webpack.config.babel.js

import webpack from 'webpack'
import path from 'path'
import HtmlWebpackPlugin from 'html-webpack-plugin'
import autoprefixer from 'autoprefixer'
import ExtractTextPlugin from 'extract-text-webpack-plugin'
import SWPrecacheWebpackPlugin from 'sw-precache-webpack-plugin'
import CopyWebpackPlugin from 'copy-webpack-plugin'
import pkg from './package.json'
import manifest from './app/manifest.json'
import CleanWebpackPlugin from 'clean-webpack-plugin'
import FaviconsWebpackPlugin from 'favicons-webpack-plugin'
import WebpackMd5Hash from 'webpack-md5-hash'
import StatsPlugin from 'stats-webpack-plugin'

const LAUNCH_COMMAND = process.env.npm_lifecycle_event

let SWPrecacheHandleFetch // dynamic variable changed for production and dev

LAUNCH_COMMAND === 'production' ? SWPrecacheHandleFetch = true : SWPrecacheHandleFetch = false

const isProduction = LAUNCH_COMMAND === 'production'
process.env.BABEL_ENV = LAUNCH_COMMAND

const PATHS = {
  root: path.join(__dirname),
  app: path.join(__dirname, 'app'),
  build: path.join(__dirname, 'dist')
}

// inserts link and scripts dependcies in to the generated index.html
const HTMLWebpackPluginConfig = new HtmlWebpackPlugin({
  template: PATHS.app + '/index.html',
  filename: 'index.html',
  inject: 'body'
})

// removed dist directory before run start or run production
const CleanDistPlugin = new CleanWebpackPlugin([PATHS.build], {
  root: PATHS.root,
  verbose: true,
  dry: false
})

// creates favicons and touch icons
const CreateFaviconsPlugin = new FaviconsWebpackPlugin({
   //  source logo
  logo: PATHS.app + '/media/app-logo.png',
  // The prefix for all image files (might be a folder or a name)
  prefix: '/images/icons/',
  // Emit all stats of the generated icons
  emitStats: false,
  // Generate a cache file with control hashes and
  // don't rebuild the favicons until those hashes change
  persistentCache: true,
  // Inject the html into the html-webpack-plugin
  inject: true,
  // favicon background color (see https://github.com/haydenbleasel/favicons#usage)
  background: manifest.background_color,
    // favicon app title (see https://github.com/haydenbleasel/favicons#usage)
  title: pkg.name,

  // which icons should be generated (see https://github.com/haydenbleasel/favicons#usage)
  icons: {
    android: true,
    appleIcon: true,
    appleStartup: false,
    coast: false,
    favicons: true,
    firefox: false,
    opengraph: false,
    twitter: false,
    yandex: false,
    windows: false
  }
})

const DefineProductionENVPlugin = new webpack.DefinePlugin({
  'process.env': {
    NODE_ENV: JSON.stringify('production')
  }
})

const Md5HashPlugin = new WebpackMd5Hash()// required for swprecache hash generation

// copies files at runtime
const CopyFilesPlugin = new CopyWebpackPlugin([
      { from: PATHS.app + '/manifest.json' },
      { from: PATHS.app + '/service-worker-registration.js' }
])

// generates vendor js file (code splitting)
const CommonsChunkPlugin = new webpack.optimize.CommonsChunkPlugin({
  names: ['vendor'],
  minChunks: Infinity
})

// service worker generation
const SWPrecachePlugin = new SWPrecacheWebpackPlugin(
  {
    cacheId: pkg.name, // unique cacheID
    filename: pkg.name + '-service-worker.js', // filename for the generated sw file
    handleFetch: SWPrecacheHandleFetch, // set to false for DEV Server and Change to True for Production
    stripPrefix: 'C:/Users/dist/',
    navigateFallback: '/index.html',
    navigateFallbackWhitelist: [/^\/auth|logout|eventsFeed|prizesFeed|eventPreview|addEvent|addPrize|howItWorks|confirmEvent|app|manifest|service-worker-registration|style|vendor\//],
    runtimeCaching: [{
      // web fonts
      urlPattern: /^https:\/\/fonts.googleapis.com\/.*/,
      handler: 'cacheFirst'
    }, {
      // firebase storage images
      urlPattern: /^https:\/\/fonts.gstatic.com\/.*/,
      handler: 'cacheFirst'
    }, {
      // firebase storage images
      urlPattern: /^https:\/\/firebasestorage.googleapis.com\/.*/,
      handler: 'cacheFirst'
    }, {
      // google Map Images images
      urlPattern: /^https:\/\/maps.googleapis.com\/maps\/api\/.*/,
      handler: 'cacheFirst'
    }]
  }
)

// minifies all build code
const UglifyJsPlugin = new webpack.optimize.UglifyJsPlugin({
  compressor: {
    warnings: false
  }
})

const ExtractCSSPlugin = new ExtractTextPlugin('/[name].css') // extracts seperate css file for caching instead of inline styles

const WebpackStatsPlugin = new StatsPlugin('../Stats.json', {
  chunkModules: true,
  exclude: [/node_modules[\\\/]react/]
})

const DedupePlugin = new webpack.optimize.DedupePlugin() // deduplicates equal or similar files

const base = {
  entry: {
    app: [
      'babel-polyfill',
      PATHS.app
    ],
    vendor: ['react', 'react-dom', 'react-router', 'redux', 'react-redux']
  },
  postcss: [ autoprefixer({ browsers: ['last 2 versions'] }) ],
  resolve: {
    root: path.resolve('./app')
  }
}

const developmentConfig = {
  devtool: 'cheap-module-inline-source-map',
  output: {
    path: PATHS.build,
    filename: '/[name].js'
  },
  module: {
    loaders: [
      {test: /\.js$/, exclude: /node_modules/, loader: 'babel-loader'},
      {test: /\.style.js$/, loader: 'style!css!postcss?parser=postcss-js!babel'},
      {test: /\.css$/, loader: 'style!css?sourceMap&modules&localIdentName=[name]__[local]___[hash:base64:5]&importLoader=1!postcss'},
      {test: /\.scss$/, loader: 'style!css?sourceMap&modules&localIdentName=[name]__[local]___[hash:base64:5]&postcss!sass'}
    ]
  },
  devServer: {
    contentBase: PATHS.build,
    historyApiFallback: true,
    hot: true,
    inline: true,
    progress: true
  },
  plugins: [HTMLWebpackPluginConfig, new webpack.HotModuleReplacementPlugin(), CleanDistPlugin, CommonsChunkPlugin, CopyFilesPlugin, CreateFaviconsPlugin]
}

const productionConfig = {
  devtool: 'cheap-module-source-map',
  output: {
    path: PATHS.build,
    filename: '/[name].[chunkhash].js',
    // This is used for require.ensure. The setup
    // will work without but this is useful to set.
    chunkFilename: '/[chunkhash].js'
  },
  recordsPath: path.resolve(__dirname, PATHS.root + '/webpack-records.json'), // needed so the vendor js doesnt change hash when not changed only app.js changes
  module: {
    loaders: [
      {test: /\.js$/, exclude: /node_modules/, loader: 'babel-loader'},
      { test: /\.css$/, loader: ExtractTextPlugin.extract('style', 'css?sourceMap&modules&localIdentName=[name]__[local]___[hash:base64:5]&importLoader=1!postcss') },
      { test: /\.scss$/, loader: ExtractTextPlugin.extract('style', 'css?sourceMap&modules&localIdentName=[name]__[local]___[hash:base64:5]&importLoader=1!postcss!sass') }
    ]
  },
  plugins: [HTMLWebpackPluginConfig, DefineProductionENVPlugin, CleanDistPlugin, Md5HashPlugin, CopyFilesPlugin, CommonsChunkPlugin, SWPrecachePlugin, DedupePlugin, UglifyJsPlugin, ExtractCSSPlugin, WebpackStatsPlugin, CreateFaviconsPlugin]
}
export default Object.assign({}, base, isProduction === true ? productionConfig : developmentConfig)

Just curious, how does this config work without a module.exports =?