webpack.config.js

const path = require('path')
const webpack = require('webpack')
const MiniCssExtractPlugin = require('mini-css-extract-plugin')

process.env.NODE_ENV = process.env.NODE_ENV || 'development'

if (process.env.NODE_ENV === 'test') {
  require('dotenv').config({ path: '.env.test' })
} else if (process.env.NODE_ENV === 'development') {
  require('dotenv').config({ path: '.env.development' })
}

module.exports = (env) => {
  const isProduction = env === 'production'
  const CSSExtract = new MiniCssExtractPlugin({filename: 'styles.css'})

  return {
    mode: 'development',
    entry: ['babel-polyfill', './src/app.js'],
    output: {
      path: path.join(__dirname, 'public', 'dist'),
      filename: 'bundle.js'
    },
    module: {
      rules: [{
        test: /\.js$/,
        loader: 'babel-loader',
        exclude: /node_modules/
      }, {
        test: /\.s?css$/,
        use: [
          isProduction ? MiniCssExtractPlugin.loader : 'style-loader',
          {
            loader: 'css-loader',
            options: {
              sourceMap: true
            }
          },
          {
            loader: 'sass-loader',
            options: {
              sourceMap: true
            }
          }
        ]
      }]
    },
    plugins: [
      CSSExtract,
      new webpack.DefinePlugin({
        'process.env.FIREBASE_API_KEY': JSON.stringify(process.env.FIREBASE_API_KEY),
        'process.env.FIREBASE_AUTH_DOMAIN': JSON.stringify(process.env.FIREBASE_AUTH_DOMAIN),
        'process.env.FIREBASE_DATABASE_URL': JSON.stringify(process.env.FIREBASE_DATABASE_URL),
        'process.env.FIREBASE_PROJECT_ID': JSON.stringify(process.env.FIREBASE_PROJECT_ID),
        'process.env.FIREBASE_STORAGE_BUCKET': JSON.stringify(process.env.FIREBASE_STORAGE_BUCKET),
        'process.env.FIREBASE_MESSAGING_SENDER_ID': JSON.stringify(process.env.FIREBASE_MESSAGING_SENDER_ID)
      })
    ],
    devtool: isProduction ? 'source-map' : 'inline-source-map',
    devServer: {
      contentBase: path.join(__dirname, 'public'),
      historyApiFallback: true,
      publicPath: '/dist/'
    }
  }
}