This example illustrates a very simple case of Code Splitting with require.ensure.
aandbare required normally via CommonJScis made available(,but doesn't get execute) through therequire.ensurearray.- webpack will load it on demand
banddare required via CommonJs in therequire.ensurecallback- webpack detects that these are in the on-demand-callback and
- will load them on demand
- webpack's optimizer can optimize
baway- as it is already available through the parent chunks
You can see that webpack outputs two files/chunks:
output.jsis the entry chunk and contains- the module system
- chunk loading logic
- the entry point
example.js - module
a - module
b
1.output.jsis an additional chunk (on-demand loaded) and contains- module
c - module
d
- module
You can see that chunks are loaded via JSONP. The additional chunks are pretty small and minimize well.
var a = require("a");
var b = require("b");
require.ensure(["c"], function(require) {
require("b").xyz();
var d = require("d");
});/******/ (() => { // webpackBootstrap
/******/ var __webpack_modules__ = ([
/* 0 */,
/* 1 */
/*!***************************!*\
!*** ./node_modules/a.js ***!
\***************************/
/*! unknown exports (runtime-defined) */
/*! runtime requirements: */
/***/ (() => {
// module a
/***/ }),
/* 2 */
/*!***************************!*\
!*** ./node_modules/b.js ***!
\***************************/
/*! unknown exports (runtime-defined) */
/*! runtime requirements: */
/***/ (() => {
// module b
/***/ })
/******/ ]);/* webpack runtime code */
/************************************************************************/
/******/ // The module cache
/******/ var __webpack_module_cache__ = {};
/******/
/******/ // The require function
/******/ function __webpack_require__(moduleId) {
/******/ // Check if module is in cache
/******/ var cachedModule = __webpack_module_cache__[moduleId];
/******/ if (cachedModule !== undefined) {
/******/ return cachedModule.exports;
/******/ }
/******/ // Create a new module (and put it into the cache)
/******/ var module = __webpack_module_cache__[moduleId] = {
/******/ // no module.id needed
/******/ // no module.loaded needed
/******/ exports: {}
/******/ };
/******/
/******/ // Execute the module function
/******/ __webpack_modules__[moduleId](module, module.exports, __webpack_require__);
/******/
/******/ // Return the exports of the module
/******/ return module.exports;
/******/ }
/******/
/******/ // expose the modules object (__webpack_modules__)
/******/ __webpack_require__.m = __webpack_modules__;
/******/
/************************************************************************/
/******/ /* webpack/runtime/ensure chunk */
/******/ (() => {
/******/ __webpack_require__.f = {};
/******/ // This file contains only the entry chunk.
/******/ // The chunk loading function for additional chunks
/******/ __webpack_require__.e = (chunkId) => {
/******/ return Promise.all(Object.keys(__webpack_require__.f).reduce((promises, key) => {
/******/ __webpack_require__.f[key](chunkId, promises);
/******/ return promises;
/******/ }, []));
/******/ };
/******/ })();
/******/
/******/ /* webpack/runtime/get javascript chunk filename */
/******/ (() => {
/******/ // This function allow to reference async chunks
/******/ __webpack_require__.u = (chunkId) => {
/******/ // return url for filenames based on template
/******/ return "" + chunkId + ".output.js";
/******/ };
/******/ })();
/******/
/******/ /* webpack/runtime/hasOwnProperty shorthand */
/******/ (() => {
/******/ __webpack_require__.o = (obj, prop) => (Object.prototype.hasOwnProperty.call(obj, prop))
/******/ })();
/******/
/******/ /* webpack/runtime/load script */
/******/ (() => {
/******/ var inProgress = {};
/******/ // data-webpack is not used as build has no uniqueName
/******/ // loadScript function to load a script via script tag
/******/ __webpack_require__.l = (url, done, key, chunkId) => {
/******/ if(inProgress[url]) { inProgress[url].push(done); return; }
/******/ var script, needAttach;
/******/ if(key !== undefined) {
/******/ var scripts = document.getElementsByTagName("script");
/******/ for(var i = 0; i < scripts.length; i++) {
/******/ var s = scripts[i];
/******/ if(s.getAttribute("src") == url) { script = s; break; }
/******/ }
/******/ }
/******/ if(!script) {
/******/ needAttach = true;
/******/ script = document.createElement('script');
/******/
/******/ script.charset = 'utf-8';
/******/ script.timeout = 120;
/******/ if (__webpack_require__.nc) {
/******/ script.setAttribute("nonce", __webpack_require__.nc);
/******/ }
/******/
/******/ script.src = url;
/******/ }
/******/ inProgress[url] = [done];
/******/ var onScriptComplete = (prev, event) => {
/******/ // avoid mem leaks in IE.
/******/ script.onerror = script.onload = null;
/******/ clearTimeout(timeout);
/******/ var doneFns = inProgress[url];
/******/ delete inProgress[url];
/******/ script.parentNode && script.parentNode.removeChild(script);
/******/ doneFns && doneFns.forEach((fn) => (fn(event)));
/******/ if(prev) return prev(event);
/******/ }
/******/ ;
/******/ var timeout = setTimeout(onScriptComplete.bind(null, undefined, { type: 'timeout', target: script }), 120000);
/******/ script.onerror = onScriptComplete.bind(null, script.onerror);
/******/ script.onload = onScriptComplete.bind(null, script.onload);
/******/ needAttach && document.head.appendChild(script);
/******/ };
/******/ })();
/******/
/******/ /* webpack/runtime/publicPath */
/******/ (() => {
/******/ __webpack_require__.p = "dist/";
/******/ })();
/******/
/******/ /* webpack/runtime/jsonp chunk loading */
/******/ (() => {
/******/ // no baseURI
/******/
/******/ // object to store loaded and loading chunks
/******/ // undefined = chunk not loaded, null = chunk preloaded/prefetched
/******/ // [resolve, reject, Promise] = chunk loading, 0 = chunk loaded
/******/ var installedChunks = {
/******/ 179: 0
/******/ };
/******/
/******/ __webpack_require__.f.j = (chunkId, promises) => {
/******/ // JSONP chunk loading for javascript
/******/ var installedChunkData = __webpack_require__.o(installedChunks, chunkId) ? installedChunks[chunkId] : undefined;
/******/ if(installedChunkData !== 0) { // 0 means "already installed".
/******/
/******/ // a Promise means "currently loading".
/******/ if(installedChunkData) {
/******/ promises.push(installedChunkData[2]);
/******/ } else {
/******/ if(true) { // all chunks have JS
/******/ // setup Promise in chunk cache
/******/ var promise = new Promise((resolve, reject) => (installedChunkData = installedChunks[chunkId] = [resolve, reject]));
/******/ promises.push(installedChunkData[2] = promise);
/******/
/******/ // start chunk loading
/******/ var url = __webpack_require__.p + __webpack_require__.u(chunkId);
/******/ // create error before stack unwound to get useful stacktrace later
/******/ var error = new Error();
/******/ var loadingEnded = (event) => {
/******/ if(__webpack_require__.o(installedChunks, chunkId)) {
/******/ installedChunkData = installedChunks[chunkId];
/******/ if(installedChunkData !== 0) installedChunks[chunkId] = undefined;
/******/ if(installedChunkData) {
/******/ var errorType = event && (event.type === 'load' ? 'missing' : event.type);
/******/ var realSrc = event && event.target && event.target.src;
/******/ error.message = 'Loading chunk ' + chunkId + ' failed.\n(' + errorType + ': ' + realSrc + ')';
/******/ error.name = 'ChunkLoadError';
/******/ error.type = errorType;
/******/ error.request = realSrc;
/******/ installedChunkData[1](error);
/******/ }
/******/ }
/******/ };
/******/ __webpack_require__.l(url, loadingEnded, "chunk-" + chunkId, chunkId);
/******/ } else installedChunks[chunkId] = 0;
/******/ }
/******/ }
/******/ };
/******/
/******/ // no prefetching
/******/
/******/ // no preloaded
/******/
/******/ // no HMR
/******/
/******/ // no HMR manifest
/******/
/******/ // no on chunks loaded
/******/
/******/ // install a JSONP callback for chunk loading
/******/ var webpackJsonpCallback = (parentChunkLoadingFunction, data) => {
/******/ var [chunkIds, moreModules, runtime] = data;
/******/ // add "moreModules" to the modules object,
/******/ // then flag all "chunkIds" as loaded and fire callback
/******/ var moduleId, chunkId, i = 0;
/******/ if(chunkIds.some((id) => (installedChunks[id] !== 0))) {
/******/ for(moduleId in moreModules) {
/******/ if(__webpack_require__.o(moreModules, moduleId)) {
/******/ __webpack_require__.m[moduleId] = moreModules[moduleId];
/******/ }
/******/ }
/******/ if(runtime) var result = runtime(__webpack_require__);
/******/ }
/******/ if(parentChunkLoadingFunction) parentChunkLoadingFunction(data);
/******/ for(;i < chunkIds.length; i++) {
/******/ chunkId = chunkIds[i];
/******/ if(__webpack_require__.o(installedChunks, chunkId) && installedChunks[chunkId]) {
/******/ installedChunks[chunkId][0]();
/******/ }
/******/ installedChunks[chunkIds[i]] = 0;
/******/ }
/******/
/******/ }
/******/
/******/ var chunkLoadingGlobal = self["webpackChunk"] = self["webpackChunk"] || [];
/******/ chunkLoadingGlobal.forEach(webpackJsonpCallback.bind(null, 0));
/******/ chunkLoadingGlobal.push = webpackJsonpCallback.bind(null, chunkLoadingGlobal.push.bind(chunkLoadingGlobal));
/******/ })();
/******/
/************************************************************************/var __webpack_exports__ = {};
// This entry need to be wrapped in an IIFE because it need to be isolated against other modules in the chunk.
(() => {
/*!********************!*\
!*** ./example.js ***!
\********************/
/*! unknown exports (runtime-defined) */
/*! runtime requirements: __webpack_require__, __webpack_require__.e, __webpack_require__.* */
var a = __webpack_require__(/*! a */ 1);
var b = __webpack_require__(/*! b */ 2);
__webpack_require__.e(/*! require.ensure */ 796).then((function(require) {
__webpack_require__(/*! b */ 2).xyz();
var d = __webpack_require__(/*! d */ 4);
}).bind(null, __webpack_require__)).catch(__webpack_require__.oe);
})();
/******/ })()
;(self["webpackChunk"] = self["webpackChunk"] || []).push([[796],[
/* 0 */,
/* 1 */,
/* 2 */,
/* 3 */
/*!***************************!*\
!*** ./node_modules/c.js ***!
\***************************/
/*! unknown exports (runtime-defined) */
/*! runtime requirements: */
/***/ (() => {
// module c
/***/ }),
/* 4 */
/*!***************************!*\
!*** ./node_modules/d.js ***!
\***************************/
/*! unknown exports (runtime-defined) */
/*! runtime requirements: */
/***/ (() => {
// module d
/***/ })
]]);Minimized
(self.webpackChunk=self.webpackChunk||[]).push([[796],{286:()=>{},882:()=>{}}]);asset output.js 9.49 KiB [emitted] (name: main)
asset 796.output.js 528 bytes [emitted]
chunk (runtime: main) output.js (main) 161 bytes (javascript) 4.98 KiB (runtime) [entry] [rendered]
> ./example.js main
runtime modules 4.98 KiB 6 modules
dependent modules 22 bytes [dependent] 2 modules
./example.js 139 bytes [built] [code generated]
[used exports unknown]
entry ./example.js main
chunk (runtime: main) 796.output.js 22 bytes [rendered]
> ./example.js 3:0-6:2
./node_modules/c.js 11 bytes [built] [code generated]
[used exports unknown]
require.ensure item c ./example.js 3:0-6:2
./node_modules/d.js 11 bytes [built] [code generated]
[used exports unknown]
cjs require d ./example.js 5:12-24
webpack 5.51.1 compiled successfully
asset output.js 1.74 KiB [emitted] [minimized] (name: main)
asset 796.output.js 80 bytes [emitted] [minimized]
chunk (runtime: main) output.js (main) 161 bytes (javascript) 4.98 KiB (runtime) [entry] [rendered]
> ./example.js main
runtime modules 4.98 KiB 6 modules
dependent modules 22 bytes [dependent] 2 modules
./example.js 139 bytes [built] [code generated]
[no exports used]
entry ./example.js main
chunk (runtime: main) 796.output.js 22 bytes [rendered]
> ./example.js 3:0-6:2
./node_modules/c.js 11 bytes [built] [code generated]
[used exports unknown]
require.ensure item c ./example.js 3:0-6:2
./node_modules/d.js 11 bytes [built] [code generated]
[used exports unknown]
cjs require d ./example.js 5:12-24
webpack 5.51.1 compiled successfully