diff --git a/index.js b/index.js
index 5ca9cec..a116c49 100644
--- a/index.js
+++ b/index.js
@@ -1,152 +1,187 @@
-var staticModule = require('static-module');
-var quote = require('quote-stream');
-var through = require('through2');
-var fs = require('fs');
-var path = require('path');
-var resolve = require('resolve');
+var staticModule = require("static-module");
+var quote = require("quote-stream");
+var through = require("through2");
+var fs = require("fs");
+var path = require("path");
+var resolve = require("resolve");
 
 module.exports = function (file, opts) {
-    if (/\.json$/.test(file)) return through();
-    
-    function resolver (p) {
-        return resolve.sync(p, { basedir: path.dirname(file) });
-    }
-    var vars = {
-        __filename: file,
-        __dirname: path.dirname(file),
-        require: { resolve: resolver }
-    };
-    if (!opts) opts = {};
-    if (opts.vars) Object.keys(opts.vars).forEach(function (key) {
-        vars[key] = opts.vars[key];
+  if (/\.json$/.test(file)) return through();
+
+  function resolver(p) {
+    return resolve.sync(p, { basedir: path.dirname(file) });
+  }
+  function convertTransformOptionToStream(f, args) {
+    if (typeof f === "function") {
+      return f.apply(null, args);
+    }
+
+    return f;
+  }
+  var vars = {
+    __filename: file,
+    __dirname: path.dirname(file),
+    require: { resolve: resolver },
+  };
+  if (!opts) opts = {};
+  if (opts.vars)
+    Object.keys(opts.vars).forEach(function (key) {
+      vars[key] = opts.vars[key];
     });
-    
-    var sm = staticModule(
-        {
-            fs: {
-                readFileSync: readFileSync,
-                readFile: readFile,
-                readdirSync: readdirSync,
-                readdir: readdir
-            }
-        },
-        {
-            vars: vars,
-            varModules: { path: path },
-            parserOpts: opts && opts.parserOpts,
-            sourceMap: opts && (opts.sourceMap || opts._flags && opts._flags.debug),
-            inputFilename: file
-        }
-    );
-    return sm;
-    
-    function readFile (file, enc, cb) {
-        if (typeof enc === 'function') {
-            cb = enc;
-            enc = null;
-        }
-        if (enc && typeof enc === 'object' && enc.encoding) {
-            enc = enc.encoding;
-        }
-        var isBuffer = false;
-        if (enc === null || enc === undefined) {
-            isBuffer = true;
-            enc = 'base64';
-        }
-        
-        var stream = through(write, end);
-        stream.push('process.nextTick(function(){(' + cb + ')(null,');
-        if (isBuffer) stream.push('Buffer(');
-        
-        var s = fs.createReadStream(file, { encoding: enc });
-        s.on('error', function (err) { sm.emit('error', err) });
-        return s.pipe(quote()).pipe(stream);
-        
-        function write (buf, enc, next) {
-            this.push(buf);
-            next();
-        }
-        function end (next) {
-            if (isBuffer) this.push(',"base64")');
-            this.push(')})');
-            this.push(null);
-            sm.emit('file', file);
-            next()
-        }
+
+  var sm = staticModule(
+    {
+      fs: {
+        readFileSync: readFileSync,
+        readFile: readFile,
+        readdirSync: readdirSync,
+        readdir: readdir,
+      },
+    },
+    {
+      vars: vars,
+      varModules: { path: path },
+      parserOpts: opts && opts.parserOpts,
+      sourceMap: opts && (opts.sourceMap || (opts._flags && opts._flags.debug)),
+      inputFilename: file,
+    }
+  );
+  return sm;
+
+  function readFile(file, enc, cb) {
+    if (file === undefined) {
+      throw new Error('file is not resolvable');
     }
     
-    function readFileSync (file, enc) {
-        var isBuffer = false;
-        if (enc === null || enc === undefined) {
-            isBuffer = true;
-            enc = 'base64';
-        }
-        if (enc && typeof enc === 'object' && enc.encoding) {
-            enc = enc.encoding;
-        }
-        var stream = fs.createReadStream(file,  { encoding: enc })
-            .on('error', function (err) { sm.emit('error', err) })
-            .pipe(quote()).pipe(through(write, end))
-        ;
-        if (isBuffer) {
-            stream.push('Buffer(');
-        }
-        return stream;
-        
-        function write (buf, enc, next) {
-            this.push(buf);
-            next();
-        }
-        function end (next) {
-            if (isBuffer) this.push(',"base64")');
-            this.push(null);
-            sm.emit('file', file);
-            next();
-        }
+    if (typeof enc === "function") {
+      cb = enc;
+      enc = null;
+    }
+    if (enc && typeof enc === "object" && enc.encoding) {
+      enc = enc.encoding;
+    }
+    var isBuffer = false;
+    if (enc === null || enc === undefined) {
+      isBuffer = true;
+      enc = "base64";
+    }
+
+    var stream = through(write, end);
+    stream.push("process.nextTick(function(){(" + cb + ")(null,");
+    if (isBuffer) stream.push("Buffer(");
+
+    var s = fs.createReadStream(file, { encoding: enc });
+    s.on("error", function (err) {
+      sm.emit("error", err);
+    });
+
+    if (opts.readFileTransform) {
+      s = s.pipe(
+        convertTransformOptionToStream(opts.readFileTransform, [file])
+      );
+    }
+
+    return s.pipe(quote()).pipe(stream);
+
+    function write(buf, enc, next) {
+      this.push(buf);
+      next();
+    }
+    function end(next) {
+      if (isBuffer) this.push(',"base64")');
+      this.push(")})");
+      this.push(null);
+      sm.emit("file", file);
+      next();
+    }
+  }
+
+  function readFileSync(file, enc) {
+    if (file === undefined) {
+      throw new Error('file is not resolvable');
     }
     
-    function readdir(path, cb) {
-        var stream = through(write, end);
-
-        stream.push('process.nextTick(function(){(' + cb + ')(null,');
-        fs.readdir(path, function (err, src) {
-            if (err) {
-                stream.emit('error', err);
-                return;
-            }
-            stream.push(JSON.stringify(src));
-            stream.end(')})');
-        });
-        return stream;
-
-        function write (buf, enc, next) {
-            this.push(buf);
-            next();
-        }
-        function end (next) {
-            this.push(null);
-            next();
-        }
-    }
-
-    function readdirSync (path) {
-        var stream = through(write, end);
-        fs.readdir(path, function (err, src) {
-            if (err) {
-                stream.emit('error', err);
-                return;
-            }
-            stream.end(JSON.stringify(src));
-        });
-        return stream;
-
-        function write (buf, enc, next) {
-            this.push(buf);
-            next();
-        }
-        function end (next) {
-            this.push(null);
-            next();
-        }
+    var isBuffer = false;
+    if (enc === null || enc === undefined) {
+      isBuffer = true;
+      enc = "base64";
+    }
+    if (enc && typeof enc === "object" && enc.encoding) {
+      enc = enc.encoding;
+    }
+    var stream = fs
+      .createReadStream(file, { encoding: enc })
+      .on("error", function (err) {
+        sm.emit("error", err);
+      });
+
+    if (opts.readFileTransform) {
+      stream = stream.pipe(
+        convertTransformOptionToStream(opts.readFileTransform, [file])
+      );
+    }
+
+    stream = stream.pipe(quote()).pipe(through(write, end));
+
+    if (isBuffer) {
+      stream.push("Buffer(");
+    }
+    return stream;
+
+    function write(buf, enc, next) {
+      this.push(buf);
+      next();
+    }
+    function end(next) {
+      if (isBuffer) this.push(',"base64")');
+      this.push(null);
+      sm.emit("file", file);
+      next();
+    }
+  }
+
+  function readdir(path, cb) {
+    var stream = through(write, end);
+
+    stream.push("process.nextTick(function(){(" + cb + ")(null,");
+    fs.readdir(path, function (err, src) {
+      if (err) {
+        stream.emit("error", err);
+        return;
+      }
+      stream.push(JSON.stringify(src));
+      stream.end(")})");
+    });
+    return stream;
+
+    function write(buf, enc, next) {
+      this.push(buf);
+      next();
+    }
+    function end(next) {
+      this.push(null);
+      next();
+    }
+  }
+
+  function readdirSync(path) {
+    var stream = through(write, end);
+    fs.readdir(path, function (err, src) {
+      if (err) {
+        stream.emit("error", err);
+        return;
+      }
+      stream.end(JSON.stringify(src));
+    });
+    return stream;
+
+    function write(buf, enc, next) {
+      this.push(buf);
+      next();
+    }
+    function end(next) {
+      this.push(null);
+      next();
     }
+  }
 };
diff --git a/readme.markdown b/readme.markdown
index 19058a8..e8d714a 100644
--- a/readme.markdown
+++ b/readme.markdown
@@ -16,15 +16,15 @@ projects.
 
 for a main.js:
 
-``` js
-var fs = require('fs');
-var html = fs.readFileSync(__dirname + '/robot.html', 'utf8');
+```js
+var fs = require("fs");
+var html = fs.readFileSync(__dirname + "/robot.html", "utf8");
 console.log(html);
 ```
 
 and a robot.html:
 
-``` html
+```html
 <b>beep boop</b>
 ```
 
@@ -38,65 +38,67 @@ $ browserify -t brfs example/main.js > bundle.js
 
 now in the bundle output file,
 
-``` js
-var html = fs.readFileSync(__dirname + '/robot.html', 'utf8');
+```js
+var html = fs.readFileSync(__dirname + "/robot.html", "utf8");
 ```
 
 turns into:
 
-``` js
+```js
 var html = "<b>beep boop</b>\n";
 ```
 
 ## or with the api
 
-``` js
-var browserify = require('browserify');
-var fs = require('fs');
+```js
+var browserify = require("browserify");
+var fs = require("fs");
 
-var b = browserify('example/main.js');
-b.transform('brfs');
+var b = browserify("example/main.js");
+b.transform("brfs");
 
-b.bundle().pipe(fs.createWriteStream('bundle.js'));
+b.bundle().pipe(fs.createWriteStream("bundle.js"));
 ```
 
 ## async
 
 You can also use `fs.readFile()`:
 
-``` js
-var fs = require('fs');
-fs.readFile(__dirname + '/robot.html', 'utf8', function (err, html) {
-    console.log(html);
+```js
+var fs = require("fs");
+fs.readFile(__dirname + "/robot.html", "utf8", function (err, html) {
+  console.log(html);
 });
 ```
 
 When you run this code through brfs, it turns into:
 
-``` js
-var fs = require('fs');
-process.nextTick(function () {(function (err, html) {
+```js
+var fs = require("fs");
+process.nextTick(function () {
+  (function (err, html) {
     console.log(html);
-})(null,"<b>beep boop</b>\n")});
+  })(null, "<b>beep boop</b>\n");
+});
 ```
 
 # methods
 
 brfs looks for:
 
-* `fs.readFileSync(pathExpr, enc=null)`
-* `fs.readFile(pathExpr, enc=null, cb)`
-* `fs.readdirSync(pathExpr)`
-* `fs.readdir(pathExpr, cb)`
+- `fs.readFileSync(pathExpr, enc=null)`
+- `fs.readFile(pathExpr, enc=null, cb)`
+- `fs.readdirSync(pathExpr)`
+- `fs.readdir(pathExpr, cb)`
 
 Inside of each `pathExpr`, you can use
 [statically analyzable](http://npmjs.org/package/static-eval) expressions and
 these variables and functions:
 
-* `__dirname`
-* `__filename`
-* `path` if you `var path = require('path')` first
-* `require.resolve()`
+- `__dirname`
+- `__filename`
+- `path` if you `var path = require('path')` first
+- `require.resolve()`
 
 Just like node, the default encoding is `null` and will give back a `Buffer`.
 If you want differently-encoded file contents for your inline content you can
@@ -112,8 +114,8 @@ updated automatically.
 If you want to use this plugin directly, not through browserify, the api
 follows.
 
-``` js
-var brfs = require('brfs')
+```js
+var brfs = require("brfs");
 ```
 
 ## var tr = brfs(file, opts)
@@ -128,6 +130,9 @@ in addition to `__dirname` and `__filename`.
 `opts.parserOpts` can be used to configure the parser brfs uses,
 [acorn](https://github.com/acornjs/acorn#main-parser).
 
+`opts.readFileTransform` can be used to transform the filestream of
+the given file. For example you can minify the content.
+
 # events
 
 ## tr.on('file', function (file) {})
@@ -143,13 +148,13 @@ A tiny command-line program ships with this module to make debugging easier.
 usage:
 
   brfs file
- 
+
     Inline `fs.readFileSync()` calls from `file`, printing the transformed file
     contents to stdout.
 
   brfs
   brfs -
- 
+
     Inline `fs.readFileSync()` calls from stdin, printing the transformed file
     contents to stdout.
 
@@ -168,18 +173,18 @@ the browserify api.
 
 # gotchas
 
-Since `brfs` evaluates your source code *statically*, you can't use dynamic expressions that need to be evaluated at run time. For example:
+Since `brfs` evaluates your source code _statically_, you can't use dynamic expressions that need to be evaluated at run time. For example:
 
 ```js
 // WILL NOT WORK!
 var file = window.someFilePath;
-var str = require('fs').readFileSync(file, 'utf8');
+var str = require("fs").readFileSync(file, "utf8");
 ```
 
 Instead, you must use simpler expressions that can be resolved at build-time:
 
 ```js
-var str = require('fs').readFileSync(__dirname + '/file.txt', 'utf8');
+var str = require("fs").readFileSync(__dirname + "/file.txt", "utf8");
 ```
 
 Another gotcha: `brfs` does not yet support ES module `import` statements. See [brfs-babel](https://github.com/Jam3/brfs-babel) for an experimental replacement that supports this syntax.