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

// @remove-on-eject-begin
/**
 * Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 */
// @remove-on-eject-end
'use strict';

const autoprefixer = require('autoprefixer');
const path = require('path');
const webpack = require('webpack');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const CaseSensitivePathsPlugin = require('case-sensitive-paths-webpack-plugin');
const InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
const WatchMissingNodeModulesPlugin = require('react-dev-utils/WatchMissingNodeModulesPlugin');
const eslintFormatter = require('react-dev-utils/eslintFormatter');
const ModuleScopePlugin = require('react-dev-utils/ModuleScopePlugin');
const getClientEnvironment = require('./env');
const paths = require('./paths');

// Webpack uses `publicPath` to determine where the app is being served from.
// In development, we always serve from the root. This makes config easier.
const publicPath = '/';
// `publicUrl` is just like `publicPath`, but we will provide it to our app
// as %PUBLIC_URL% in `index.html` and `process.env.PUBLIC_URL` in JavaScript.
// Omit trailing slash as %PUBLIC_PATH%/xyz looks better than %PUBLIC_PATH%xyz.
const publicUrl = '';
// Get environment variables to inject into our app.
const env = getClientEnvironment(publicUrl);

// Options for PostCSS as we reference these options twice
// Adds vendor prefixing based on your specified browser support in
// package.json
const postCSSLoaderOptions = {
  // Necessary for external CSS imports to work
  // https://github.com/facebook/create-react-app/issues/2677
  ident: 'postcss',
  plugins: () => [
    require('postcss-flexbugs-fixes'),
    autoprefixer({
      flexbox: 'no-2009',
    }),
  ],
};

// This is the development configuration.
// It is focused on developer experience and fast rebuilds.
// The production configuration is different and lives in a separate file.
module.exports = {
  // You may want 'eval' instead if you prefer to see the compiled output in DevTools.
  // See the discussion in https://github.com/facebook/create-react-app/issues/343.
  devtool: 'cheap-module-source-map',
  // These are the "entry points" to our application.
  // This means they will be the "root" imports that are included in JS bundle.
  // The first two entry points enable "hot" CSS and auto-refreshes for JS.
  entry: [
    // We ship a few polyfills by default:
    require.resolve('./polyfills'),
    // Include an alternative client for WebpackDevServer. A client's job is to
    // connect to WebpackDevServer by a socket and get notified about changes.
    // When you save a file, the client will either apply hot updates (in case
    // of CSS changes), or refresh the page (in case of JS changes). When you
    // make a syntax error, this client will display a syntax error overlay.
    // Note: instead of the default WebpackDevServer client, we use a custom one
    // to bring better experience for Create React App users. You can replace
    // the line below with these two lines if you prefer the stock client:
    // require.resolve('webpack-dev-server/client') + '?/',
    // require.resolve('webpack/hot/dev-server'),
    require.resolve('react-dev-utils/webpackHotDevClient'),
    // Finally, this is your app's code:
    paths.appIndexJs,
    // We include the app code last so that if there is a runtime error during
    // initialization, it doesn't blow up the WebpackDevServer client, and
    // changing JS code would still trigger a refresh.
  ],
  output: {
    // Add /* filename */ comments to generated require()s in the output.
    pathinfo: true,
    // This does not produce a real file. It's just the virtual path that is
    // served by WebpackDevServer in development. This is the JS bundle
    // containing code from all our entry points, and the Webpack runtime.
    filename: 'static/js/bundle.js',
    // There are also additional JS chunk files if you use code splitting.
    chunkFilename: 'static/js/[name].chunk.js',
    // This is the URL that app is served from. We use "/" in development.
    publicPath: publicPath,
    // Point sourcemap entries to original disk location (format as URL on Windows)
    devtoolModuleFilenameTemplate: info =>
      path.resolve(info.absoluteResourcePath).replace(/\\/g, '/'),
  },
  resolve: {
    // This allows you to set a fallback for where Webpack should look for modules.
    // We placed these paths second because we want `node_modules` to "win"
    // if there are any conflicts. This matches Node resolution mechanism.
    // https://github.com/facebook/create-react-app/issues/253
    modules: ['node_modules'].concat(
      // It is guaranteed to exist because we tweak it in `env.js`
      process.env.NODE_PATH.split(path.delimiter).filter(Boolean)
    ),
    // These are the reasonable defaults supported by the Node ecosystem.
    // We also include JSX as a common component filename extension to support
    // some tools, although we do not recommend using it, see:
    // https://github.com/facebook/create-react-app/issues/290
    // `web` extension prefixes have been added for better support
    // for React Native Web.
    extensions: ['.web.js', '.mjs', '.js', '.json', '.web.jsx', '.jsx'],
    alias: {
      // @remove-on-eject-begin
      // Resolve Babel runtime relative to react-scripts.
      // It usually still works on npm 3 without this but it would be
      // unfortunate to rely on, as react-scripts could be symlinked,
      // and thus @babel/runtime might not be resolvable from the source.
      '@babel/runtime': path.dirname(
        require.resolve('@babel/runtime/package.json')
      ),
      // @remove-on-eject-end
      // Support React Native Web
      // https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
      'react-native': 'react-native-web',
    },
    plugins: [
      // Prevents users from importing files from outside of src/ (or node_modules/).
      // This often causes confusion because we only process files within src/ with babel.
      // To fix this, we prevent you from importing files out of src/ -- if you'd like to,
      // please link the files into your node_modules/ and let module-resolution kick in.
      // Make sure your source files are compiled, as they will not be processed in any way.
      new ModuleScopePlugin(paths.appSrc, [paths.appPackageJson]),
    ],
  },
  module: {
    strictExportPresence: true,
    rules: [
      // Disable require.ensure as it's not a standard language feature.
      { parser: { requireEnsure: false } },

      // First, run the linter.
      // It's important to do this before Babel processes the JS.
      {
        test: /\.(js|jsx|mjs)$/,
        enforce: 'pre',
        use: [
          {
            options: {
              formatter: eslintFormatter,
              eslintPath: require.resolve('eslint'),
              baseConfig: {
                extends: [require.resolve('eslint-config-react-app')],
              },
              // @remove-on-eject-begin
              ignore: false,
              useEslintrc: false,
              // @remove-on-eject-end
            },
            loader: require.resolve('eslint-loader'),
          },
        ],
        include: paths.srcPaths,
        exclude: [/[/\\\\]node_modules[/\\\\]/],
      },
      {
        // "oneOf" will traverse all following loaders until one will
        // match the requirements. When no loader matches it will fall
        // back to the "file" loader at the end of the loader list.
        oneOf: [
          // "url" loader works like "file" loader except that it embeds assets
          // smaller than specified limit in bytes as data URLs to avoid requests.
          // A missing `test` is equivalent to a match.
          {
            test: [/\.bmp$/, /\.gif$/, /\.jpe?g$/, /\.png$/],
            loader: require.resolve('url-loader'),
            options: {
              limit: 10000,
              name: 'static/media/[name].[hash:8].[ext]',
            },
          },
          // Process application JS with Babel.
          // The preset includes JSX, Flow, and some ESnext features.
          {
            test: /\.(js|jsx|mjs)$/,
            include: paths.srcPaths,
            exclude: [/[/\\\\]node_modules[/\\\\]/],
            use: [
              // This loader parallelizes code compilation, it is optional but
              // improves compile time on larger projects
              require.resolve('thread-loader'),
              {
                loader: require.resolve('babel-loader'),
                options: {
                  // @remove-on-eject-begin
                  babelrc: false,
                  // @remove-on-eject-end
                  presets: [require.resolve('babel-preset-react-app')],
                  // This is a feature of `babel-loader` for webpack (not Babel itself).
                  // It enables caching results in ./node_modules/.cache/babel-loader/
                  // directory for faster rebuilds.
                  cacheDirectory: true,
                  highlightCode: true,
                },
              },
            ],
          },
          // Process any JS outside of the app with Babel.
          // Unlike the application JS, we only compile the standard ES features.
          {
            test: /\.js$/,
            use: [
              // This loader parallelizes code compilation, it is optional but
              // improves compile time on larger projects
              require.resolve('thread-loader'),
              {
                loader: require.resolve('babel-loader'),
                options: {
                  babelrc: false,
                  compact: false,
                  presets: [
                    require.resolve('babel-preset-react-app/dependencies'),
                  ],
                  cacheDirectory: true,
                  highlightCode: true,
                },
              },
            ],
          },
          // "postcss" loader applies autoprefixer to our CSS.
          // "css" loader resolves paths in CSS and adds assets as dependencies.
          // "style" loader turns CSS into JS modules that inject <style> tags.
          // In production, we use a plugin to extract that CSS to a file, but
          // in development "style" loader enables hot editing of CSS.
          // By default we support CSS Modules with the extension .module.css
          {
            test: /\.css$/,
            exclude: /\.module\.css$/,
            use: [
              require.resolve('style-loader'),
              {
                loader: require.resolve('css-loader'),
                options: {
                  importLoaders: 1,
                },
              },
              {
                loader: require.resolve('postcss-loader'),
                options: postCSSLoaderOptions,
              },
            ],
          },
          // Adds support for CSS Modules (https://github.com/css-modules/css-modules)
          // using the extension .module.css
          {
            test: /\.module\.css$/,
            use: [
              require.resolve('style-loader'),
              {
                loader: require.resolve('css-loader'),
                options: {
                  importLoaders: 1,
                  modules: true,
                  localIdentName: '[path]__[name]___[local]',
                },
              },
              {
                loader: require.resolve('postcss-loader'),
                options: postCSSLoaderOptions,
              },
            ],
          },
          // Allows you to use two kinds of imports for SVG:
          // import logoUrl from './logo.svg'; gives you the URL.
          // import { ReactComponent as Logo } from './logo.svg'; gives you a component.
          {
            test: /\.svg$/,
            use: [
              {
                loader: require.resolve('babel-loader'),
                options: {
                  // @remove-on-eject-begin
                  babelrc: false,
                  // @remove-on-eject-end
                  presets: [require.resolve('babel-preset-react-app')],
                  cacheDirectory: true,
                },
              },
              require.resolve('svgr/webpack'),
              {
                loader: require.resolve('file-loader'),
                options: {
                  name: 'static/media/[name].[hash:8].[ext]',
                },
              },
            ],
          },
          // "file" loader makes sure those assets get served by WebpackDevServer.
          // When you `import` an asset, you get its (virtual) filename.
          // In production, they would get copied to the `build` folder.
          // This loader doesn't use a "test" so it will catch all modules
          // that fall through the other loaders.
          {
            // Exclude `js` files to keep "css" loader working as it injects
            // its runtime that would otherwise be processed through "file" loader.
            // Also exclude `html` and `json` extensions so they get processed
            // by webpacks internal loaders.
            exclude: [/\.(js|jsx|mjs)$/, /\.html$/, /\.json$/],
            loader: require.resolve('file-loader'),
            options: {
              name: 'static/media/[name].[hash:8].[ext]',
            },
          },
        ],
      },
      // ** STOP ** Are you adding a new loader?
      // Make sure to add the new loader(s) before the "file" loader.
    ],
  },
  plugins: [
    // Makes some environment variables available in index.html.
    // The public URL is available as %PUBLIC_URL% in index.html, e.g.:
    // <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
    // In development, this will be an empty string.
    new InterpolateHtmlPlugin(env.raw),
    // Generates an `index.html` file with the <script> injected.
    new HtmlWebpackPlugin({
      inject: true,
      template: paths.appHtml,
    }),
    // Add module names to factory functions so they appear in browser profiler.
    new webpack.NamedModulesPlugin(),
    // Makes some environment variables available to the JS code, for example:
    // if (process.env.NODE_ENV === 'development') { ... }. See `./env.js`.
    new webpack.DefinePlugin(env.stringified),
    // This is necessary to emit hot updates (currently CSS only):
    new webpack.HotModuleReplacementPlugin(),
    // Watcher doesn't work well if you mistype casing in a path so we use
    // a plugin that prints an error when you attempt to do this.
    // See https://github.com/facebook/create-react-app/issues/240
    new CaseSensitivePathsPlugin(),
    // If you require a missing module and then `npm install` it, you still have
    // to restart the development server for Webpack to discover it. This plugin
    // makes the discovery automatic so you don't have to restart.
    // See https://github.com/facebook/create-react-app/issues/186
    new WatchMissingNodeModulesPlugin(paths.appNodeModules),
    // 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.
  node: {
    dgram: 'empty',
    fs: 'empty',
    net: 'empty',
    tls: 'empty',
    child_process: 'empty',
  },
  // Turn off performance hints during development because we don't do any
  // splitting or minification in interest of speed. These warnings become
  // cumbersome.
  performance: {
    hints: false,
  },
};