Replace Browserify with ES modules

bouncer has only a small amount of JavaScript and used Browserify purely
as a module system provider. With our currently supported browsers and
current version of Karma we can just use native ES modules instead.
Removing Browserify usage will allow us to trim the project's
dependencies.

 - Convert `redirect.js` and `redirect-test.js` to ES modules

 - Update Karma configuration to load JS files as modules and remove
   Browserify usage

.eslintrc

@@ -1,3 +1,6 @@
 {
-  "extends": "hypothesis"
+  "extends": "hypothesis",
+  "parserOptions": {
+    "sourceType": "module"
+  }
 }

bouncer/scripts/redirect.js

@@ -1,5 +1,3 @@
-'use strict';
-
 /**
  * Configuration information for the client-side code that detects the best way
  * to route the user to a URL with Hypothesis activated and specified
@@ -43,7 +41,7 @@ function defaultNavigateTo(url) {
  * @param {(url: string) => void} [navigateTo]
  * @param {Settings} [settings]
  */
-function redirect(navigateTo, settings) {
+export function redirect(navigateTo, settings) {
   navigateTo = navigateTo || defaultNavigateTo; // Test seam
   settings = settings || getSettings(document); // Test seam
 
@@ -84,11 +82,6 @@ function redirect(navigateTo, settings) {
   }
 }
 
-if (typeof module === 'object') {
-  // Browserify is present, this file must be being run by the tests.
-  module.exports = redirect;
-} else {
-  // Browserify is not present, this file must be being run in development or
-  // production.
+if (!('__karma__' in window)) { // Check if in test environment
   redirect();
 }

bouncer/scripts/test/redirect-test.js

@@ -1,6 +1,4 @@
-'use strict';
-
-var redirect = require('../redirect.js');
+import { redirect } from '../redirect.js';
 
 describe('#redirect', function () {
   var settings;

bouncer/templates/annotation.html.jinja2

@@ -17,7 +17,7 @@
   <script class="js-bouncer-settings" type="application/json">
     {{ data | safe }}
   </script>
-  <script>
+  <script type="module">
     {% include '../scripts/redirect.js' %}
   </script>
 {% endblock %}

karma.config.js

@@ -1,16 +1,11 @@
 module.exports = function (config) {
   config.set({
-    browserify: {
-      debug: true
-    },
     basePath: '',
-    frameworks: ['browserify', 'chai', 'mocha', 'sinon'],
+    frameworks: ['chai', 'mocha', 'sinon'],
     files: [
-      'bouncer/**/*-test.js'
+      { pattern: 'bouncer/scripts/*.js', type: 'module', included: false },
+      { pattern: 'bouncer/**/*-test.js', type: 'module' },
     ],
-    preprocessors: {
-      '**/*-test.js': ['browserify']
-    },
     reporters: ['progress'],
     port: 9876,
     colors: true,