text: var path = require('path');
  var autoprefixer = require('autoprefixer');
  var webpack = require('webpack');
  var HtmlWebpackPlugin = require('html-webpack-plugin');
  var ExtractTextPlugin = require('extract-text-webpack-plugin');
  var ManifestPlugin = require('webpack-manifest-plugin');
  var InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
  var url = require('url');
  var paths = require('./paths');
  var getClientEnvironment = require('./env');
  
  function ensureSlash(path, needsSlash) {
    var hasSlash = path.endsWith('/');
    if (hasSlash && !needsSlash) {
      return path.substr(path, path.length - 1);
    } else if (!hasSlash && needsSlash) {
      return path + '/';
    } else {
      return path;
    }
  }
  
  // We use "homepage" field to infer "public path" at which the app is served.
  // Webpack needs to know it to put the right <script> hrefs into HTML even in
  // single-page apps that may serve index.html for nested URLs like /todos/42.
  // We can't use a relative path in HTML because we don't want to load something
  // like /todos/42/static/js/bundle.7289d.js. We have to know the root.
  var homepagePath = require(paths.appPackageJson).homepage;
  var homepagePathname = homepagePath ? url.parse(homepagePath).pathname : '/';
  // Webpack uses `publicPath` to determine where the app is being served from.
  // It requires a trailing slash, or the file assets will get an incorrect path.
  var publicPath = ensureSlash(homepagePathname, true);
  // `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.
  var publicUrl = ensureSlash(homepagePathname, false);
  // Get environment variables to inject into our app.
  var env = getClientEnvironment(publicUrl);
  var appSrc = paths.appSrc;
  var nodeEnv = process.env.NODE_ENV;
  var babelEnv = process.env.BABEL_ENV;
  
  // Assert this just to be safe.
  // Development builds of React are slow and not intended for production.
  if (babelEnv !== 'production') {
    console.log(babelEnv);
    throw new Error('Production builds must have BABEL_ENV=production.');
  }
  
  // This is the production configuration.
  // It compiles slowly and is focused on producing a fast and minimal bundle.
  // The development configuration is different and lives in a separate file.
  module.exports = {
    // Don't attempt to continue if there are any errors.
    bail: true,
    // We generate sourcemaps in production. This is slow but gives good results.
    // You can exclude the *.map files from the build during deployment.
    devtool: 'source-map',
    // In production, we only want to load the polyfills and the app code.
    entry: [
      require.resolve('./polyfills'),
      paths.appIndexJs
    ],
    output: {
      // The build folder.
      path: paths.appBuild,
      // Generated JS file names (with nested folders).
      // There will be one main bundle, and one file per asynchronous chunk.
      // We don't currently advertise code splitting but Webpack supports it.
      filename: 'static/js/[name].[chunkhash:8].js',
      chunkFilename: 'static/js/[name].[chunkhash:8].chunk.js',
      // We inferred the "public path" (such as / or /my-project) from homepage.
      publicPath: publicPath
    },
    resolve: {
      root: [ paths.appSrc ],
      // This allows you to set a fallback for where Webpack should look for modules.
      // We read `NODE_PATH` environment variable in `paths.js` and pass paths here.
      // We use `fallback` instead of `root` because we want `node_modules` to "win"
      // if there any conflicts. This matches Node resolution mechanism.
      // https://github.com/facebookincubator/create-react-app/issues/253
      fallback: paths.nodePaths,
      // 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/facebookincubator/create-react-app/issues/290
      extensions: ['.js', '.json', '.jsx', ''],
      alias: {
        'config': `${appSrc}/config/config.${nodeEnv}.js`,
        // 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'
      }
    },
    
    module: {
      // First, run the linter.
      // It's important to do this before Babel processes the JS.
      preLoaders: [
        {
          test: /\.(js|jsx)$/,
          loader: 'eslint',
          include: paths.appSrc
        }
      ],
      loaders: [
        // Default loader: load all assets that are not handled
        // by other loaders with the url loader.
        // Note: This list needs to be updated with every change of extensions
        // the other loaders match.
        // E.g., when adding a loader for a new supported file extension,
        // we need to add the supported extension to this loader too.
        // Add one new line in `exclude` for each loader.
        //
        // "file" loader makes sure those assets end up in the `build` folder.
        // When you `import` an asset, you get its filename.
        // "url" loader works just like "file" loader but it also embeds
        // assets smaller than specified size as data URLs to avoid requests.
        {
          exclude: [
            /\.html$/,
            /\.(js|jsx)$/,
            /\.css$/,
            /\.json$/
          ],
          loader: 'url',
          query: {
            limit: 10000,
            name: 'static/media/[name].[hash:8].[ext]'
          }
        },
        // Process JS with Babel.
        {
          test: /\.(js|jsx)$/,
          include: paths.appSrc,
          loader: 'babel',
          
        },
        // The notation here is somewhat confusing.
        // "postcss" loader applies autoprefixer to our CSS.
        // "css" loader resolves paths in CSS and adds assets as dependencies.
        // "style" loader normally turns CSS into JS modules injecting <style>,
        // but unlike in development configuration, we do something different.
        // `ExtractTextPlugin` first applies the "postcss" and "css" loaders
        // (second argument), then grabs the result CSS and puts it into a
        // separate file in our build process. This way we actually ship
        // a single CSS file in production instead of JS code injecting <style>
        // tags. If you use code splitting, however, any async bundles will still
        // use the "style" loader inside the async code so CSS from them won't be
        // in the main CSS file.
        {
          test: /\.css$/,
          loader: ExtractTextPlugin.extract('style', 'css?importLoaders=1!postcss')
          // Note: this won't work without `new ExtractTextPlugin()` in `plugins`.
        },
        // JSON is not enabled by default in Webpack but both Node and Browserify
        // allow it implicitly so we also enable it.
        {
          test: /\.json$/,
          loader: 'json'
        }
      ]
    },
    
    // We use PostCSS for autoprefixing only.
    postcss: function() {
      return [
        autoprefixer({
          browsers: [
            '>1%',
            'last 4 versions',
            'Firefox ESR',
            'not ie < 9', // React doesn't support IE8 anyway
          ]
        }),
      ];
    },
    plugins: [
      // Makes the public URL available as %PUBLIC_URL% in index.html, e.g.:
      // <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
      // In production, it will be an empty string unless you specify "homepage"
      // in `package.json`, in which case it will be the pathname of that URL.
      new InterpolateHtmlPlugin({
        PUBLIC_URL: publicUrl
      }),
      // Generates an `index.html` file with the <script> injected.
      new HtmlWebpackPlugin({
        inject: true,
        template: paths.appHtml,
        minify: {
          removeComments: true,
          collapseWhitespace: true,
          removeRedundantAttributes: true,
          useShortDoctype: true,
          removeEmptyAttributes: true,
          removeStyleLinkTypeAttributes: true,
          keepClosingSlash: true,
          minifyJS: true,
          minifyCSS: true,
          minifyURLs: true
        }
      }),
      // Makes some environment variables available to the JS code, for example:
      // if (process.env.NODE_ENV === 'production') { ... }. See `./env.js`.
      // It is absolutely essential that NODE_ENV was set to production here.
      // Otherwise React will be compiled in the very slow development mode.
      new webpack.DefinePlugin(env),
      // This helps ensure the builds are consistent if source hasn't changed:
      new webpack.optimize.OccurrenceOrderPlugin(),
      // Try to dedupe duplicated modules, if any:
      new webpack.optimize.DedupePlugin(),
      // Minify the code.
      new webpack.optimize.UglifyJsPlugin({
        compress: {
          screw_ie8: true, // React doesn't support IE8
          warnings: false
        },
        mangle: {
          screw_ie8: true
        },
        output: {
          comments: false,
          screw_ie8: true
        }
      }),
      // Note: this won't work without ExtractTextPlugin.extract(..) in `loaders`.
      new ExtractTextPlugin('static/css/[name].[contenthash:8].css'),
      // 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'
      })
    ],
    // 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: {
      fs: 'empty',
      net: 'empty',
      tls: 'empty'
    }
  };
  