webpack/examples/code-splitting

This example illustrates a very simple case of Code Splitting with require.ensure.

• a and b are required normally via CommonJS
• c is depended through the require.ensure array.
  • This means: make it available, but don't execute it
  • webpack will load it on demand
• b and d are required via CommonJs in the require.ensure callback
  • webpack detects that these are in the on-demand-callback and
  • will load them on demand
  • webpacks optimizer can optimize b away
    • as it is already available through the parent chunks

You can see that webpack outputs two files/chunks:

• output.js is the entry chunk and contains
  • the module system
  • chunk loading logic
  • the entry point example.js
  • module a
  • module b
• 1.js is an additional chunk (on demand loaded) and contains
  • module c
  • module d

You can see that chunks are loaded via JSONP. The additional chunks are pretty small and minimize well.

example.js

var a = require("a");
var b = require("b");
require.ensure(["c"], function(require) {
    require("b").xyz();
    var d = require("d");
});

js/output.js

/******/ (function(modules) { /* webpackBootstrap */ })

/******/ (function(modules) { // webpackBootstrap
/******/ 	// install a JSONP callback for chunk loading
/******/ 	var parentJsonpFunction = window["webpackJsonp"];
/******/ 	window["webpackJsonp"] = function webpackJsonpCallback(chunkIds, moreModules, executeModules) {
/******/ 		// add "moreModules" to the modules object,
/******/ 		// then flag all "chunkIds" as loaded and fire callback
/******/ 		var moduleId, chunkId, i = 0, resolves = [], result;
/******/ 		for(;i < chunkIds.length; i++) {
/******/ 			chunkId = chunkIds[i];
/******/ 			if(installedChunks[chunkId]) {
/******/ 				resolves.push(installedChunks[chunkId][0]);
/******/ 			}
/******/ 			installedChunks[chunkId] = 0;
/******/ 		}
/******/ 		for(moduleId in moreModules) {
/******/ 			if(Object.prototype.hasOwnProperty.call(moreModules, moduleId)) {
/******/ 				modules[moduleId] = moreModules[moduleId];
/******/ 			}
/******/ 		}
/******/ 		if(parentJsonpFunction) parentJsonpFunction(chunkIds, moreModules, executeModules);
/******/ 		while(resolves.length) {
/******/ 			resolves.shift()();
/******/ 		}
/******/
/******/ 	};
/******/
/******/ 	// The module cache
/******/ 	var installedModules = {};
/******/
/******/ 	// objects to store loaded and loading chunks
/******/ 	var installedChunks = {
/******/ 		1: 0
/******/ 	};
/******/
/******/ 	var resolvedPromise = new Promise(function(resolve) { resolve(); });
/******/
/******/ 	// 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] = {
/******/ 			i: moduleId,
/******/ 			l: false,
/******/ 			exports: {}
/******/ 		};
/******/
/******/ 		// Execute the module function
/******/ 		modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
/******/
/******/ 		// Flag the module as loaded
/******/ 		module.l = true;
/******/
/******/ 		// Return the exports of the module
/******/ 		return module.exports;
/******/ 	}
/******/
/******/ 	// This file contains only the entry chunk.
/******/ 	// The chunk loading function for additional chunks
/******/ 	__webpack_require__.e = function requireEnsure(chunkId) {
/******/ 		if(installedChunks[chunkId] === 0) {
/******/ 			return resolvedPromise;
/******/ 		}
/******/
/******/ 		// a Promise means "currently loading".
/******/ 		if(installedChunks[chunkId]) {
/******/ 			return installedChunks[chunkId][2];
/******/ 		}
/******/
/******/ 		// setup Promise in chunk cache
/******/ 		var promise = new Promise(function(resolve, reject) {
/******/ 			installedChunks[chunkId] = [resolve, reject];
/******/ 		});
/******/ 		installedChunks[chunkId][2] = promise;
/******/
/******/ 		// start chunk loading
/******/ 		var head = document.getElementsByTagName('head')[0];
/******/ 		var script = document.createElement('script');
/******/ 		script.type = 'text/javascript';
/******/ 		script.charset = 'utf-8';
/******/ 		script.async = true;
/******/ 		script.timeout = 120000;
/******/
/******/ 		if (__webpack_require__.nc) {
/******/ 			script.setAttribute("nonce", __webpack_require__.nc);
/******/ 		}
/******/ 		script.src = __webpack_require__.p + "" + chunkId + ".output.js";
/******/ 		var timeout = setTimeout(onScriptComplete, 120000);
/******/ 		script.onerror = script.onload = onScriptComplete;
/******/ 		function onScriptComplete() {
/******/ 			// avoid mem leaks in IE.
/******/ 			script.onerror = script.onload = null;
/******/ 			clearTimeout(timeout);
/******/ 			var chunk = installedChunks[chunkId];
/******/ 			if(chunk !== 0) {
/******/ 				if(chunk) {
/******/ 					chunk[1](new Error('Loading chunk ' + chunkId + ' failed.'));
/******/ 				}
/******/ 				installedChunks[chunkId] = undefined;
/******/ 			}
/******/ 		};
/******/ 		head.appendChild(script);
/******/
/******/ 		return promise;
/******/ 	};
/******/
/******/ 	// expose the modules object (__webpack_modules__)
/******/ 	__webpack_require__.m = modules;
/******/
/******/ 	// expose the module cache
/******/ 	__webpack_require__.c = installedModules;
/******/
/******/ 	// identity function for calling harmony imports with the correct context
/******/ 	__webpack_require__.i = function(value) { return value; };
/******/
/******/ 	// define getter function for harmony exports
/******/ 	__webpack_require__.d = function(exports, name, getter) {
/******/ 		if(!__webpack_require__.o(exports, name)) {
/******/ 			Object.defineProperty(exports, name, {
/******/ 				configurable: false,
/******/ 				enumerable: true,
/******/ 				get: getter
/******/ 			});
/******/ 		}
/******/ 	};
/******/
/******/ 	// getDefaultExport function for compatibility with non-harmony modules
/******/ 	__webpack_require__.n = function(module) {
/******/ 		var getter = module && module.__esModule ?
/******/ 			function getDefault() { return module['default']; } :
/******/ 			function getModuleExports() { return module; };
/******/ 		__webpack_require__.d(getter, 'a', getter);
/******/ 		return getter;
/******/ 	};
/******/
/******/ 	// Object.prototype.hasOwnProperty.call
/******/ 	__webpack_require__.o = function(object, property) { return Object.prototype.hasOwnProperty.call(object, property); };
/******/
/******/ 	// __webpack_public_path__
/******/ 	__webpack_require__.p = "js/";
/******/
/******/ 	// on error function for async loading
/******/ 	__webpack_require__.oe = function(err) { console.error(err); throw err; };
/******/
/******/ 	// Load entry module and return exports
/******/ 	return __webpack_require__(__webpack_require__.s = 2);
/******/ })
/************************************************************************/

/******/ ([
/* 0 */
/* unknown exports provided */
/* all exports used */
/*!****************!*\
  !*** ./~/b.js ***!
  \****************/
/***/ (function(module, exports) {

// module b

/***/ }),
/* 1 */
/* unknown exports provided */
/* all exports used */
/*!****************!*\
  !*** ./~/a.js ***!
  \****************/
/***/ (function(module, exports) {

// module a

/***/ }),
/* 2 */
/* unknown exports provided */
/* all exports used */
/*!********************!*\
  !*** ./example.js ***!
  \********************/
/***/ (function(module, exports, __webpack_require__) {

var a = __webpack_require__(/*! a */ 1);
var b = __webpack_require__(/*! b */ 0);
__webpack_require__.e/* require.ensure */(0).then((function(require) {
    __webpack_require__(/*! b */ 0).xyz();
    var d = __webpack_require__(/*! d */ 4);
}).bind(null, __webpack_require__)).catch(__webpack_require__.oe);

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

js/0.output.js

webpackJsonp([0],[
/* 0 */,
/* 1 */,
/* 2 */,
/* 3 */
/* unknown exports provided */
/* all exports used */
/*!****************!*\
  !*** ./~/c.js ***!
  \****************/
/***/ (function(module, exports) {

// module c

/***/ }),
/* 4 */
/* unknown exports provided */
/* all exports used */
/*!****************!*\
  !*** ./~/d.js ***!
  \****************/
/***/ (function(module, exports) {

// module d

/***/ })
]);

Minimized

webpackJsonp([0],[,,,function(n,c){},function(n,c){}]);

Info

Uncompressed

Hash: 2426d9b9f5a83189d95d
Version: webpack 2.6.0
      Asset       Size  Chunks             Chunk Names
0.output.js  420 bytes       0  [emitted]  
  output.js    6.75 kB       1  [emitted]  main
Entrypoint main = output.js
chunk    {0} 0.output.js 22 bytes {1} [rendered]
    > [2] ./example.js 3:0-6:2
    [3] ./~/c.js 11 bytes {0} [built]
        require.ensure item c [2] ./example.js 3:0-6:2
    [4] ./~/d.js 11 bytes {0} [built]
        cjs require d [2] ./example.js 5:12-24
chunk    {1} output.js (main) 166 bytes [entry] [rendered]
    > main [2] ./example.js 
    [0] ./~/b.js 11 bytes {1} [built]
        cjs require b [2] ./example.js 2:8-20
        cjs require b [2] ./example.js 4:4-16
    [1] ./~/a.js 11 bytes {1} [built]
        cjs require a [2] ./example.js 1:8-20
    [2] ./example.js 144 bytes {1} [built]

Minimized (uglify-js, no zip)

Hash: 2426d9b9f5a83189d95d
Version: webpack 2.6.0
      Asset      Size  Chunks             Chunk Names
0.output.js  55 bytes       0  [emitted]  
  output.js   1.48 kB       1  [emitted]  main
Entrypoint main = output.js
chunk    {0} 0.output.js 22 bytes {1} [rendered]
    > [2] ./example.js 3:0-6:2
    [3] ./~/c.js 11 bytes {0} [built]
        require.ensure item c [2] ./example.js 3:0-6:2
    [4] ./~/d.js 11 bytes {0} [built]
        cjs require d [2] ./example.js 5:12-24
chunk    {1} output.js (main) 166 bytes [entry] [rendered]
    > main [2] ./example.js 
    [0] ./~/b.js 11 bytes {1} [built]
        cjs require b [2] ./example.js 2:8-20
        cjs require b [2] ./example.js 4:4-16
    [1] ./~/a.js 11 bytes {1} [built]
        cjs require a [2] ./example.js 1:8-20
    [2] ./example.js 144 bytes {1} [built]