webpack.config.js

const isDev = process.env.NODE_ENV === 'development';

module.exports = {
  mode: isDev ? 'development' : 'production',
  entry: [
    '@babel/polyfill', // enables async-await
    './client/index.js',
  ],
  mode: 'development',
  output: {
    path: __dirname, // assumes your bundle.js will also be in the root of your project folder
    filename: './public/bundle.js',
  },
  devtool: 'source-maps',
  module: {
    rules: [
      {
        test: /\.jsx?$/,
        exclude: /(node_modules|bower_components)/,
        loader: 'babel-loader',
        options: {
          presets: [
            ['@babel/preset-env', { useBuiltIns: 'entry', corejs: '^2.0' }],
          ],
        },
      },
      // use the style-loader/css-loader combos for anything matching the .css extension
      {
        test: /\.css$/,
        use: ['style-loader', 'css-loader'],
      },
    ],
  },
};