enable manifest plugin on dev

packages/react-scripts/config/webpack.config.dev.js

@@ -19,6 +19,7 @@ const eslintFormatter = require('react-dev-utils/eslintFormatter');
 const ModuleScopePlugin = require('react-dev-utils/ModuleScopePlugin');
 const getClientEnvironment = require('./env');
 const paths = require('./paths');
+const ManifestPlugin = require('webpack-manifest-plugin');
 
 // Webpack uses `publicPath` to determine where the app is being served from.
 // In development, we always serve from the root. This makes config easier.
@@ -338,6 +339,13 @@ module.exports = {
     // https://github.com/jmblog/how-to-optimize-momentjs-with-webpack
     // You can remove this if you don't use Moment.js:
     new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/),
+    // Generate a manifest file which contains a mapping of all asset filenames
+    // to their corresponding output file so that tools can pick it up without
+    // having to parse `index.html`.
+    new ManifestPlugin({
+      fileName: 'asset-manifest.json',
+      publicPath: publicPath,
+    }),
   ],
   // Some libraries import Node modules but don't use them in the browser.
   // Tell Webpack to provide empty mocks for them so importing them works.