Switch to webpack v3.

There are some sections for webpack v4 which are commented out (and some
sections for v3 that would need to be removed).  When karma-webpack v4
is official, we may want to switch to version 4.

external.config.js

@@ -1,7 +1,12 @@
 var path = require('path');
-var webpack = require('webpack');
+var UglifyJsPlugin = require('uglifyjs-webpack-plugin');
 
 module.exports = {
+  /* webpack 4
+  mode: 'production',
+   */
+  performance: {hints: false},
+  cache: true,
   context: path.join(__dirname, 'src'),
   entry: {
     'geo.ext': './vendor.js',
@@ -18,18 +23,41 @@ module.exports = {
       hammerjs: 'hammerjs/hammer.js'
     }
   },
+  /* webpack 3 */
   plugins: [
-    new webpack.optimize.UglifyJsPlugin({
+    new UglifyJsPlugin({
       include: /\.min\.js$/,
-      minimize: true,
-      comments: /@(license|copyright)/
+      parallel: true,
+      uglifyOptions: {
+        compress: true,
+        comments: /@(license|copyright)/
+      },
+      sourceMap: true
     })
   ],
+  /* end webpack 3 */
+  /* webpack 4
+  optimization: {
+    minimizer: [
+      new UglifyJsPlugin({
+        include: /\.min\.js$/,
+        parallel: true,
+        uglifyOptions: {
+          compress: true,
+          comments: /@(license|copyright)/
+        },
+        sourceMap: true
+      })
+    ]
+  },
+  */
   module: {
-    loaders: [{
-      test: require.resolve('d3'), loader: 'expose?d3'
+    rules: [{
+      test: require.resolve('d3'),
+      use: ['expose-loader?d3']
     }, {
-      test: require.resolve('hammerjs'), loader: 'expose?hammerjs'
+      test: require.resolve('hammerjs'),
+      use: ['expose-loader?hammerjs']
     }]
   }
 };

karma-base.js

@@ -249,6 +249,24 @@ var FirefoxPrefs = {
 };
 
 module.exports = function (config) {
+  webpack_config.plugins.push(function () {
+    this.plugin('done', function (stats) {
+      if (stats.compilation.warnings.length) {
+        // Log each of the warnings
+        stats.compilation.warnings.forEach(function (warning) {
+          console.log(warning.message || warning);
+        });
+        // Pretend no assets were generated. This prevents the tests
+        // from running making it clear that there were warnings.
+        stats.stats = [{
+          toJson: function () {
+            return this;
+          },
+          assets: []
+        }];
+      }
+    });
+  });
   var newConfig = {
     autoWatch: false,
     files: [
@@ -300,7 +318,7 @@ module.exports = function (config) {
           '--kiosk',
           '--incognito',
           '--translate-script-url=""',
-          '--proxy-pac-url=' + config.protocol + '//' + config.hostname + ':' + config.port + '/testdata/proxy-for-tests.pac'
+          '--proxy-pac-url=' + config.protocol + '//' + (config.hostname || '127.0.0.1') + ':' + config.port + '/testdata/proxy-for-tests.pac'
         ])
       },
       FirefoxHeadlessTouch: {
@@ -315,7 +333,7 @@ module.exports = function (config) {
         prefs: Object.assign({
           // enable proxy
           'network.proxy.type': 2,
-          'network.proxy.autoconfig_url': config.protocol + '//' + config.hostname + ':' + config.port + '/testdata/proxy-for-tests.pac',
+          'network.proxy.autoconfig_url': config.protocol + '//' + (config.hostname || '127.0.0.1') + ':' + config.port + '/testdata/proxy-for-tests.pac',
           // enable touch
           'dom.w3c_touch_events.enabled': 1
         }, FirefoxPrefs)
@@ -347,13 +365,17 @@ module.exports = function (config) {
       }
     },
     webpack: {
+      /* webpack 4
+      mode: 'production',
+       */
+      performance: {hints: false},
       cache: true,
       devtool: 'inline-source-map',
       module: {
-        loaders: webpack_config.module.loaders
+        rules: webpack_config.module.rules
       },
       resolve: webpack_config.resolve,
-      plugins: webpack_config.exposed_plugins
+      plugins: webpack_config.plugins
     },
     webpackMiddleware: {
       stats: 'errors-only'

karma-cov.conf.js

@@ -41,13 +41,11 @@ module.exports = function (config) {
       {type: 'text'}
     ]
   };
-  karma_config.webpack.module.preLoaders = [
-    {
-      test: /\.js$/,
-      include: path.resolve('src/'),
-      loader: 'istanbul-instrumenter'
-    }
-  ];
+  karma_config.webpack.module.rules.unshift({
+    test: /\.js$/,
+    include: path.resolve('src/'),
+    use: ['istanbul-instrumenter-loader']
+  });
 
   config.set(karma_config);
 };