Force rebuild after npm install

Fixes #186

config/webpack.config.dev.js

@@ -12,6 +12,7 @@ var autoprefixer = require('autoprefixer');
 var webpack = require('webpack');
 var HtmlWebpackPlugin = require('html-webpack-plugin');
 var CaseSensitivePathsPlugin = require('case-sensitive-paths-webpack-plugin');
+var WatchMissingNodeModulesPlugin = require('../scripts/utils/WatchMissingNodeModulesPlugin');
 var paths = require('./paths');
 
 module.exports = {
@@ -107,6 +108,7 @@ module.exports = {
     new webpack.DefinePlugin({ 'process.env.NODE_ENV': '"development"' }),
     // Note: only CSS is currently hot reloaded
     new webpack.HotModuleReplacementPlugin(),
-    new CaseSensitivePathsPlugin()
+    new CaseSensitivePathsPlugin(),
+    new WatchMissingNodeModulesPlugin(paths.appNodeModules)
   ]
 };

scripts/eject.js

@@ -44,7 +44,8 @@ prompt(
     path.join('scripts', 'build.js'),
     path.join('scripts', 'start.js'),
     path.join('scripts', 'utils', 'chrome.applescript'),
-    path.join('scripts', 'utils', 'prompt.js')
+    path.join('scripts', 'utils', 'prompt.js'),
+    path.join('scripts', 'utils', 'WatchMissingNodeModulesPlugin.js')
   ];
 
   // Ensure that the app folder is clean and we won't override any files

scripts/utils/WatchMissingNodeModulesPlugin.js

@@ -0,0 +1,33 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+// This Webpack plugin ensures `npm install <library>` forces a project rebuild.
+// We’re not sure why this isn't Webpack's default behavior.
+// See https://github.com/facebookincubator/create-react-app/issues/186.
+
+function WatchMissingNodeModulesPlugin(nodeModulesPath) {
+  this.nodeModulesPath = nodeModulesPath;
+}
+
+WatchMissingNodeModulesPlugin.prototype.apply = function (compiler) {
+  compiler.plugin('emit', (compilation, callback) => {
+    var missingDeps = compilation.missingDependencies;
+    var nodeModulesPath = this.nodeModulesPath;
+
+    // If any missing files are expected to appear in node_modules...
+    if (missingDeps.some(file => file.indexOf(nodeModulesPath) !== -1)) {
+      // ...tell webpack to watch node_modules recursively until they appear.
+      compilation.contextDependencies.push(nodeModulesPath);
+    }
+
+    callback();
+  });
+}
+
+module.exports = WatchMissingNodeModulesPlugin;