old_contents: // @ts-check
  
  const path = require('path');
  const MiniCssExtractPlugin = require('mini-css-extract-plugin');
  
  module.exports = {
    entry: {
      App: ['babel-polyfill', './App.jsx']
    },
  
    output: {
      path: path.join(__dirname, 'build'),
      filename: '[name].js'
    },
  
    plugins: [
      new MiniCssExtractPlugin({filename: '[name].css'})
    ],
  
    resolve: {
      extensions: ['.js', '.jsx']
    },
  
    module: {
      rules: [
        {
          test: /\.jsx?$/,
          exclude: /node_modules/,
          loader: 'babel-loader',
          options: {
            presets: ['env', 'react'],
            plugins: [require('babel-plugin-transform-class-properties')]
          }
        },
        { test: /\.js$/, loader: 'source-map-loader' },
        { test: /\.(html|css|png)$/, loader: 'file-loader', options: {name: '[path][name].[ext]'} },
        {
          // FIXME Don't know how to make source maps work
          // See SourceMap not working with Webpack 4.8.1 https://github.com/webpack-contrib/mini-css-extract-plugin/issues/141
          test: /\.scss$/,
          use: [
            MiniCssExtractPlugin.loader,
            { loader: 'css-loader', options: {sourceMap: true} },
            { loader: 'sass-loader', options: {sourceMap: true} }
          ]
        }
      ]
    }
  };
  
new_contents: // @ts-check
  
  const path = require('path');
  const MiniCssExtractPlugin = require('mini-css-extract-plugin');
  
  module.exports = {
    entry: {
      App: './App.jsx'
    },
  
    output: {
      path: path.join(__dirname, 'build'),
      filename: '[name].js'
    },
  
    plugins: [
      new MiniCssExtractPlugin({filename: '[name].css'})
    ],
  
    resolve: {
      extensions: ['.js', '.jsx']
    },
  
    module: {
      rules: [
        {
          test: /\.jsx?$/,
          exclude: /node_modules/,
          loader: 'babel-loader',
          options: {
            presets: [
              ['env', {
                targets: {
                  browsers: ['> 1%', 'IE >= 10']
                },
                useBuiltIns: true,
                debug: true
              }],
              'react',
            ],
            plugins: [require('babel-plugin-transform-class-properties')]
          }
        },
        { test: /\.js$/, loader: 'source-map-loader' },
        { test: /\.(html|css|png)$/, loader: 'file-loader', options: {name: '[path][name].[ext]'} },
        {
          // FIXME Don't know how to make source maps work
          // See SourceMap not working with Webpack 4.8.1 https://github.com/webpack-contrib/mini-css-extract-plugin/issues/141
          test: /\.scss$/,
          use: [
            MiniCssExtractPlugin.loader,
            { loader: 'css-loader', options: {sourceMap: true} },
            { loader: 'sass-loader', options: {sourceMap: true} }
          ]
        }
      ]
    }
  };
  
subject: Fix Bootstrap4 example polyfills