webpack.common.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 = {
   entry: {
      app: './src/app.js',
   },
   output: {
      path: path.join(__dirname, 'public', 'dist'),
      filename: 'bundle.js',
   },
   module: {
      rules: [{
        use: ['babel-loader'],
        test: /\.js$/,
        exclude: /node_modules/
      }, {
        test: /\.s?css$/,
        use: [
          {
            loader: MiniCssExtractPlugin.loader,
            options: {},
          },
          {
            loader: 'css-loader',
            options: {
              sourceMap: true
            }
          },
          {
            loader: 'sass-loader',
            options: {
              sourceMap: true
            }
          }
        ]
      }]
    },
    plugins: [
      new MiniCssExtractPlugin(),
      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),
        'process.env.FIREBASE_APP_ID': JSON.stringify(process.env.FIREBASE_APP_ID),
      })
    ],
 };