Switch npm package to ESM

Change the npm package type to `module`, so that `.js` files are treated as ESM
by default. All of the JS scripts that run in Node had already been converted to
ESM, except for the Karma config, which has to remain CommonJS.

.eslintrc

@@ -6,9 +6,9 @@
   },
   "overrides": [
     {
-      "files": ["*.mjs"],
+      "files": ["*.js"],
+      "excludedFiles": ["h/**"],
       "env": { "node": true },
-      "parserOptions": { "sourceType": "module" }
     }
   ]
 }

Dockerfile

@@ -10,7 +10,7 @@ COPY .yarn ./.yarn
 RUN yarn install --immutable
 
 # Build h js/css.
-COPY .babelrc gulpfile.mjs rollup.config.mjs ./
+COPY .babelrc gulpfile.js rollup.config.js ./
 COPY h/static ./h/static
 RUN yarn build
 

gulpfile.mjs → gulpfile.js

@@ -12,8 +12,8 @@ import svgmin from 'gulp-svgmin';
 
 const IS_PRODUCTION_BUILD = process.env.NODE_ENV === 'production';
 
-gulp.task('build-js', () => buildJS('./rollup.config.mjs'));
-gulp.task('watch-js', () => watchJS('./rollup.config.mjs'));
+gulp.task('build-js', () => buildJS('./rollup.config.js'));
+gulp.task('watch-js', () => watchJS('./rollup.config.js'));
 
 gulp.task('build-css', () =>
   buildCSS([
@@ -107,8 +107,8 @@ gulp.task(
 gulp.task('test', () =>
   runTests({
     bootstrapFile: './h/static/scripts/tests/bootstrap.js',
-    karmaConfig: './h/static/scripts/karma.config.js',
-    rollupConfig: './rollup-tests.config.mjs',
+    karmaConfig: './h/static/scripts/karma.config.cjs',
+    rollupConfig: './rollup-tests.config.js',
     testsPattern: 'h/static/scripts/**/*-test.js',
   }),
 );

package.json

@@ -2,11 +2,12 @@
   "name": "h",
   "private": true,
   "version": "0.0.0",
+  "type": "module",
   "description": "The Internet, peer reviewed.",
   "scripts": {
     "build": "gulp build",
-    "checkformatting": "prettier --check *.mjs h/static/scripts",
-    "format": "prettier --list-different --write *.mjs h/static/scripts",
+    "checkformatting": "prettier --check *.js h/static/scripts",
+    "format": "prettier --list-different --write *.js h/static/scripts",
     "lint": "eslint h/static/scripts",
     "test": "gulp test"
   },