Application bootstrap by Webpack build type

bundle.js

/******/ (function(modules) { // webpackBootstrap
/******/ 	// The module cache
/******/ 	var installedModules = {};

/******/ 	// The require function
/******/ 	function __webpack_require__(moduleId) {

/******/ 		// Check if module is in cache
/******/ 		if(installedModules[moduleId])
/******/ 			return installedModules[moduleId].exports;

/******/ 		// Create a new module (and put it into the cache)
/******/ 		var module = installedModules[moduleId] = {
/******/ 			exports: {},
/******/ 			id: moduleId,
/******/ 			loaded: false
/******/ 		};

/******/ 		// Execute the module function
/******/ 		modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);

/******/ 		// Flag the module as loaded
/******/ 		module.loaded = true;

/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}


/******/ 	// expose the modules object (__webpack_modules__)
/******/ 	__webpack_require__.m = modules;

/******/ 	// expose the module cache
/******/ 	__webpack_require__.c = installedModules;

/******/ 	// __webpack_public_path__
/******/ 	__webpack_require__.p = "";

/******/ 	// Load entry module and return exports
/******/ 	return __webpack_require__(0);
/******/ })
/************************************************************************/
/******/ ([
/* 0 */
/***/ function(module, exports, __webpack_require__) {

	const config = __webpack_require__(1);

	console.dir(config);

/***/ },
/* 1 */
/***/ function(module, exports) {

	module.exports = {dev: true};

/***/ }
/******/ ]);

bundle.prod.js

/******/ (function(modules) { // webpackBootstrap
/******/ 	// The module cache
/******/ 	var installedModules = {};

/******/ 	// The require function
/******/ 	function __webpack_require__(moduleId) {

/******/ 		// Check if module is in cache
/******/ 		if(installedModules[moduleId])
/******/ 			return installedModules[moduleId].exports;

/******/ 		// Create a new module (and put it into the cache)
/******/ 		var module = installedModules[moduleId] = {
/******/ 			exports: {},
/******/ 			id: moduleId,
/******/ 			loaded: false
/******/ 		};

/******/ 		// Execute the module function
/******/ 		modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);

/******/ 		// Flag the module as loaded
/******/ 		module.loaded = true;

/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}


/******/ 	// expose the modules object (__webpack_modules__)
/******/ 	__webpack_require__.m = modules;

/******/ 	// expose the module cache
/******/ 	__webpack_require__.c = installedModules;

/******/ 	// __webpack_public_path__
/******/ 	__webpack_require__.p = "";

/******/ 	// Load entry module and return exports
/******/ 	return __webpack_require__(0);
/******/ })
/************************************************************************/
/******/ ([
/* 0 */
/***/ function(module, exports, __webpack_require__) {

	const config = __webpack_require__(1);

	console.dir(config);

/***/ },
/* 1 */
/***/ function(module, exports) {

	module.exports = {prod: true}

/***/ }
/******/ ]);

config-dev.js

module.exports = {dev: true};

config.js

module.exports = {prod: true}

index.js

const config = require('./config' + (__DEV__ ? '-dev' : ''));

console.dir(config);

webpack.config.js

const webpack = require('webpack');
const build = process.env.BUILD && process.env.BUILD.trim();
const isProduction = build === 'production';

const definePlugin = new webpack.DefinePlugin({
  __DEV__: !isProduction
});

module.exports = {
  entry: './index.js',
  output: {
    filename: isProduction ? 'bundle.prod.js' : 'bundle.js'
  },
  plugins: [definePlugin]
};

Using the technique with bootstrapping the application's module tree is quite differen from setting a global config. The latter would inline the mocked config, like in the example below.

// webpack.config.js
const definePlugin = new webpack.DefinePlugin({
  __DEV__: !isProduction,
  globalConfig: !isProduction ? JSON.stringify({ in: 'dev' }) : JSON.stringify({ in: 'prod' }) 
});

// index.js
console.dir(config);
console.log(globalConfig);

// bundle.js
/* 0 */
/***/ function(module, exports, __webpack_require__) {

    const config = __webpack_require__(1);

    console.dir(config);
    console.log(({"in":"dev"}));

/***/ }

// bundle.prod.js
/* 0 */
/***/ function(module, exports, __webpack_require__) {

    const config = __webpack_require__(1);

    console.dir(config);
    console.log(({"in":"prod"}));

/***/ }

Repo for further development:
https://github.com/jouni-kantola/webpack-output-by-build-type