Ignore Moment.js locales by default (#2187)

* Ignore Moment.js locales by default

* Update README.md

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

@@ -286,6 +286,12 @@ module.exports = {
     new ManifestPlugin({
       fileName: 'asset-manifest.json',
     }),
+    // Moment.js is an extremely popular library that bundles large locale files
+    // by default due to how Webpack interprets its code. This is a practical
+    // solution that requires the user to opt into importing specific locales.
+    // 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$/, /moment$/),
   ],
   // 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.