Webpack config to support environment variables in JS app

some_js_file.js

var domain = process.env.DOMAIN || null;
console.log(domain);

webpack.config.js

var ExtractTextPlugin = require("extract-text-webpack-plugin"),
    webpack = require('webpack');

module.exports = {
  node: {
    fs: "empty"
  },
  entry: './index',
  output: {
    path: __dirname,
    filename: 'bundle.js'
  },
  module: {
    loaders: [
      {
        test: /\.css$/,
        loader: ExtractTextPlugin.extract('style-loader', 'css-loader')
      },
      {
        test: /.js?$/,
        loader: 'babel-loader',
        exclude: /node_modules/,
        query: {
          presets: ['es2015', 'react']
        }
      }
    ]
  },
  plugins: [
		new ExtractTextPlugin('bundle.css'),
    new webpack.DefinePlugin({
      'process.env': {
        'DOMAIN': JSON.stringify(process.env.DOMAIN)
      }
    })
	],
  devServer: {
    port: 8080,
    historyApiFallback: true
  }
}