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' }); // eslint-disable-line global-require
} else if (process.env.NODE_ENV === 'development') {
  require('dotenv').config({ path: '.env.development' }); // eslint-disable-line global-require
}

module.exports = env => {
  const isProduction = env === 'production';

  return {
    entry: ['@babel/polyfill', './src/app.js'],
    output: {
      path: path.join(__dirname, 'public', 'dist'),
      filename: 'bundle.js'
    },
    mode: 'development',
    module: {
      rules: [
        {
          loader: 'babel-loader',
          test: /\.js$/,
          exclude: /node_modules/
        },
        {
          test: /\.s?css$/,
          use: [
            MiniCssExtractPlugin.loader,
            {
              loader: 'css-loader',
              options: {
                sourceMap: true
              }
            },
            {
              loader: 'sass-loader',
              options: {
                sourceMap: true
              }
            }
          ]
        }
      ]
    },
    plugins: [
      new MiniCssExtractPlugin({
        filename: 'styles.css'
      }),
      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/'
    }
  };
};