webpack.config.js

const isDev = process.env.NODE_ENV === 'development'
const MiniCssExtractPlugin = require('mini-css-extract-plugin')

module.exports = {
  mode: isDev ? 'development' : 'production',
  entry: [
    '@babel/polyfill', // enables async-await
    './client/index.js'
  ],
  output: {
    path: __dirname,
    filename: './public/bundle.js'
  },
  resolve: {
    extensions: ['.js', '.jsx']
  },
  devtool: 'source-map',
  module: {
    rules: [
      {
        test: /\.jsx?$/,
        exclude: /node_modules/,
        loader: 'babel-loader'
      },
      {
        test: /\.scss$/,
        use: [
          process.env.NODE_ENV !== 'production'
            ? 'style-loader'
            : MiniCssExtractPlugin.loader,
          'css-loader', // translates CSS into CommonJS
          'sass-loader' // compiles Sass to CSS, using Node Sass by default
        ]
      }
    ]
  },
  plugins: [
    new MiniCssExtractPlugin({
      // Options similar to the same options in webpackOptions.output
      // both options are optional
      filename: './public/styles/main.css',
      chunkFilename: './public/styles/[id].css'
    })
  ]
}