>alert("hax");</script>')
+      })
 
       request(app)
-      .get('/')
-      .set('Host', 'http://example.com')
-      .set('Accept', 'text/plain, */*')
-      .expect('Content-Type', /plain/)
-      .expect('Location', 'http://example.com/?param=%3Cscript%3Ealert(%22hax%22);%3C/script%3E')
-      .expect(302, 'Found. Redirecting to http://example.com/?param=%3Cscript%3Ealert(%22hax%22);%3C/script%3E', done)
+        .get('/')
+        .set('Host', 'http://example.com')
+        .set('Accept', 'text/plain, */*')
+        .expect('Content-Type', /plain/)
+        .expect('Location', 'http://example.com/?param=%3Cscript%3Ealert(%22hax%22);%3C/script%3E')
+        .expect(302, 'Found. Redirecting to http://example.com/?param=%3Cscript%3Ealert(%22hax%22);%3C/script%3E', done)
     })
 
-    it('should include the redirect type', function(done){
-      var app = express();
+    it('should include the redirect type', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect(301, 'http://google.com');
-      });
+      app.use((req, res) => {
+        res.redirect(301, 'http://google.com')
+      })
 
       request(app)
-      .get('/')
-      .set('Accept', 'text/plain, */*')
-      .expect('Content-Type', /plain/)
-      .expect('Location', 'http://google.com')
-      .expect(301, 'Moved Permanently. Redirecting to http://google.com', done);
+        .get('/')
+        .set('Accept', 'text/plain, */*')
+        .expect('Content-Type', /plain/)
+        .expect('Location', 'http://google.com')
+        .expect(301, 'Moved Permanently. Redirecting to http://google.com', done)
     })
   })
 
-  describe('when accepting neither text or html', function(){
-    it('should respond with an empty body', function(done){
-      var app = express();
+  describe('when accepting neither text or html', () => {
+    it('should respond with an empty body', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.redirect('http://google.com');
-      });
+      app.use((req, res) => {
+        res.redirect('http://google.com')
+      })
 
       request(app)
         .get('/')
diff --git a/test/res.render.js b/test/res.render.js
index 114b398e0b4..9fc7d1362e3 100644
--- a/test/res.render.js
+++ b/test/res.render.js
@@ -1,367 +1,367 @@
 'use strict'
 
-var express = require('..');
-var path = require('node:path')
-var request = require('supertest');
-var tmpl = require('./support/tmpl');
+const express = require('../')
+const path = require('node:path')
+const request = require('supertest')
+const tmpl = require('./support/tmpl')
 
-describe('res', function(){
-  describe('.render(name)', function(){
-    it('should support absolute paths', function(done){
-      var app = createApp();
+describe('res', () => {
+  describe('.render(name)', () => {
+    it('should support absolute paths', (done) => {
+      const app = createApp()
 
-      app.locals.user = { name: 'tobi' };
+      app.locals.user = { name: 'tobi' }
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.render(path.join(__dirname, 'fixtures', 'user.tmpl'))
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>tobi</p>', done);
+        .get('/')
+        .expect('<p>tobi</p>', done)
     })
 
-    it('should support absolute paths with "view engine"', function(done){
-      var app = createApp();
+    it('should support absolute paths with "view engine"', (done) => {
+      const app = createApp()
 
-      app.locals.user = { name: 'tobi' };
-      app.set('view engine', 'tmpl');
+      app.locals.user = { name: 'tobi' }
+      app.set('view engine', 'tmpl')
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.render(path.join(__dirname, 'fixtures', 'user'))
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>tobi</p>', done);
+        .get('/')
+        .expect('<p>tobi</p>', done)
     })
 
-    it('should error without "view engine" set and file extension to a non-engine module', function (done) {
-      var app = createApp()
+    it('should error without "view engine" set and file extension to a non-engine module', (done) => {
+      const app = createApp()
 
       app.locals.user = { name: 'tobi' }
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.render(path.join(__dirname, 'fixtures', 'broken.send'))
       })
 
       request(app)
-      .get('/')
-      .expect(500, /does not provide a view engine/, done)
+        .get('/')
+        .expect(500, /does not provide a view engine/, done)
     })
 
-    it('should error without "view engine" set and no file extension', function (done) {
-      var app = createApp();
+    it('should error without "view engine" set and no file extension', (done) => {
+      const app = createApp()
 
-      app.locals.user = { name: 'tobi' };
+      app.locals.user = { name: 'tobi' }
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.render(path.join(__dirname, 'fixtures', 'user'))
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect(500, /No default engine was specified/, done);
+        .get('/')
+        .expect(500, /No default engine was specified/, done)
     })
 
-    it('should expose app.locals', function(done){
-      var app = createApp();
+    it('should expose app.locals', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.locals.user = { name: 'tobi' };
+      app.locals.user = { name: 'tobi' }
 
-      app.use(function(req, res){
-        res.render('user.tmpl');
-      });
+      app.use((req, res) => {
+        res.render('user.tmpl')
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>tobi</p>', done);
+        .get('/')
+        .expect('<p>tobi</p>', done)
     })
 
-    it('should expose app.locals with `name` property', function(done){
-      var app = createApp();
+    it('should expose app.locals with `name` property', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.locals.name = 'tobi';
+      app.locals.name = 'tobi'
 
-      app.use(function(req, res){
-        res.render('name.tmpl');
-      });
+      app.use((req, res) => {
+        res.render('name.tmpl')
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>tobi</p>', done);
+        .get('/')
+        .expect('<p>tobi</p>', done)
     })
 
-    it('should support index.<engine>', function(done){
-      var app = createApp();
+    it('should support index.<engine>', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.set('view engine', 'tmpl');
+      app.set('view engine', 'tmpl')
 
-      app.use(function(req, res){
-        res.render('blog/post');
-      });
+      app.use((req, res) => {
+        res.render('blog/post')
+      })
 
       request(app)
-      .get('/')
-      .expect('<h1>blog post</h1>', done);
+        .get('/')
+        .expect('<h1>blog post</h1>', done)
     })
 
-    describe('when an error occurs', function(){
-      it('should next(err)', function(done){
-        var app = createApp();
+    describe('when an error occurs', () => {
+      it('should next(err)', (done) => {
+        const app = createApp()
 
         app.set('views', path.join(__dirname, 'fixtures'))
 
-        app.use(function(req, res){
-          res.render('user.tmpl');
-        });
+        app.use((req, res) => {
+          res.render('user.tmpl')
+        })
 
-        app.use(function(err, req, res, next){
+        app.use((err, req, res, next) => {
           res.status(500).send('got error: ' + err.name)
-        });
+        })
 
         request(app)
-        .get('/')
-        .expect(500, 'got error: RenderError', done)
+          .get('/')
+          .expect(500, 'got error: RenderError', done)
       })
     })
 
-    describe('when "view engine" is given', function(){
-      it('should render the template', function(done){
-        var app = createApp();
+    describe('when "view engine" is given', () => {
+      it('should render the template', (done) => {
+        const app = createApp()
 
-        app.set('view engine', 'tmpl');
+        app.set('view engine', 'tmpl')
         app.set('views', path.join(__dirname, 'fixtures'))
 
-        app.use(function(req, res){
-          res.render('email');
-        });
+        app.use((req, res) => {
+          res.render('email')
+        })
 
         request(app)
-        .get('/')
-        .expect('<p>This is an email</p>', done);
+          .get('/')
+          .expect('<p>This is an email</p>', done)
       })
     })
 
-    describe('when "views" is given', function(){
-      it('should lookup the file in the path', function(done){
-        var app = createApp();
+    describe('when "views" is given', () => {
+      it('should lookup the file in the path', (done) => {
+        const app = createApp()
 
         app.set('views', path.join(__dirname, 'fixtures', 'default_layout'))
 
-        app.use(function(req, res){
-          res.render('user.tmpl', { user: { name: 'tobi' } });
-        });
+        app.use((req, res) => {
+          res.render('user.tmpl', { user: { name: 'tobi' } })
+        })
 
         request(app)
-        .get('/')
-        .expect('<p>tobi</p>', done);
+          .get('/')
+          .expect('<p>tobi</p>', done)
       })
 
-      describe('when array of paths', function(){
-        it('should lookup the file in the path', function(done){
-          var app = createApp();
-          var views = [
+      describe('when array of paths', () => {
+        it('should lookup the file in the path', (done) => {
+          const app = createApp()
+          const views = [
             path.join(__dirname, 'fixtures', 'local_layout'),
             path.join(__dirname, 'fixtures', 'default_layout')
           ]
 
-          app.set('views', views);
+          app.set('views', views)
 
-          app.use(function(req, res){
-            res.render('user.tmpl', { user: { name: 'tobi' } });
-          });
+          app.use((req, res) => {
+            res.render('user.tmpl', { user: { name: 'tobi' } })
+          })
 
           request(app)
-          .get('/')
-          .expect('<span>tobi</span>', done);
+            .get('/')
+            .expect('<span>tobi</span>', done)
         })
 
-        it('should lookup in later paths until found', function(done){
-          var app = createApp();
-          var views = [
+        it('should lookup in later paths until found', (done) => {
+          const app = createApp()
+          const views = [
             path.join(__dirname, 'fixtures', 'local_layout'),
             path.join(__dirname, 'fixtures', 'default_layout')
           ]
 
-          app.set('views', views);
+          app.set('views', views)
 
-          app.use(function(req, res){
-            res.render('name.tmpl', { name: 'tobi' });
-          });
+          app.use((req, res) => {
+            res.render('name.tmpl', { name: 'tobi' })
+          })
 
           request(app)
-          .get('/')
-          .expect('<p>tobi</p>', done);
+            .get('/')
+            .expect('<p>tobi</p>', done)
         })
       })
     })
   })
 
-  describe('.render(name, option)', function(){
-    it('should render the template', function(done){
-      var app = createApp();
+  describe('.render(name, option)', () => {
+    it('should render the template', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
 
-      var user = { name: 'tobi' };
+      const user = { name: 'tobi' }
 
-      app.use(function(req, res){
-        res.render('user.tmpl', { user: user });
-      });
+      app.use((req, res) => {
+        res.render('user.tmpl', { user })
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>tobi</p>', done);
+        .get('/')
+        .expect('<p>tobi</p>', done)
     })
 
-    it('should expose app.locals', function(done){
-      var app = createApp();
+    it('should expose app.locals', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.locals.user = { name: 'tobi' };
+      app.locals.user = { name: 'tobi' }
 
-      app.use(function(req, res){
-        res.render('user.tmpl');
-      });
+      app.use((req, res) => {
+        res.render('user.tmpl')
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>tobi</p>', done);
+        .get('/')
+        .expect('<p>tobi</p>', done)
     })
 
-    it('should expose res.locals', function(done){
-      var app = createApp();
+    it('should expose res.locals', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
 
-      app.use(function(req, res){
-        res.locals.user = { name: 'tobi' };
-        res.render('user.tmpl');
-      });
+      app.use((req, res) => {
+        res.locals.user = { name: 'tobi' }
+        res.render('user.tmpl')
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>tobi</p>', done);
+        .get('/')
+        .expect('<p>tobi</p>', done)
     })
 
-    it('should give precedence to res.locals over app.locals', function(done){
-      var app = createApp();
+    it('should give precedence to res.locals over app.locals', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.locals.user = { name: 'tobi' };
+      app.locals.user = { name: 'tobi' }
 
-      app.use(function(req, res){
-        res.locals.user = { name: 'jane' };
-        res.render('user.tmpl', {});
-      });
+      app.use((req, res) => {
+        res.locals.user = { name: 'jane' }
+        res.render('user.tmpl', {})
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>jane</p>', done);
+        .get('/')
+        .expect('<p>jane</p>', done)
     })
 
-    it('should give precedence to res.render() locals over res.locals', function(done){
-      var app = createApp();
+    it('should give precedence to res.render() locals over res.locals', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      var jane = { name: 'jane' };
+      const jane = { name: 'jane' }
 
-      app.use(function(req, res){
-        res.locals.user = { name: 'tobi' };
-        res.render('user.tmpl', { user: jane });
-      });
+      app.use((req, res) => {
+        res.locals.user = { name: 'tobi' }
+        res.render('user.tmpl', { user: jane })
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>jane</p>', done);
+        .get('/')
+        .expect('<p>jane</p>', done)
     })
 
-    it('should give precedence to res.render() locals over app.locals', function(done){
-      var app = createApp();
+    it('should give precedence to res.render() locals over app.locals', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
-      app.locals.user = { name: 'tobi' };
-      var jane = { name: 'jane' };
+      app.locals.user = { name: 'tobi' }
+      const jane = { name: 'jane' }
 
-      app.use(function(req, res){
-        res.render('user.tmpl', { user: jane });
-      });
+      app.use((req, res) => {
+        res.render('user.tmpl', { user: jane })
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>jane</p>', done);
+        .get('/')
+        .expect('<p>jane</p>', done)
     })
   })
 
-  describe('.render(name, options, fn)', function(){
-    it('should pass the resulting string', function(done){
-      var app = createApp();
+  describe('.render(name, options, fn)', () => {
+    it('should pass the resulting string', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
 
-      app.use(function(req, res){
-        var tobi = { name: 'tobi' };
-        res.render('user.tmpl', { user: tobi }, function (err, html) {
-          html = html.replace('tobi', 'loki');
-          res.end(html);
-        });
-      });
+      app.use((req, res) => {
+        const tobi = { name: 'tobi' }
+        res.render('user.tmpl', { user: tobi }, (err, html) => {
+          html = html.replace('tobi', 'loki')
+          res.end(html)
+        })
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>loki</p>', done);
+        .get('/')
+        .expect('<p>loki</p>', done)
     })
   })
 
-  describe('.render(name, fn)', function(){
-    it('should pass the resulting string', function(done){
-      var app = createApp();
+  describe('.render(name, fn)', () => {
+    it('should pass the resulting string', (done) => {
+      const app = createApp()
 
       app.set('views', path.join(__dirname, 'fixtures'))
 
-      app.use(function(req, res){
-        res.locals.user = { name: 'tobi' };
-        res.render('user.tmpl', function (err, html) {
-          html = html.replace('tobi', 'loki');
-          res.end(html);
-        });
-      });
+      app.use((req, res) => {
+        res.locals.user = { name: 'tobi' }
+        res.render('user.tmpl', (err, html) => {
+          html = html.replace('tobi', 'loki')
+          res.end(html)
+        })
+      })
 
       request(app)
-      .get('/')
-      .expect('<p>loki</p>', done);
+        .get('/')
+        .expect('<p>loki</p>', done)
     })
 
-    describe('when an error occurs', function(){
-      it('should pass it to the callback', function(done){
-        var app = createApp();
+    describe('when an error occurs', () => {
+      it('should pass it to the callback', (done) => {
+        const app = createApp()
 
         app.set('views', path.join(__dirname, 'fixtures'))
 
-        app.use(function(req, res){
-          res.render('user.tmpl', function (err) {
+        app.use((req, res) => {
+          res.render('user.tmpl', (err) => {
             if (err) {
               res.status(500).send('got error: ' + err.name)
             }
-          });
-        });
+          })
+        })
 
         request(app)
-        .get('/')
-        .expect(500, 'got error: RenderError', done)
+          .get('/')
+          .expect(500, 'got error: RenderError', done)
       })
     })
   })
 })
 
-function createApp() {
-  var app = express();
+function createApp () {
+  const app = express()
 
-  app.engine('.tmpl', tmpl);
+  app.engine('.tmpl', tmpl)
 
-  return app;
+  return app
 }
diff --git a/test/res.send.js b/test/res.send.js
index 8547b77648b..7cfec26d782 100644
--- a/test/res.send.js
+++ b/test/res.send.js
@@ -1,148 +1,148 @@
 'use strict'
 
-var assert = require('node:assert')
-const { Buffer } = require('node:buffer');
-var express = require('..');
-var methods = require('../lib/utils').methods;
-var request = require('supertest');
-var utils = require('./support/utils');
-
-var shouldSkipQuery = require('./support/utils').shouldSkipQuery
-
-describe('res', function(){
-  describe('.send()', function(){
-    it('should set body to ""', function(done){
-      var app = express();
-
-      app.use(function(req, res){
-        res.send();
-      });
+const assert = require('node:assert')
+const { Buffer } = require('node:buffer')
+const express = require('../')
+const { methods } = require('../lib/utils')
+const request = require('supertest')
+const utils = require('./support/utils')
+
+const { shouldSkipQuery } = require('./support/utils')
+
+describe('res', () => {
+  describe('.send()', () => {
+    it('should set body to ""', (done) => {
+      const app = express()
+
+      app.use((req, res) => {
+        res.send()
+      })
 
       request(app)
-      .get('/')
-      .expect(200, '', done);
+        .get('/')
+        .expect(200, '', done)
     })
   })
 
-  describe('.send(null)', function(){
-    it('should set body to ""', function(done){
-      var app = express();
+  describe('.send(null)', () => {
+    it('should set body to ""', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.send(null);
-      });
+      app.use((req, res) => {
+        res.send(null)
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Length', '0')
-      .expect(200, '', done);
+        .get('/')
+        .expect('Content-Length', '0')
+        .expect(200, '', done)
     })
   })
 
-  describe('.send(undefined)', function(){
-    it('should set body to ""', function(done){
-      var app = express();
+  describe('.send(undefined)', () => {
+    it('should set body to ""', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.send(undefined);
-      });
+      app.use((req, res) => {
+        res.send(undefined)
+      })
 
       request(app)
-      .get('/')
-      .expect(200, '', done);
+        .get('/')
+        .expect(200, '', done)
     })
   })
 
-  describe('.send(Number)', function(){
-    it('should send as application/json', function(done){
-      var app = express();
+  describe('.send(Number)', () => {
+    it('should send as application/json', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.send(1000);
-      });
+      app.use((req, res) => {
+        res.send(1000)
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'application/json; charset=utf-8')
-      .expect(200, '1000', done)
+        .get('/')
+        .expect('Content-Type', 'application/json; charset=utf-8')
+        .expect(200, '1000', done)
     })
   })
 
-  describe('.send(String)', function(){
-    it('should send as html', function(done){
-      var app = express();
+  describe('.send(String)', () => {
+    it('should send as html', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.send('<p>hey</p>');
-      });
+      app.use((req, res) => {
+        res.send('<p>hey</p>')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/html; charset=utf-8')
-      .expect(200, '<p>hey</p>', done);
+        .get('/')
+        .expect('Content-Type', 'text/html; charset=utf-8')
+        .expect(200, '<p>hey</p>', done)
     })
 
-    it('should set ETag', function (done) {
-      var app = express();
+    it('should set ETag', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        var str = Array(1000).join('-');
-        res.send(str);
-      });
+      app.use((req, res) => {
+        const str = Array(1000).join('-')
+        res.send(str)
+      })
 
       request(app)
-      .get('/')
-      .expect('ETag', 'W/"3e7-qPnkJ3CVdVhFJQvUBfF10TmVA7g"')
-      .expect(200, done);
+        .get('/')
+        .expect('ETag', 'W/"3e7-qPnkJ3CVdVhFJQvUBfF10TmVA7g"')
+        .expect(200, done)
     })
 
-    it('should not override Content-Type', function(done){
-      var app = express();
+    it('should not override Content-Type', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.set('Content-Type', 'text/plain').send('hey');
-      });
+      app.use((req, res) => {
+        res.set('Content-Type', 'text/plain').send('hey')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/plain; charset=utf-8')
-      .expect(200, 'hey', done);
+        .get('/')
+        .expect('Content-Type', 'text/plain; charset=utf-8')
+        .expect(200, 'hey', done)
     })
 
-    it('should override charset in Content-Type', function(done){
-      var app = express();
+    it('should override charset in Content-Type', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.set('Content-Type', 'text/plain; charset=iso-8859-1').send('hey');
-      });
+      app.use((req, res) => {
+        res.set('Content-Type', 'text/plain; charset=iso-8859-1').send('hey')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/plain; charset=utf-8')
-      .expect(200, 'hey', done);
+        .get('/')
+        .expect('Content-Type', 'text/plain; charset=utf-8')
+        .expect(200, 'hey', done)
     })
 
-    it('should keep charset in Content-Type for Buffers', function(done){
-      var app = express();
+    it('should keep charset in Content-Type for Buffers', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.set('Content-Type', 'text/plain; charset=iso-8859-1').send(Buffer.from('hi'))
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/plain; charset=iso-8859-1')
-      .expect(200, 'hi', done);
+        .get('/')
+        .expect('Content-Type', 'text/plain; charset=iso-8859-1')
+        .expect(200, 'hi', done)
     })
   })
 
-  describe('.send(Buffer)', function(){
-    it('should send as octet-stream', function(done){
-      var app = express();
+  describe('.send(Buffer)', () => {
+    it('should send as octet-stream', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.send(Buffer.from('hello'))
-      });
+      })
 
       request(app)
         .get('/')
@@ -152,81 +152,81 @@ describe('res', function(){
         .end(done)
     })
 
-    it('should set ETag', function (done) {
-      var app = express();
+    it('should set ETag', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.send(Buffer.alloc(999, '-'))
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect('ETag', 'W/"3e7-qPnkJ3CVdVhFJQvUBfF10TmVA7g"')
-      .expect(200, done);
+        .get('/')
+        .expect('ETag', 'W/"3e7-qPnkJ3CVdVhFJQvUBfF10TmVA7g"')
+        .expect(200, done)
     })
 
-    it('should not override Content-Type', function(done){
-      var app = express();
+    it('should not override Content-Type', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.set('Content-Type', 'text/plain').send(Buffer.from('hey'))
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/plain; charset=utf-8')
-      .expect(200, 'hey', done);
+        .get('/')
+        .expect('Content-Type', 'text/plain; charset=utf-8')
+        .expect(200, 'hey', done)
     })
 
-    it('should accept Uint8Array', function(done){
-      var app = express();
-      app.use(function(req, res){
-        const encodedHey = new TextEncoder().encode("hey");
-        res.set("Content-Type", "text/plain").send(encodedHey);
+    it('should accept Uint8Array', (done) => {
+      const app = express()
+      app.use((req, res) => {
+        const encodedHey = new TextEncoder().encode('hey')
+        res.set('Content-Type', 'text/plain').send(encodedHey)
       })
 
       request(app)
-        .get("/")
-        .expect("Content-Type", "text/plain; charset=utf-8")
-        .expect(200, "hey", done);
+        .get('/')
+        .expect('Content-Type', 'text/plain; charset=utf-8')
+        .expect(200, 'hey', done)
     })
 
-    it('should not override ETag', function (done) {
-      var app = express()
+    it('should not override ETag', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.type('text/plain').set('ETag', '"foo"').send(Buffer.from('hey'))
       })
 
       request(app)
-      .get('/')
-      .expect('ETag', '"foo"')
-      .expect(200, 'hey', done)
+        .get('/')
+        .expect('ETag', '"foo"')
+        .expect(200, 'hey', done)
     })
   })
 
-  describe('.send(Object)', function(){
-    it('should send as application/json', function(done){
-      var app = express();
+  describe('.send(Object)', () => {
+    it('should send as application/json', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.send({ name: 'tobi' });
-      });
+      app.use((req, res) => {
+        res.send({ name: 'tobi' })
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'application/json; charset=utf-8')
-      .expect(200, '{"name":"tobi"}', done)
+        .get('/')
+        .expect('Content-Type', 'application/json; charset=utf-8')
+        .expect(200, '{"name":"tobi"}', done)
     })
   })
 
-  describe('when the request method is HEAD', function(){
-    it('should ignore the body', function(done){
-      var app = express();
+  describe('when the request method is HEAD', () => {
+    it('should ignore the body', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.send('yay');
-      });
+      app.use((req, res) => {
+        res.send('yay')
+      })
 
       request(app)
         .head('/')
@@ -236,28 +236,28 @@ describe('res', function(){
     })
   })
 
-  describe('when .statusCode is 204', function(){
-    it('should strip Content-* fields, Transfer-Encoding field, and body', function(done){
-      var app = express();
+  describe('when .statusCode is 204', () => {
+    it('should strip Content-* fields, Transfer-Encoding field, and body', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.status(204).set('Transfer-Encoding', 'chunked').send('foo');
-      });
+      app.use((req, res) => {
+        res.status(204).set('Transfer-Encoding', 'chunked').send('foo')
+      })
 
       request(app)
-      .get('/')
-      .expect(utils.shouldNotHaveHeader('Content-Type'))
-      .expect(utils.shouldNotHaveHeader('Content-Length'))
-      .expect(utils.shouldNotHaveHeader('Transfer-Encoding'))
-      .expect(204, '', done);
+        .get('/')
+        .expect(utils.shouldNotHaveHeader('Content-Type'))
+        .expect(utils.shouldNotHaveHeader('Content-Length'))
+        .expect(utils.shouldNotHaveHeader('Transfer-Encoding'))
+        .expect(204, '', done)
     })
   })
 
-  describe('when .statusCode is 205', function () {
-    it('should strip Transfer-Encoding field and body, set Content-Length', function (done) {
-      var app = express()
+  describe('when .statusCode is 205', () => {
+    it('should strip Transfer-Encoding field and body, set Content-Length', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.status(205).set('Transfer-Encoding', 'chunked').send('foo')
       })
 
@@ -269,300 +269,297 @@ describe('res', function(){
     })
   })
 
-  describe('when .statusCode is 304', function(){
-    it('should strip Content-* fields, Transfer-Encoding field, and body', function(done){
-      var app = express();
+  describe('when .statusCode is 304', () => {
+    it('should strip Content-* fields, Transfer-Encoding field, and body', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.status(304).set('Transfer-Encoding', 'chunked').send('foo');
-      });
+      app.use((req, res) => {
+        res.status(304).set('Transfer-Encoding', 'chunked').send('foo')
+      })
 
       request(app)
-      .get('/')
-      .expect(utils.shouldNotHaveHeader('Content-Type'))
-      .expect(utils.shouldNotHaveHeader('Content-Length'))
-      .expect(utils.shouldNotHaveHeader('Transfer-Encoding'))
-      .expect(304, '', done);
+        .get('/')
+        .expect(utils.shouldNotHaveHeader('Content-Type'))
+        .expect(utils.shouldNotHaveHeader('Content-Length'))
+        .expect(utils.shouldNotHaveHeader('Transfer-Encoding'))
+        .expect(304, '', done)
     })
   })
 
-  it('should always check regardless of length', function(done){
-    var app = express();
-    var etag = '"asdf"';
+  it('should always check regardless of length', (done) => {
+    const app = express()
+    const etag = '"asdf"'
 
-    app.use(function(req, res, next){
-      res.set('ETag', etag);
-      res.send('hey');
-    });
+    app.use((req, res, next) => {
+      res.set('ETag', etag)
+      res.send('hey')
+    })
 
     request(app)
-    .get('/')
-    .set('If-None-Match', etag)
-    .expect(304, done);
+      .get('/')
+      .set('If-None-Match', etag)
+      .expect(304, done)
   })
 
-  it('should respond with 304 Not Modified when fresh', function(done){
-    var app = express();
-    var etag = '"asdf"';
+  it('should respond with 304 Not Modified when fresh', (done) => {
+    const app = express()
+    const etag = '"asdf"'
 
-    app.use(function(req, res){
-      var str = Array(1000).join('-');
-      res.set('ETag', etag);
-      res.send(str);
-    });
+    app.use((req, res) => {
+      const str = Array(1000).join('-')
+      res.set('ETag', etag)
+      res.send(str)
+    })
 
     request(app)
-    .get('/')
-    .set('If-None-Match', etag)
-    .expect(304, done);
+      .get('/')
+      .set('If-None-Match', etag)
+      .expect(304, done)
   })
 
-  it('should not perform freshness check unless 2xx or 304', function(done){
-    var app = express();
-    var etag = '"asdf"';
+  it('should not perform freshness check unless 2xx or 304', (done) => {
+    const app = express()
+    const etag = '"asdf"'
 
-    app.use(function(req, res, next){
-      res.status(500);
-      res.set('ETag', etag);
-      res.send('hey');
-    });
+    app.use((req, res, next) => {
+      res.status(500)
+      res.set('ETag', etag)
+      res.send('hey')
+    })
 
     request(app)
-    .get('/')
-    .set('If-None-Match', etag)
-    .expect('hey')
-    .expect(500, done);
+      .get('/')
+      .set('If-None-Match', etag)
+      .expect('hey')
+      .expect(500, done)
   })
 
-  it('should not support jsonp callbacks', function(done){
-    var app = express();
+  it('should not support jsonp callbacks', (done) => {
+    const app = express()
 
-    app.use(function(req, res){
-      res.send({ foo: 'bar' });
-    });
+    app.use((req, res) => {
+      res.send({ foo: 'bar' })
+    })
 
     request(app)
-    .get('/?callback=foo')
-    .expect('{"foo":"bar"}', done);
+      .get('/?callback=foo')
+      .expect('{"foo":"bar"}', done)
   })
 
-  it('should be chainable', function (done) {
-    var app = express()
+  it('should be chainable', (done) => {
+    const app = express()
 
-    app.use(function (req, res) {
+    app.use((req, res) => {
       assert.equal(res.send('hey'), res)
     })
 
     request(app)
-    .get('/')
-    .expect(200, 'hey', done)
+      .get('/')
+      .expect(200, 'hey', done)
   })
 
-  describe('"etag" setting', function () {
-    describe('when enabled', function () {
-      it('should send ETag', function (done) {
-        var app = express();
+  describe('"etag" setting', () => {
+    describe('when enabled', () => {
+      it('should send ETag', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.send('kajdslfkasdf');
-        });
+        app.use((req, res) => {
+          res.send('kajdslfkasdf')
+        })
 
-        app.enable('etag');
+        app.enable('etag')
 
         request(app)
-        .get('/')
-        .expect('ETag', 'W/"c-IgR/L5SF7CJQff4wxKGF/vfPuZ0"')
-        .expect(200, done);
-      });
+          .get('/')
+          .expect('ETag', 'W/"c-IgR/L5SF7CJQff4wxKGF/vfPuZ0"')
+          .expect(200, done)
+      })
 
-      methods.forEach(function (method) {
-        if (method === 'connect') return;
+      methods.forEach((method) => {
+        if (method === 'connect') return
 
         it('should send ETag in response to ' + method.toUpperCase() + ' request', function (done) {
           if (method === 'query' && shouldSkipQuery(process.versions.node)) {
             this.skip()
           }
-          var app = express();
+          const app = express()
 
-          app[method]('/', function (req, res) {
-            res.send('kajdslfkasdf');
-          });
+          app[method]('/', (req, res) => {
+            res.send('kajdslfkasdf')
+          })
 
-          request(app)
-          [method]('/')
-          .expect('ETag', 'W/"c-IgR/L5SF7CJQff4wxKGF/vfPuZ0"')
-          .expect(200, done);
+          request(app)[method]('/')
+            .expect('ETag', 'W/"c-IgR/L5SF7CJQff4wxKGF/vfPuZ0"')
+            .expect(200, done)
         })
-      });
+      })
 
-      it('should send ETag for empty string response', function (done) {
-        var app = express();
+      it('should send ETag for empty string response', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.send('');
-        });
+        app.use((req, res) => {
+          res.send('')
+        })
 
-        app.enable('etag');
+        app.enable('etag')
 
         request(app)
-        .get('/')
-        .expect('ETag', 'W/"0-2jmj7l5rSw0yVb/vlWAYkK/YBwk"')
-        .expect(200, done);
+          .get('/')
+          .expect('ETag', 'W/"0-2jmj7l5rSw0yVb/vlWAYkK/YBwk"')
+          .expect(200, done)
       })
 
-      it('should send ETag for long response', function (done) {
-        var app = express();
+      it('should send ETag for long response', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          var str = Array(1000).join('-');
-          res.send(str);
-        });
+        app.use((req, res) => {
+          const str = Array(1000).join('-')
+          res.send(str)
+        })
 
-        app.enable('etag');
+        app.enable('etag')
 
         request(app)
-        .get('/')
-        .expect('ETag', 'W/"3e7-qPnkJ3CVdVhFJQvUBfF10TmVA7g"')
-        .expect(200, done);
-      });
+          .get('/')
+          .expect('ETag', 'W/"3e7-qPnkJ3CVdVhFJQvUBfF10TmVA7g"')
+          .expect(200, done)
+      })
 
-      it('should not override ETag when manually set', function (done) {
-        var app = express();
+      it('should not override ETag when manually set', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.set('etag', '"asdf"');
-          res.send('hello!');
-        });
+        app.use((req, res) => {
+          res.set('etag', '"asdf"')
+          res.send('hello!')
+        })
 
-        app.enable('etag');
+        app.enable('etag')
 
         request(app)
-        .get('/')
-        .expect('ETag', '"asdf"')
-        .expect(200, done);
-      });
+          .get('/')
+          .expect('ETag', '"asdf"')
+          .expect(200, done)
+      })
 
-      it('should not send ETag for res.send()', function (done) {
-        var app = express();
+      it('should not send ETag for res.send()', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.send();
-        });
+        app.use((req, res) => {
+          res.send()
+        })
 
-        app.enable('etag');
+        app.enable('etag')
 
         request(app)
-        .get('/')
-        .expect(utils.shouldNotHaveHeader('ETag'))
-        .expect(200, done);
+          .get('/')
+          .expect(utils.shouldNotHaveHeader('ETag'))
+          .expect(200, done)
       })
-    });
+    })
 
-    describe('when disabled', function () {
-      it('should send no ETag', function (done) {
-        var app = express();
+    describe('when disabled', () => {
+      it('should send no ETag', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          var str = Array(1000).join('-');
-          res.send(str);
-        });
+        app.use((req, res) => {
+          const str = Array(1000).join('-')
+          res.send(str)
+        })
 
-        app.disable('etag');
+        app.disable('etag')
 
         request(app)
-        .get('/')
-        .expect(utils.shouldNotHaveHeader('ETag'))
-        .expect(200, done);
-      });
+          .get('/')
+          .expect(utils.shouldNotHaveHeader('ETag'))
+          .expect(200, done)
+      })
 
-      it('should send ETag when manually set', function (done) {
-        var app = express();
+      it('should send ETag when manually set', (done) => {
+        const app = express()
 
-        app.disable('etag');
+        app.disable('etag')
 
-        app.use(function (req, res) {
-          res.set('etag', '"asdf"');
-          res.send('hello!');
-        });
+        app.use((req, res) => {
+          res.set('etag', '"asdf"')
+          res.send('hello!')
+        })
 
         request(app)
-        .get('/')
-        .expect('ETag', '"asdf"')
-        .expect(200, done);
-      });
-    });
+          .get('/')
+          .expect('ETag', '"asdf"')
+          .expect(200, done)
+      })
+    })
 
-    describe('when "strong"', function () {
-      it('should send strong ETag', function (done) {
-        var app = express();
+    describe('when "strong"', () => {
+      it('should send strong ETag', (done) => {
+        const app = express()
 
-        app.set('etag', 'strong');
+        app.set('etag', 'strong')
 
-        app.use(function (req, res) {
-          res.send('hello, world!');
-        });
+        app.use((req, res) => {
+          res.send('hello, world!')
+        })
 
         request(app)
-        .get('/')
-        .expect('ETag', '"d-HwnTDHB9U/PRbFMN1z1wps51lqk"')
-        .expect(200, done);
+          .get('/')
+          .expect('ETag', '"d-HwnTDHB9U/PRbFMN1z1wps51lqk"')
+          .expect(200, done)
       })
     })
 
-    describe('when "weak"', function () {
-      it('should send weak ETag', function (done) {
-        var app = express();
+    describe('when "weak"', () => {
+      it('should send weak ETag', (done) => {
+        const app = express()
 
-        app.set('etag', 'weak');
+        app.set('etag', 'weak')
 
-        app.use(function (req, res) {
-          res.send('hello, world!');
-        });
+        app.use((req, res) => {
+          res.send('hello, world!')
+        })
 
         request(app)
-        .get('/')
-        .expect('ETag', 'W/"d-HwnTDHB9U/PRbFMN1z1wps51lqk"')
-        .expect(200, done)
+          .get('/')
+          .expect('ETag', 'W/"d-HwnTDHB9U/PRbFMN1z1wps51lqk"')
+          .expect(200, done)
       })
     })
 
-    describe('when a function', function () {
-      it('should send custom ETag', function (done) {
-        var app = express();
+    describe('when a function', () => {
+      it('should send custom ETag', (done) => {
+        const app = express()
 
-        app.set('etag', function (body, encoding) {
-          var chunk = !Buffer.isBuffer(body)
+        app.set('etag', (body, encoding) => {
+          const chunk = !Buffer.isBuffer(body)
             ? Buffer.from(body, encoding)
-            : body;
+            : body
           assert.strictEqual(chunk.toString(), 'hello, world!')
-          return '"custom"';
-        });
+          return '"custom"'
+        })
 
-        app.use(function (req, res) {
-          res.send('hello, world!');
-        });
+        app.use((req, res) => {
+          res.send('hello, world!')
+        })
 
         request(app)
-        .get('/')
-        .expect('ETag', '"custom"')
-        .expect(200, done);
+          .get('/')
+          .expect('ETag', '"custom"')
+          .expect(200, done)
       })
 
-      it('should not send falsy ETag', function (done) {
-        var app = express();
+      it('should not send falsy ETag', (done) => {
+        const app = express()
 
-        app.set('etag', function (body, encoding) {
-          return undefined;
-        });
+        app.set('etag', (body, encoding) => undefined)
 
-        app.use(function (req, res) {
-          res.send('hello, world!');
-        });
+        app.use((req, res) => {
+          res.send('hello, world!')
+        })
 
         request(app)
-        .get('/')
-        .expect(utils.shouldNotHaveHeader('ETag'))
-        .expect(200, done);
+          .get('/')
+          .expect(utils.shouldNotHaveHeader('ETag'))
+          .expect(200, done)
       })
     })
   })
diff --git a/test/res.sendFile.js b/test/res.sendFile.js
index 16eea79761e..ba1452d1bae 100644
--- a/test/res.sendFile.js
+++ b/test/res.sendFile.js
@@ -1,120 +1,120 @@
 'use strict'
 
-var after = require('after');
-var assert = require('node:assert')
-var AsyncLocalStorage = require('node:async_hooks').AsyncLocalStorage
-const { Buffer } = require('node:buffer');
-
-var express = require('../')
-  , request = require('supertest')
-var onFinished = require('on-finished');
-var path = require('node:path');
-var fixtures = path.join(__dirname, 'fixtures');
-var utils = require('./support/utils');
-
-describe('res', function(){
-  describe('.sendFile(path)', function () {
-    it('should error missing path', function (done) {
-      var app = createApp();
+const after = require('after')
+const assert = require('node:assert')
+const { AsyncLocalStorage } = require('node:async_hooks')
+const { Buffer } = require('node:buffer')
+
+const express = require('../')
+const request = require('supertest')
+const onFinished = require('on-finished')
+const path = require('node:path')
+const fixtures = path.join(__dirname, 'fixtures')
+const utils = require('./support/utils')
+
+describe('res', () => {
+  describe('.sendFile(path)', () => {
+    it('should error missing path', (done) => {
+      const app = createApp()
 
       request(app)
-      .get('/')
-      .expect(500, /path.*required/, done);
-    });
+        .get('/')
+        .expect(500, /path.*required/, done)
+    })
 
-    it('should error for non-string path', function (done) {
-      var app = createApp(42)
+    it('should error for non-string path', (done) => {
+      const app = createApp(42)
 
       request(app)
-      .get('/')
-      .expect(500, /TypeError: path must be a string to res.sendFile/, done)
+        .get('/')
+        .expect(500, /TypeError: path must be a string to res.sendFile/, done)
     })
 
-    it('should error for non-absolute path', function (done) {
-      var app = createApp('name.txt')
+    it('should error for non-absolute path', (done) => {
+      const app = createApp('name.txt')
 
       request(app)
         .get('/')
         .expect(500, /TypeError: path must be absolute/, done)
     })
 
-    it('should transfer a file', function (done) {
-      var app = createApp(path.resolve(fixtures, 'name.txt'));
+    it('should transfer a file', (done) => {
+      const app = createApp(path.resolve(fixtures, 'name.txt'))
 
       request(app)
-      .get('/')
-      .expect(200, 'tobi', done);
-    });
+        .get('/')
+        .expect(200, 'tobi', done)
+    })
 
-    it('should transfer a file with special characters in string', function (done) {
-      var app = createApp(path.resolve(fixtures, '% of dogs.txt'));
+    it('should transfer a file with special characters in string', (done) => {
+      const app = createApp(path.resolve(fixtures, '% of dogs.txt'))
 
       request(app)
-      .get('/')
-      .expect(200, '20%', done);
-    });
+        .get('/')
+        .expect(200, '20%', done)
+    })
 
-    it('should include ETag', function (done) {
-      var app = createApp(path.resolve(fixtures, 'name.txt'));
+    it('should include ETag', (done) => {
+      const app = createApp(path.resolve(fixtures, 'name.txt'))
 
       request(app)
-      .get('/')
-      .expect('ETag', /^(?:W\/)?"[^"]+"$/)
-      .expect(200, 'tobi', done);
-    });
+        .get('/')
+        .expect('ETag', /^(?:W\/)?"[^"]+"$/)
+        .expect(200, 'tobi', done)
+    })
 
-    it('should 304 when ETag matches', function (done) {
-      var app = createApp(path.resolve(fixtures, 'name.txt'));
+    it('should 304 when ETag matches', (done) => {
+      const app = createApp(path.resolve(fixtures, 'name.txt'))
 
       request(app)
-      .get('/')
-      .expect('ETag', /^(?:W\/)?"[^"]+"$/)
-      .expect(200, 'tobi', function (err, res) {
-        if (err) return done(err);
-        var etag = res.headers.etag;
-        request(app)
         .get('/')
-        .set('If-None-Match', etag)
-        .expect(304, done);
-      });
-    });
+        .expect('ETag', /^(?:W\/)?"[^"]+"$/)
+        .expect(200, 'tobi', (err, res) => {
+          if (err) return done(err)
+          const etag = res.headers.etag
+          request(app)
+            .get('/')
+            .set('If-None-Match', etag)
+            .expect(304, done)
+        })
+    })
 
-    it('should disable the ETag function if requested', function (done) {
-      var app = createApp(path.resolve(fixtures, 'name.txt')).disable('etag');
+    it('should disable the ETag function if requested', (done) => {
+      const app = createApp(path.resolve(fixtures, 'name.txt')).disable('etag')
 
       request(app)
-      .get('/')
-      .expect(handleHeaders)
-      .expect(200, done);
+        .get('/')
+        .expect(handleHeaders)
+        .expect(200, done)
 
       function handleHeaders (res) {
-        assert(res.headers.etag === undefined);
+        assert(res.headers.etag === undefined)
       }
-    });
+    })
 
-    it('should 404 for directory', function (done) {
-      var app = createApp(path.resolve(fixtures, 'blog'));
+    it('should 404 for directory', (done) => {
+      const app = createApp(path.resolve(fixtures, 'blog'))
 
       request(app)
-      .get('/')
-      .expect(404, done);
-    });
+        .get('/')
+        .expect(404, done)
+    })
 
-    it('should 404 when not found', function (done) {
-      var app = createApp(path.resolve(fixtures, 'does-no-exist'));
+    it('should 404 when not found', (done) => {
+      const app = createApp(path.resolve(fixtures, 'does-no-exist'))
 
-      app.use(function (req, res) {
-        res.statusCode = 200;
-        res.send('no!');
-      });
+      app.use((req, res) => {
+        res.statusCode = 200
+        res.send('no!')
+      })
 
       request(app)
-      .get('/')
-      .expect(404, done);
-    });
+        .get('/')
+        .expect(404, done)
+    })
 
-    it('should send cache-control by default', function (done) {
-      var app = createApp(path.resolve(__dirname, 'fixtures/name.txt'))
+    it('should send cache-control by default', (done) => {
+      const app = createApp(path.resolve(__dirname, 'fixtures/name.txt'))
 
       request(app)
         .get('/')
@@ -122,177 +122,177 @@ describe('res', function(){
         .expect(200, done)
     })
 
-    it('should not serve dotfiles by default', function (done) {
-      var app = createApp(path.resolve(__dirname, 'fixtures/.name'))
+    it('should not serve dotfiles by default', (done) => {
+      const app = createApp(path.resolve(__dirname, 'fixtures/.name'))
 
       request(app)
         .get('/')
         .expect(404, done)
     })
 
-    it('should not override manual content-types', function (done) {
-      var app = express();
+    it('should not override manual content-types', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.contentType('application/x-bogus');
-        res.sendFile(path.resolve(fixtures, 'name.txt'));
-      });
+      app.use((req, res) => {
+        res.contentType('application/x-bogus')
+        res.sendFile(path.resolve(fixtures, 'name.txt'))
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'application/x-bogus')
-      .end(done);
+        .get('/')
+        .expect('Content-Type', 'application/x-bogus')
+        .end(done)
     })
 
-    it('should not error if the client aborts', function (done) {
-      var app = express();
-      var cb = after(2, done)
-      var error = null
+    it('should not error if the client aborts', (done) => {
+      const app = express()
+      const cb = after(2, done)
+      let error = null
 
-      app.use(function (req, res) {
-        setImmediate(function () {
-          res.sendFile(path.resolve(fixtures, 'name.txt'));
-          setTimeout(function () {
+      app.use((req, res) => {
+        setImmediate(() => {
+          res.sendFile(path.resolve(fixtures, 'name.txt'))
+          setTimeout(() => {
             cb(error)
           }, 10)
         })
         test.req.abort()
-      });
+      })
 
-      app.use(function (err, req, res, next) {
+      app.use((err, req, res, next) => {
         error = err
         next(err)
-      });
+      })
 
-      var server = app.listen()
-      var test = request(server).get('/')
-      test.end(function (err) {
+      const server = app.listen()
+      const test = request(server).get('/')
+      test.end((err) => {
         assert.ok(err)
         server.close(cb)
       })
     })
   })
 
-  describe('.sendFile(path, fn)', function () {
-    it('should invoke the callback when complete', function (done) {
-      var cb = after(2, done);
-      var app = createApp(path.resolve(fixtures, 'name.txt'), cb);
+  describe('.sendFile(path, fn)', () => {
+    it('should invoke the callback when complete', (done) => {
+      const cb = after(2, done)
+      const app = createApp(path.resolve(fixtures, 'name.txt'), cb)
 
       request(app)
-      .get('/')
-      .expect(200, cb);
+        .get('/')
+        .expect(200, cb)
     })
 
-    it('should invoke the callback when client aborts', function (done) {
-      var cb = after(2, done)
-      var app = express();
+    it('should invoke the callback when client aborts', (done) => {
+      const cb = after(2, done)
+      const app = express()
 
-      app.use(function (req, res) {
-        setImmediate(function () {
-          res.sendFile(path.resolve(fixtures, 'name.txt'), function (err) {
+      app.use((req, res) => {
+        setImmediate(() => {
+          res.sendFile(path.resolve(fixtures, 'name.txt'), (err) => {
             assert.ok(err)
             assert.strictEqual(err.code, 'ECONNABORTED')
             cb()
-          });
-        });
+          })
+        })
         test.req.abort()
-      });
+      })
 
-      var server = app.listen()
-      var test = request(server).get('/')
-      test.end(function (err) {
+      const server = app.listen()
+      const test = request(server).get('/')
+      test.end((err) => {
         assert.ok(err)
         server.close(cb)
       })
     })
 
-    it('should invoke the callback when client already aborted', function (done) {
-      var cb = after(2, done)
-      var app = express();
+    it('should invoke the callback when client already aborted', (done) => {
+      const cb = after(2, done)
+      const app = express()
 
-      app.use(function (req, res) {
-        onFinished(res, function () {
-          res.sendFile(path.resolve(fixtures, 'name.txt'), function (err) {
+      app.use((req, res) => {
+        onFinished(res, () => {
+          res.sendFile(path.resolve(fixtures, 'name.txt'), (err) => {
             assert.ok(err)
             assert.strictEqual(err.code, 'ECONNABORTED')
             cb()
-          });
-        });
+          })
+        })
         test.req.abort()
-      });
+      })
 
-      var server = app.listen()
-      var test = request(server).get('/')
-      test.end(function (err) {
+      const server = app.listen()
+      const test = request(server).get('/')
+      test.end((err) => {
         assert.ok(err)
         server.close(cb)
       })
     })
 
-    it('should invoke the callback without error when HEAD', function (done) {
-      var app = express();
-      var cb = after(2, done);
+    it('should invoke the callback without error when HEAD', (done) => {
+      const app = express()
+      const cb = after(2, done)
 
-      app.use(function (req, res) {
-        res.sendFile(path.resolve(fixtures, 'name.txt'), cb);
-      });
+      app.use((req, res) => {
+        res.sendFile(path.resolve(fixtures, 'name.txt'), cb)
+      })
 
       request(app)
-      .head('/')
-      .expect(200, cb);
-    });
+        .head('/')
+        .expect(200, cb)
+    })
 
-    it('should invoke the callback without error when 304', function (done) {
-      var app = express();
-      var cb = after(3, done);
+    it('should invoke the callback without error when 304', (done) => {
+      const app = express()
+      const cb = after(3, done)
 
-      app.use(function (req, res) {
-        res.sendFile(path.resolve(fixtures, 'name.txt'), cb);
-      });
+      app.use((req, res) => {
+        res.sendFile(path.resolve(fixtures, 'name.txt'), cb)
+      })
 
       request(app)
-      .get('/')
-      .expect('ETag', /^(?:W\/)?"[^"]+"$/)
-      .expect(200, 'tobi', function (err, res) {
-        if (err) return cb(err);
-        var etag = res.headers.etag;
-        request(app)
         .get('/')
-        .set('If-None-Match', etag)
-        .expect(304, cb);
-      });
-    });
+        .expect('ETag', /^(?:W\/)?"[^"]+"$/)
+        .expect(200, 'tobi', (err, res) => {
+          if (err) return cb(err)
+          const etag = res.headers.etag
+          request(app)
+            .get('/')
+            .set('If-None-Match', etag)
+            .expect(304, cb)
+        })
+    })
 
-    it('should invoke the callback on 404', function(done){
-      var app = express();
+    it('should invoke the callback on 404', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.sendFile(path.resolve(fixtures, 'does-not-exist'), function (err) {
+      app.use((req, res) => {
+        res.sendFile(path.resolve(fixtures, 'does-not-exist'), (err) => {
           res.send(err ? 'got ' + err.status + ' error' : 'no error')
-        });
-      });
+        })
+      })
 
       request(app)
         .get('/')
         .expect(200, 'got 404 error', done)
     })
 
-    describe('async local storage', function () {
-      it('should persist store', function (done) {
-        var app = express()
-        var cb = after(2, done)
-        var store = { foo: 'bar' }
+    describe('async local storage', () => {
+      it('should persist store', (done) => {
+        const app = express()
+        const cb = after(2, done)
+        const store = { foo: 'bar' }
 
-        app.use(function (req, res, next) {
+        app.use((req, res, next) => {
           req.asyncLocalStorage = new AsyncLocalStorage()
           req.asyncLocalStorage.run(store, next)
         })
 
-        app.use(function (req, res) {
-          res.sendFile(path.resolve(fixtures, 'name.txt'), function (err) {
+        app.use((req, res) => {
+          res.sendFile(path.resolve(fixtures, 'name.txt'), (err) => {
             if (err) return cb(err)
 
-            var local = req.asyncLocalStorage.getStore()
+            const local = req.asyncLocalStorage.getStore()
 
             assert.strictEqual(local.foo, 'bar')
             cb()
@@ -305,18 +305,18 @@ describe('res', function(){
           .expect(200, 'tobi', cb)
       })
 
-      it('should persist store on error', function (done) {
-        var app = express()
-        var store = { foo: 'bar' }
+      it('should persist store on error', (done) => {
+        const app = express()
+        const store = { foo: 'bar' }
 
-        app.use(function (req, res, next) {
+        app.use((req, res, next) => {
           req.asyncLocalStorage = new AsyncLocalStorage()
           req.asyncLocalStorage.run(store, next)
         })
 
-        app.use(function (req, res) {
-          res.sendFile(path.resolve(fixtures, 'does-not-exist'), function (err) {
-            var local = req.asyncLocalStorage.getStore()
+        app.use((req, res) => {
+          res.sendFile(path.resolve(fixtures, 'does-not-exist'), (err) => {
+            const local = req.asyncLocalStorage.getStore()
 
             if (local) {
               res.setHeader('x-store-foo', String(local.foo))
@@ -336,19 +336,19 @@ describe('res', function(){
     })
   })
 
-  describe('.sendFile(path, options)', function () {
-    it('should pass options to send module', function (done) {
+  describe('.sendFile(path, options)', () => {
+    it('should pass options to send module', (done) => {
       request(createApp(path.resolve(fixtures, 'name.txt'), { start: 0, end: 1 }))
-      .get('/')
-      .expect(200, 'to', done)
+        .get('/')
+        .expect(200, 'to', done)
     })
 
-    describe('with "acceptRanges" option', function () {
-      describe('when true', function () {
-        it('should advertise byte range accepted', function (done) {
-          var app = express()
+    describe('with "acceptRanges" option', () => {
+      describe('when true', () => {
+        it('should advertise byte range accepted', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'nums.txt'), {
               acceptRanges: true
             })
@@ -362,10 +362,10 @@ describe('res', function(){
             .end(done)
         })
 
-        it('should respond to range request', function (done) {
-          var app = express()
+        it('should respond to range request', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'nums.txt'), {
               acceptRanges: true
             })
@@ -378,11 +378,11 @@ describe('res', function(){
         })
       })
 
-      describe('when false', function () {
-        it('should not advertise accept-ranges', function (done) {
-          var app = express()
+      describe('when false', () => {
+        it('should not advertise accept-ranges', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'nums.txt'), {
               acceptRanges: false
             })
@@ -395,10 +395,10 @@ describe('res', function(){
             .end(done)
         })
 
-        it('should not honor range requests', function (done) {
-          var app = express()
+        it('should not honor range requests', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'nums.txt'), {
               acceptRanges: false
             })
@@ -412,12 +412,12 @@ describe('res', function(){
       })
     })
 
-    describe('with "cacheControl" option', function () {
-      describe('when true', function () {
-        it('should send cache-control header', function (done) {
-          var app = express()
+    describe('with "cacheControl" option', () => {
+      describe('when true', () => {
+        it('should send cache-control header', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               cacheControl: true
             })
@@ -431,11 +431,11 @@ describe('res', function(){
         })
       })
 
-      describe('when false', function () {
-        it('should not send cache-control header', function (done) {
-          var app = express()
+      describe('when false', () => {
+        it('should not send cache-control header', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               cacheControl: false
             })
@@ -450,12 +450,12 @@ describe('res', function(){
       })
     })
 
-    describe('with "dotfiles" option', function () {
-      describe('when "allow"', function () {
-        it('should allow dotfiles', function (done) {
-          var app = express()
+    describe('with "dotfiles" option', () => {
+      describe('when "allow"', () => {
+        it('should allow dotfiles', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, '.name'), {
               dotfiles: 'allow'
             })
@@ -469,11 +469,11 @@ describe('res', function(){
         })
       })
 
-      describe('when "deny"', function () {
-        it('should deny dotfiles', function (done) {
-          var app = express()
+      describe('when "deny"', () => {
+        it('should deny dotfiles', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, '.name'), {
               dotfiles: 'deny'
             })
@@ -487,11 +487,11 @@ describe('res', function(){
         })
       })
 
-      describe('when "ignore"', function () {
-        it('should ignore dotfiles', function (done) {
-          var app = express()
+      describe('when "ignore"', () => {
+        it('should ignore dotfiles', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, '.name'), {
               dotfiles: 'ignore'
             })
@@ -506,11 +506,11 @@ describe('res', function(){
       })
     })
 
-    describe('with "headers" option', function () {
-      it('should set headers on response', function (done) {
-        var app = express()
+    describe('with "headers" option', () => {
+      it('should set headers on response', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile(path.resolve(fixtures, 'user.html'), {
             headers: {
               'X-Foo': 'Bar',
@@ -527,10 +527,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should use last header when duplicated', function (done) {
-        var app = express()
+      it('should use last header when duplicated', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile(path.resolve(fixtures, 'user.html'), {
             headers: {
               'X-Foo': 'Bar',
@@ -546,10 +546,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should override Content-Type', function (done) {
-        var app = express()
+      it('should override Content-Type', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile(path.resolve(fixtures, 'user.html'), {
             headers: {
               'Content-Type': 'text/x-custom'
@@ -564,10 +564,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should not set headers on 404', function (done) {
-        var app = express()
+      it('should not set headers on 404', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile(path.resolve(fixtures, 'does-not-exist'), {
             headers: {
               'X-Foo': 'Bar'
@@ -583,12 +583,12 @@ describe('res', function(){
       })
     })
 
-    describe('with "immutable" option', function () {
-      describe('when true', function () {
-        it('should send cache-control header with immutable', function (done) {
-          var app = express()
+    describe('with "immutable" option', () => {
+      describe('when true', () => {
+        it('should send cache-control header with immutable', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               immutable: true
             })
@@ -602,11 +602,11 @@ describe('res', function(){
         })
       })
 
-      describe('when false', function () {
-        it('should not send cache-control header with immutable', function (done) {
-          var app = express()
+      describe('when false', () => {
+        it('should not send cache-control header with immutable', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               immutable: false
             })
@@ -621,12 +621,12 @@ describe('res', function(){
       })
     })
 
-    describe('with "lastModified" option', function () {
-      describe('when true', function () {
-        it('should send last-modified header', function (done) {
-          var app = express()
+    describe('with "lastModified" option', () => {
+      describe('when true', () => {
+        it('should send last-modified header', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               lastModified: true
             })
@@ -639,10 +639,10 @@ describe('res', function(){
             .end(done)
         })
 
-        it('should conditionally respond with if-modified-since', function (done) {
-          var app = express()
+        it('should conditionally respond with if-modified-since', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               lastModified: true
             })
@@ -655,11 +655,11 @@ describe('res', function(){
         })
       })
 
-      describe('when false', function () {
-        it('should not have last-modified header', function (done) {
-          var app = express()
+      describe('when false', () => {
+        it('should not have last-modified header', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               lastModified: false
             })
@@ -672,10 +672,10 @@ describe('res', function(){
             .end(done)
         })
 
-        it('should not honor if-modified-since', function (done) {
-          var app = express()
+        it('should not honor if-modified-since', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               lastModified: false
             })
@@ -691,11 +691,11 @@ describe('res', function(){
       })
     })
 
-    describe('with "maxAge" option', function () {
-      it('should set cache-control max-age to milliseconds', function (done) {
-        var app = express()
+    describe('with "maxAge" option', () => {
+      it('should set cache-control max-age to milliseconds', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile(path.resolve(fixtures, 'user.html'), {
             maxAge: 20000
           })
@@ -708,10 +708,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should cap cache-control max-age to 1 year', function (done) {
-        var app = express()
+      it('should cap cache-control max-age to 1 year', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile(path.resolve(fixtures, 'user.html'), {
             maxAge: 99999999999
           })
@@ -724,10 +724,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should min cache-control max-age to 0', function (done) {
-        var app = express()
+      it('should min cache-control max-age to 0', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile(path.resolve(fixtures, 'user.html'), {
             maxAge: -20000
           })
@@ -740,10 +740,10 @@ describe('res', function(){
           .end(done)
       })
 
-      it('should floor cache-control max-age', function (done) {
-        var app = express()
+      it('should floor cache-control max-age', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile(path.resolve(fixtures, 'user.html'), {
             maxAge: 21911.23
           })
@@ -756,11 +756,11 @@ describe('res', function(){
           .end(done)
       })
 
-      describe('when cacheControl: false', function () {
-        it('should not send cache-control', function (done) {
-          var app = express()
+      describe('when cacheControl: false', () => {
+        it('should not send cache-control', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               cacheControl: false,
               maxAge: 20000
@@ -775,11 +775,11 @@ describe('res', function(){
         })
       })
 
-      describe('when string', function () {
-        it('should accept plain number as milliseconds', function (done) {
-          var app = express()
+      describe('when string', () => {
+        it('should accept plain number as milliseconds', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               maxAge: '20000'
             })
@@ -792,10 +792,10 @@ describe('res', function(){
             .end(done)
         })
 
-        it('should accept suffix "s" for seconds', function (done) {
-          var app = express()
+        it('should accept suffix "s" for seconds', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               maxAge: '20s'
             })
@@ -808,10 +808,10 @@ describe('res', function(){
             .end(done)
         })
 
-        it('should accept suffix "m" for minutes', function (done) {
-          var app = express()
+        it('should accept suffix "m" for minutes', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               maxAge: '20m'
             })
@@ -824,10 +824,10 @@ describe('res', function(){
             .end(done)
         })
 
-        it('should accept suffix "d" for days', function (done) {
-          var app = express()
+        it('should accept suffix "d" for days', (done) => {
+          const app = express()
 
-          app.use(function (req, res) {
+          app.use((req, res) => {
             res.sendFile(path.resolve(fixtures, 'user.html'), {
               maxAge: '20d'
             })
@@ -842,11 +842,11 @@ describe('res', function(){
       })
     })
 
-    describe('with "root" option', function () {
-      it('should allow relative path', function (done) {
-        var app = express()
+    describe('with "root" option', () => {
+      it('should allow relative path', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile('name.txt', {
             root: fixtures
           })
@@ -857,10 +857,10 @@ describe('res', function(){
           .expect(200, 'tobi', done)
       })
 
-      it('should allow up within root', function (done) {
-        var app = express()
+      it('should allow up within root', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile('fake/../name.txt', {
             root: fixtures
           })
@@ -871,10 +871,10 @@ describe('res', function(){
           .expect(200, 'tobi', done)
       })
 
-      it('should reject up outside root', function (done) {
-        var app = express()
+      it('should reject up outside root', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile('..' + path.sep + path.relative(path.dirname(fixtures), path.join(fixtures, 'name.txt')), {
             root: fixtures
           })
@@ -885,10 +885,10 @@ describe('res', function(){
           .expect(403, done)
       })
 
-      it('should reject reading outside root', function (done) {
-        var app = express()
+      it('should reject reading outside root', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.sendFile('../name.txt', {
             root: fixtures
           })
@@ -902,12 +902,12 @@ describe('res', function(){
   })
 })
 
-function createApp(path, options, fn) {
-  var app = express();
+function createApp (path, options, fn) {
+  const app = express()
 
-  app.use(function (req, res) {
-    res.sendFile(path, options, fn);
-  });
+  app.use((req, res) => {
+    res.sendFile(path, options, fn)
+  })
 
-  return app;
+  return app
 }
diff --git a/test/res.sendStatus.js b/test/res.sendStatus.js
index b244cf9d173..56b2f22e983 100644
--- a/test/res.sendStatus.js
+++ b/test/res.sendStatus.js
@@ -1,38 +1,38 @@
 'use strict'
 
-var express = require('..')
-var request = require('supertest')
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function () {
-  describe('.sendStatus(statusCode)', function () {
-    it('should send the status code and message as body', function (done) {
-      var app = express();
+describe('res', () => {
+  describe('.sendStatus(statusCode)', () => {
+    it('should send the status code and message as body', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.sendStatus(201);
-      });
+      app.use((req, res) => {
+        res.sendStatus(201)
+      })
 
       request(app)
-      .get('/')
-      .expect(201, 'Created', done);
+        .get('/')
+        .expect(201, 'Created', done)
     })
 
-    it('should work with unknown code', function (done) {
-      var app = express();
+    it('should work with unknown code', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.sendStatus(599);
-      });
+      app.use((req, res) => {
+        res.sendStatus(599)
+      })
 
       request(app)
-      .get('/')
-      .expect(599, '599', done);
+        .get('/')
+        .expect(599, '599', done)
     })
 
-    it('should raise error for invalid status code', function (done) {
-      var app = express()
+    it('should raise error for invalid status code', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.sendStatus(undefined).end()
       })
 
diff --git a/test/res.set.js b/test/res.set.js
index 04511c1c95f..6bacdc8644c 100644
--- a/test/res.set.js
+++ b/test/res.set.js
@@ -1,124 +1,124 @@
 'use strict'
 
-var express = require('..');
-var request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function(){
-  describe('.set(field, value)', function(){
-    it('should set the response header field', function(done){
-      var app = express();
+describe('res', () => {
+  describe('.set(field, value)', () => {
+    it('should set the response header field', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.set('Content-Type', 'text/x-foo; charset=utf-8').end();
-      });
+      app.use((req, res) => {
+        res.set('Content-Type', 'text/x-foo; charset=utf-8').end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/x-foo; charset=utf-8')
-      .end(done);
+        .get('/')
+        .expect('Content-Type', 'text/x-foo; charset=utf-8')
+        .end(done)
     })
 
-    it('should coerce to a string', function (done) {
-      var app = express();
+    it('should coerce to a string', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.set('X-Number', 123);
-        res.end(typeof res.get('X-Number'));
-      });
+      app.use((req, res) => {
+        res.set('X-Number', 123)
+        res.end(typeof res.get('X-Number'))
+      })
 
       request(app)
-      .get('/')
-      .expect('X-Number', '123')
-      .expect(200, 'string', done);
+        .get('/')
+        .expect('X-Number', '123')
+        .expect(200, 'string', done)
     })
   })
 
-  describe('.set(field, values)', function(){
-    it('should set multiple response header fields', function(done){
-      var app = express();
+  describe('.set(field, values)', () => {
+    it('should set multiple response header fields', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.set('Set-Cookie', ["type=ninja", "language=javascript"]);
-        res.send(res.get('Set-Cookie'));
-      });
+      app.use((req, res) => {
+        res.set('Set-Cookie', ['type=ninja', 'language=javascript'])
+        res.send(res.get('Set-Cookie'))
+      })
 
       request(app)
-      .get('/')
-      .expect('["type=ninja","language=javascript"]', done);
+        .get('/')
+        .expect('["type=ninja","language=javascript"]', done)
     })
 
-    it('should coerce to an array of strings', function (done) {
-      var app = express();
+    it('should coerce to an array of strings', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.set('X-Numbers', [123, 456]);
-        res.end(JSON.stringify(res.get('X-Numbers')));
-      });
+      app.use((req, res) => {
+        res.set('X-Numbers', [123, 456])
+        res.end(JSON.stringify(res.get('X-Numbers')))
+      })
 
       request(app)
-      .get('/')
-      .expect('X-Numbers', '123, 456')
-      .expect(200, '["123","456"]', done);
+        .get('/')
+        .expect('X-Numbers', '123, 456')
+        .expect(200, '["123","456"]', done)
     })
 
-    it('should not set a charset of one is already set', function (done) {
-      var app = express();
+    it('should not set a charset of one is already set', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.set('Content-Type', 'text/html; charset=lol');
-        res.end();
-      });
+      app.use((req, res) => {
+        res.set('Content-Type', 'text/html; charset=lol')
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/html; charset=lol')
-      .expect(200, done);
+        .get('/')
+        .expect('Content-Type', 'text/html; charset=lol')
+        .expect(200, done)
     })
 
-    it('should throw when Content-Type is an array', function (done) {
-      var app = express()
+    it('should throw when Content-Type is an array', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
+      app.use((req, res) => {
         res.set('Content-Type', ['text/html'])
         res.end()
-      });
+      })
 
       request(app)
-      .get('/')
-      .expect(500, /TypeError: Content-Type cannot be set to an Array/, done)
+        .get('/')
+        .expect(500, /TypeError: Content-Type cannot be set to an Array/, done)
     })
   })
 
-  describe('.set(object)', function(){
-    it('should set multiple fields', function(done){
-      var app = express();
+  describe('.set(object)', () => {
+    it('should set multiple fields', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.set({
           'X-Foo': 'bar',
           'X-Bar': 'baz'
-        }).end();
-      });
+        }).end()
+      })
 
       request(app)
-      .get('/')
-      .expect('X-Foo', 'bar')
-      .expect('X-Bar', 'baz')
-      .end(done);
+        .get('/')
+        .expect('X-Foo', 'bar')
+        .expect('X-Bar', 'baz')
+        .end(done)
     })
 
-    it('should coerce to a string', function (done) {
-      var app = express();
+    it('should coerce to a string', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.set({ 'X-Number': 123 });
-        res.end(typeof res.get('X-Number'));
-      });
+      app.use((req, res) => {
+        res.set({ 'X-Number': 123 })
+        res.end(typeof res.get('X-Number'))
+      })
 
       request(app)
-      .get('/')
-      .expect('X-Number', '123')
-      .expect(200, 'string', done);
+        .get('/')
+        .expect('X-Number', '123')
+        .expect(200, 'string', done)
     })
   })
 })
diff --git a/test/res.status.js b/test/res.status.js
index 59c8a57e702..421c388594c 100644
--- a/test/res.status.js
+++ b/test/res.status.js
@@ -1,28 +1,27 @@
 'use strict'
-const express = require('../.');
-const request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function () {
-  describe('.status(code)', function () {
+describe('res', () => {
+  describe('.status(code)', () => {
+    it('should set the status code when valid', (done) => {
+      const app = express()
 
-    it('should set the status code when valid', function (done) {
-      var app = express();
-
-      app.use(function (req, res) {
-        res.status(200).end();
-      });
+      app.use((req, res) => {
+        res.status(200).end()
+      })
 
       request(app)
         .get('/')
-        .expect(200, done);
-    });
+        .expect(200, done)
+    })
 
-    describe('accept valid ranges', function() {
+    describe('accept valid ranges', () => {
       // not testing w/ 100, because that has specific meaning and behavior in Node as Expect: 100-continue
-      it('should set the response status code to 101', function (done) {
-        var app = express()
+      it('should set the response status code to 101', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.status(101).end()
         })
 
@@ -31,10 +30,10 @@ describe('res', function () {
           .expect(101, done)
       })
 
-      it('should set the response status code to 201', function (done) {
-        var app = express()
+      it('should set the response status code to 201', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.status(201).end()
         })
 
@@ -43,10 +42,10 @@ describe('res', function () {
           .expect(201, done)
       })
 
-      it('should set the response status code to 302', function (done) {
-        var app = express()
+      it('should set the response status code to 302', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.status(302).end()
         })
 
@@ -55,10 +54,10 @@ describe('res', function () {
           .expect(302, done)
       })
 
-      it('should set the response status code to 403', function (done) {
-        var app = express()
+      it('should set the response status code to 403', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.status(403).end()
         })
 
@@ -67,10 +66,10 @@ describe('res', function () {
           .expect(403, done)
       })
 
-      it('should set the response status code to 501', function (done) {
-        var app = express()
+      it('should set the response status code to 501', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.status(501).end()
         })
 
@@ -79,10 +78,10 @@ describe('res', function () {
           .expect(501, done)
       })
 
-      it('should set the response status code to 700', function (done) {
-        var app = express()
+      it('should set the response status code to 700', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.status(700).end()
         })
 
@@ -91,10 +90,10 @@ describe('res', function () {
           .expect(700, done)
       })
 
-      it('should set the response status code to 800', function (done) {
-        var app = express()
+      it('should set the response status code to 800', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.status(800).end()
         })
 
@@ -103,10 +102,10 @@ describe('res', function () {
           .expect(800, done)
       })
 
-      it('should set the response status code to 900', function (done) {
-        var app = express()
+      it('should set the response status code to 900', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
+        app.use((req, res) => {
           res.status(900).end()
         })
 
@@ -116,91 +115,90 @@ describe('res', function () {
       })
     })
 
-    describe('invalid status codes', function () {
-      it('should raise error for status code below 100', function (done) {
-        var app = express();
+    describe('invalid status codes', () => {
+      it('should raise error for status code below 100', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.status(99).end();
-        });
+        app.use((req, res) => {
+          res.status(99).end()
+        })
 
         request(app)
           .get('/')
-          .expect(500, /Invalid status code/, done);
-      });
+          .expect(500, /Invalid status code/, done)
+      })
 
-      it('should raise error for status code above 999', function (done) {
-        var app = express();
+      it('should raise error for status code above 999', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.status(1000).end();
-        });
+        app.use((req, res) => {
+          res.status(1000).end()
+        })
 
         request(app)
           .get('/')
-          .expect(500, /Invalid status code/, done);
-      });
+          .expect(500, /Invalid status code/, done)
+      })
 
-      it('should raise error for non-integer status codes', function (done) {
-        var app = express();
+      it('should raise error for non-integer status codes', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.status(200.1).end();
-        });
+        app.use((req, res) => {
+          res.status(200.1).end()
+        })
 
         request(app)
           .get('/')
-          .expect(500, /Invalid status code/, done);
-      });
+          .expect(500, /Invalid status code/, done)
+      })
 
-      it('should raise error for undefined status code', function (done) {
-        var app = express();
+      it('should raise error for undefined status code', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.status(undefined).end();
-        });
+        app.use((req, res) => {
+          res.status(undefined).end()
+        })
 
         request(app)
           .get('/')
-          .expect(500, /Invalid status code/, done);
-      });
+          .expect(500, /Invalid status code/, done)
+      })
 
-      it('should raise error for null status code', function (done) {
-        var app = express();
+      it('should raise error for null status code', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.status(null).end();
-        });
+        app.use((req, res) => {
+          res.status(null).end()
+        })
 
         request(app)
           .get('/')
-          .expect(500, /Invalid status code/, done);
-      });
+          .expect(500, /Invalid status code/, done)
+      })
 
-      it('should raise error for string status code', function (done) {
-        var app = express();
+      it('should raise error for string status code', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.status("200").end();
-        });
+        app.use((req, res) => {
+          res.status('200').end()
+        })
 
         request(app)
           .get('/')
-          .expect(500, /Invalid status code/, done);
-      });
+          .expect(500, /Invalid status code/, done)
+      })
 
-      it('should raise error for NaN status code', function (done) {
-        var app = express();
+      it('should raise error for NaN status code', (done) => {
+        const app = express()
 
-        app.use(function (req, res) {
-          res.status(NaN).end();
-        });
+        app.use((req, res) => {
+          res.status(NaN).end()
+        })
 
         request(app)
           .get('/')
-          .expect(500, /Invalid status code/, done);
-      });
-    });
-  });
-});
-
+          .expect(500, /Invalid status code/, done)
+      })
+    })
+  })
+})
diff --git a/test/res.type.js b/test/res.type.js
index 09285af3914..98d0cb3a780 100644
--- a/test/res.type.js
+++ b/test/res.type.js
@@ -1,46 +1,46 @@
 'use strict'
 
-var express = require('../')
-  , request = require('supertest');
+const express = require('../')
+const request = require('supertest')
 
-describe('res', function(){
-  describe('.type(str)', function(){
-    it('should set the Content-Type based on a filename', function(done){
-      var app = express();
+describe('res', () => {
+  describe('.type(str)', () => {
+    it('should set the Content-Type based on a filename', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.type('foo.js').end('var name = "tj";');
-      });
+      app.use((req, res) => {
+        res.type('foo.js').end('var name = "tj";')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'text/javascript; charset=utf-8')
-      .end(done)
+        .get('/')
+        .expect('Content-Type', 'text/javascript; charset=utf-8')
+        .end(done)
     })
 
-    it('should default to application/octet-stream', function(done){
-      var app = express();
+    it('should default to application/octet-stream', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
-        res.type('rawr').end('var name = "tj";');
-      });
+      app.use((req, res) => {
+        res.type('rawr').end('var name = "tj";')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'application/octet-stream', done);
+        .get('/')
+        .expect('Content-Type', 'application/octet-stream', done)
     })
 
-    it('should set the Content-Type with type/subtype', function(done){
-      var app = express();
+    it('should set the Content-Type with type/subtype', (done) => {
+      const app = express()
 
-      app.use(function(req, res){
+      app.use((req, res) => {
         res.type('application/vnd.amazon.ebook')
-          .end('var name = "tj";');
-      });
+          .end('var name = "tj";')
+      })
 
       request(app)
-      .get('/')
-      .expect('Content-Type', 'application/vnd.amazon.ebook', done);
+        .get('/')
+        .expect('Content-Type', 'application/vnd.amazon.ebook', done)
     })
   })
 })
diff --git a/test/res.vary.js b/test/res.vary.js
index ff3c9716529..9aab950461c 100644
--- a/test/res.vary.js
+++ b/test/res.vary.js
@@ -1,90 +1,90 @@
 'use strict'
 
-var express = require('..');
-var request = require('supertest');
-var utils = require('./support/utils');
+const express = require('../')
+const request = require('supertest')
+const utils = require('./support/utils')
 
-describe('res.vary()', function(){
-  describe('with no arguments', function(){
-    it('should throw error', function (done) {
-      var app = express();
+describe('res.vary()', () => {
+  describe('with no arguments', () => {
+    it('should throw error', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.vary();
-        res.end();
-      });
+      app.use((req, res) => {
+        res.vary()
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect(500, /field.*required/, done)
+        .get('/')
+        .expect(500, /field.*required/, done)
     })
   })
 
-  describe('with an empty array', function(){
-    it('should not set Vary', function (done) {
-      var app = express();
+  describe('with an empty array', () => {
+    it('should not set Vary', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.vary([]);
-        res.end();
-      });
+      app.use((req, res) => {
+        res.vary([])
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect(utils.shouldNotHaveHeader('Vary'))
-      .expect(200, done);
+        .get('/')
+        .expect(utils.shouldNotHaveHeader('Vary'))
+        .expect(200, done)
     })
   })
 
-  describe('with an array', function(){
-    it('should set the values', function (done) {
-      var app = express();
+  describe('with an array', () => {
+    it('should set the values', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.vary(['Accept', 'Accept-Language', 'Accept-Encoding']);
-        res.end();
-      });
+      app.use((req, res) => {
+        res.vary(['Accept', 'Accept-Language', 'Accept-Encoding'])
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Vary', 'Accept, Accept-Language, Accept-Encoding')
-      .expect(200, done);
+        .get('/')
+        .expect('Vary', 'Accept, Accept-Language, Accept-Encoding')
+        .expect(200, done)
     })
   })
 
-  describe('with a string', function(){
-    it('should set the value', function (done) {
-      var app = express();
+  describe('with a string', () => {
+    it('should set the value', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.vary('Accept');
-        res.end();
-      });
+      app.use((req, res) => {
+        res.vary('Accept')
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Vary', 'Accept')
-      .expect(200, done);
+        .get('/')
+        .expect('Vary', 'Accept')
+        .expect(200, done)
     })
   })
 
-  describe('when the value is present', function(){
-    it('should not add it again', function (done) {
-      var app = express();
+  describe('when the value is present', () => {
+    it('should not add it again', (done) => {
+      const app = express()
 
-      app.use(function (req, res) {
-        res.vary('Accept');
-        res.vary('Accept-Encoding');
-        res.vary('Accept-Encoding');
-        res.vary('Accept-Encoding');
-        res.vary('Accept');
-        res.end();
-      });
+      app.use((req, res) => {
+        res.vary('Accept')
+        res.vary('Accept-Encoding')
+        res.vary('Accept-Encoding')
+        res.vary('Accept-Encoding')
+        res.vary('Accept')
+        res.end()
+      })
 
       request(app)
-      .get('/')
-      .expect('Vary', 'Accept, Accept-Encoding')
-      .expect(200, done);
+        .get('/')
+        .expect('Vary', 'Accept, Accept-Encoding')
+        .expect(200, done)
     })
   })
 })
diff --git a/test/support/env.js b/test/support/env.js
index 000638ceeae..c967199232e 100644
--- a/test/support/env.js
+++ b/test/support/env.js
@@ -1,3 +1,2 @@
-
-process.env.NODE_ENV = 'test';
-process.env.NO_DEPRECATION = 'body-parser,express';
+process.env.NODE_ENV = 'test'
+process.env.NO_DEPRECATION = 'body-parser,express'
diff --git a/test/support/tmpl.js b/test/support/tmpl.js
index e24b6fe773b..f26cb85583c 100644
--- a/test/support/tmpl.js
+++ b/test/support/tmpl.js
@@ -1,36 +1,36 @@
-var fs = require('node:fs');
+const fs = require('node:fs')
 
-var variableRegExp = /\$([0-9a-zA-Z\.]+)/g;
+const variableRegExp = /\$([0-9a-zA-Z.]+)/g
 
-module.exports = function renderFile(fileName, options, callback) {
-  function onReadFile(err, str) {
+module.exports = function renderFile (fileName, options, callback) {
+  function onReadFile (err, str) {
     if (err) {
-      callback(err);
-      return;
+      callback(err)
+      return
     }
 
     try {
-      str = str.replace(variableRegExp, generateVariableLookup(options));
+      str = str.replace(variableRegExp, generateVariableLookup(options))
     } catch (e) {
-      err = e;
+      err = e
       err.name = 'RenderError'
     }
 
-    callback(err, str);
+    callback(err, str)
   }
 
-  fs.readFile(fileName, 'utf8', onReadFile);
-};
+  fs.readFile(fileName, 'utf8', onReadFile)
+}
 
-function generateVariableLookup(data) {
-  return function variableLookup(str, path) {
-    var parts = path.split('.');
-    var value = data;
+function generateVariableLookup (data) {
+  return function variableLookup (str, path) {
+    const parts = path.split('.')
+    let value = data
 
-    for (var i = 0; i < parts.length; i++) {
-      value = value[parts[i]];
+    for (let i = 0; i < parts.length; i++) {
+      value = value[parts[i]]
     }
 
-    return value;
-  };
+    return value
+  }
 }
diff --git a/test/support/utils.js b/test/support/utils.js
index fb816b08000..891846eb4aa 100644
--- a/test/support/utils.js
+++ b/test/support/utils.js
@@ -1,11 +1,10 @@
-
 /**
  * Module dependencies.
  * @private
  */
 
-var assert = require('node:assert');
-const { Buffer } = require('node:buffer');
+const assert = require('node:assert')
+const { Buffer } = require('node:buffer')
 
 /**
  * Module exports.
@@ -15,7 +14,7 @@ const { Buffer } = require('node:buffer');
 exports.shouldHaveBody = shouldHaveBody
 exports.shouldHaveHeader = shouldHaveHeader
 exports.shouldNotHaveBody = shouldNotHaveBody
-exports.shouldNotHaveHeader = shouldNotHaveHeader;
+exports.shouldNotHaveHeader = shouldNotHaveHeader
 exports.shouldSkipQuery = shouldSkipQuery
 
 /**
@@ -27,7 +26,7 @@ exports.shouldSkipQuery = shouldSkipQuery
 
 function shouldHaveBody (buf) {
   return function (res) {
-    var body = !Buffer.isBuffer(res.body)
+    const body = !Buffer.isBuffer(res.body)
       ? Buffer.from(res.text)
       : res.body
     assert.ok(body, 'response has body')
@@ -66,21 +65,20 @@ function shouldNotHaveBody () {
  * @param {string} header Header name to check
  * @returns {function}
  */
-function shouldNotHaveHeader(header) {
+function shouldNotHaveHeader (header) {
   return function (res) {
-    assert.ok(!(header.toLowerCase() in res.headers), 'should not have header ' + header);
-  };
+    assert.ok(!(header.toLowerCase() in res.headers), 'should not have header ' + header)
+  }
 }
 
-function getMajorVersion(versionString) {
-  return versionString.split('.')[0];
+function getMajorVersion (versionString) {
+  return versionString.split('.')[0]
 }
 
-function shouldSkipQuery(versionString) {
+function shouldSkipQuery (versionString) {
   // Skipping HTTP QUERY tests below Node 22, QUERY wasn't fully supported by Node until 22
   // we could update this implementation to run on supported versions of 21 once they exist
   // upstream tracking https://github.com/nodejs/node/issues/51562
   // express tracking issue: https://github.com/expressjs/express/issues/5615
   return Number(getMajorVersion(versionString)) < 22
 }
-
diff --git a/test/utils.js b/test/utils.js
index 1c06036aa98..654fec42615 100644
--- a/test/utils.js
+++ b/test/utils.js
@@ -1,26 +1,26 @@
 'use strict'
 
-var assert = require('node:assert');
-const { Buffer } = require('node:buffer');
-var utils = require('../lib/utils');
+const assert = require('node:assert')
+const { Buffer } = require('node:buffer')
+const utils = require('../lib/utils')
 
-describe('utils.etag(body, encoding)', function(){
-  it('should support strings', function(){
+describe('utils.etag(body, encoding)', () => {
+  it('should support strings', () => {
     assert.strictEqual(utils.etag('express!'),
       '"8-O2uVAFaQ1rZvlKLT14RnuvjPIdg"')
   })
 
-  it('should support utf8 strings', function(){
+  it('should support utf8 strings', () => {
     assert.strictEqual(utils.etag('express❤', 'utf8'),
       '"a-JBiXf7GyzxwcrxY4hVXUwa7tmks"')
   })
 
-  it('should support buffer', function(){
+  it('should support buffer', () => {
     assert.strictEqual(utils.etag(Buffer.from('express!')),
       '"8-O2uVAFaQ1rZvlKLT14RnuvjPIdg"')
   })
 
-  it('should support empty string', function(){
+  it('should support empty string', () => {
     assert.strictEqual(utils.etag(''),
       '"0-2jmj7l5rSw0yVb/vlWAYkK/YBwk"')
   })
@@ -28,55 +28,54 @@ describe('utils.etag(body, encoding)', function(){
 
 describe('utils.normalizeType acceptParams method', () => {
   it('should handle a type with a malformed parameter and break the loop in acceptParams', () => {
-    const result = utils.normalizeType('text/plain;invalid');
-    assert.deepEqual(result,{
+    const result = utils.normalizeType('text/plain;invalid')
+    assert.deepEqual(result, {
       value: 'text/plain',
       quality: 1,
       params: {} // No parameters are added since "invalid" has no "="
-    });
-  });
-});
-
+    })
+  })
+})
 
-describe('utils.setCharset(type, charset)', function () {
-  it('should do anything without type', function () {
-    assert.strictEqual(utils.setCharset(), undefined);
-  });
+describe('utils.setCharset(type, charset)', () => {
+  it('should do anything without type', () => {
+    assert.strictEqual(utils.setCharset(), undefined)
+  })
 
-  it('should return type if not given charset', function () {
-    assert.strictEqual(utils.setCharset('text/html'), 'text/html');
-  });
+  it('should return type if not given charset', () => {
+    assert.strictEqual(utils.setCharset('text/html'), 'text/html')
+  })
 
-  it('should keep charset if not given charset', function () {
-    assert.strictEqual(utils.setCharset('text/html; charset=utf-8'), 'text/html; charset=utf-8');
-  });
+  it('should keep charset if not given charset', () => {
+    assert.strictEqual(utils.setCharset('text/html; charset=utf-8'), 'text/html; charset=utf-8')
+  })
 
-  it('should set charset', function () {
-    assert.strictEqual(utils.setCharset('text/html', 'utf-8'), 'text/html; charset=utf-8');
-  });
+  it('should set charset', () => {
+    assert.strictEqual(utils.setCharset('text/html', 'utf-8'), 'text/html; charset=utf-8')
+  })
 
-  it('should override charset', function () {
-    assert.strictEqual(utils.setCharset('text/html; charset=iso-8859-1', 'utf-8'), 'text/html; charset=utf-8');
-  });
-});
+  it('should override charset', () => {
+    assert.strictEqual(utils.setCharset('text/html; charset=iso-8859-1', 'utf-8'), 'text/html; charset=utf-8')
+  })
+})
 
-describe('utils.wetag(body, encoding)', function(){
-  it('should support strings', function(){
+describe('utils.wetag(body, encoding)', () => {
+  it('should support strings', () => {
     assert.strictEqual(utils.wetag('express!'),
       'W/"8-O2uVAFaQ1rZvlKLT14RnuvjPIdg"')
   })
 
-  it('should support utf8 strings', function(){
+  it('should support utf8 strings', () => {
     assert.strictEqual(utils.wetag('express❤', 'utf8'),
       'W/"a-JBiXf7GyzxwcrxY4hVXUwa7tmks"')
   })
 
-  it('should support buffer', function(){
+  it('should support buffer', () => {
     assert.strictEqual(utils.wetag(Buffer.from('express!')),
       'W/"8-O2uVAFaQ1rZvlKLT14RnuvjPIdg"')
   })
 
-  it('should support empty string', function(){
+  it('should support empty string', () => {
     assert.strictEqual(utils.wetag(''),
       'W/"0-2jmj7l5rSw0yVb/vlWAYkK/YBwk"')
   })