webpack.config.js

const path = require('path');
const webpack=require('webpack');
const ExtractTextPlugin = require('extract-text-webpack-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 ExtractTextPlugin('styles.css');

  return {
    entry: ['babel-polyfill','./src/app.js'],
    output: {
      path: path.join(__dirname, 'public','dist'),
      filename: 'bundle.js'
    },
    module: {
      rules: [{
        loader: 'babel-loader',
        test: /\.js$/,
        exclude: /node_modules/
      }, {
        test: /\.s?css$/,
        use: CSSExtract.extract({
          use: [
            {
              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),
          'process.env.FIREBASE_APP_ID':JSON.stringify(process.env.FIREBASE_APP_ID)
      })
    ],
    devtool: isProduction ? 'source-map' : 'inline-source-map',
    devServer: {
      contentBase: path.join(__dirname, 'public'),
      historyApiFallback: true,
      publicPath:'/dist/'
    }
  };
};