webpack动态import原理是什么
今天小编给大家分享一下webpack动态import原理是什么的相关知识点,内容详细,逻辑清晰,相信大部分人都还太了解这方面的知识,所以分享这篇文章给大家参考一下,希望大家阅读完这篇文章后有所收获,下面我们一起来了解一下吧。
例子
// index.jsimport('./test').then(fn => { console.log(fn.default());})
// test.jsexport default function func() { return 1}
打包后的代码包含两个文件 bundle.js 和 0.js
点击展开bundle.js
(function(modules) { // webpackBootstrap // install a JSONP callback for chunk loading function webpackJsonpCallback(data) { var chunkIds = data[0]; var moreModules = data[1]; // add "moreModules" to the modules object, // then flag all "chunkIds" as loaded and fire callback var moduleId, chunkId, i = 0, resolves = []; for(;i < chunkIds.length; i++) { chunkId = chunkIds[i]; if(Object.prototype.hasOwnProperty.call(installedChunks, chunkId) && 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(data); while(resolves.length) { resolves.shift()(); } }; // The module cache var installedModules = {}; // object to store loaded and loading chunks // undefined = chunk not loaded, null = chunk preloaded/prefetched // Promise = chunk loading, 0 = chunk loaded var installedChunks = { "main": 0 }; // script path function function jsonpScriptclass="lazy" data-src(chunkId) { return __webpack_require__.p + "" + chunkId + ".bundle.js" } // 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) { var promises = []; // JSONP chunk loading for javascript var installedChunkData = installedChunks[chunkId]; if(installedChunkData !== 0) { // 0 means "already installed". // a Promise means "currently loading". if(installedChunkData) { promises.push(installedChunkData[2]); } else { // setup Promise in chunk cache var promise = new Promise(function(resolve, reject) { installedChunkData = installedChunks[chunkId] = [resolve, reject]; }); promises.push(installedChunkData[2] = promise); // start chunk loading var script = document.createElement('script'); var onScriptComplete; script.charset = 'utf-8'; script.timeout = 120; if (__webpack_require__.nc) { script.setAttribute("nonce", __webpack_require__.nc); } script.class="lazy" data-src = jsonpScriptclass="lazy" data-src(chunkId); // create error before stack unwound to get useful stacktrace later var error = new Error(); onScriptComplete = function (event) { // avoid mem leaks in IE. script.onerror = script.onload = null; clearTimeout(timeout); var chunk = installedChunks[chunkId]; if(chunk !== 0) { if(chunk) { var errorType = event && (event.type === 'load' ? 'missing' : event.type); var realclass="lazy" data-src = event && event.target && event.target.class="lazy" data-src; error.message = 'Loading chunk ' + chunkId + ' failed.\n(' + errorType + ': ' + realclass="lazy" data-src + ')'; error.name = 'ChunkLoadError'; error.type = errorType; error.request = realclass="lazy" data-src; chunk[1](error); } installedChunks[chunkId] = undefined; } }; var timeout = setTimeout(function(){ onScriptComplete({ type: 'timeout', target: script }); }, 120000); script.onerror = script.onload = onScriptComplete; document.head.appendChild(script); } } return Promise.all(promises); }; // expose the modules object (__webpack_modules__) __webpack_require__.m = modules; // expose the module cache __webpack_require__.c = installedModules; // define getter function for harmony exports __webpack_require__.d = function(exports, name, getter) { if(!__webpack_require__.o(exports, name)) { Object.defineProperty(exports, name, { enumerable: true, get: getter }); } }; // define __esModule on exports __webpack_require__.r = function(exports) { if(typeof Symbol !== 'undefined' && Symbol.toStringTag) { Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' }); } Object.defineProperty(exports, '__esModule', { value: true }); }; // create a fake namespace object // mode & 1: value is a module id, require it // mode & 2: merge all properties of value into the ns // mode & 4: return value when already ns object // mode & 8|1: behave like require __webpack_require__.t = function(value, mode) { if(mode & 1) value = __webpack_require__(value); if(mode & 8) return value; if((mode & 4) && typeof value === 'object' && value && value.__esModule) return value; var ns = Object.create(null); __webpack_require__.r(ns); Object.defineProperty(ns, 'default', { enumerable: true, value: value }); if(mode & 2 && typeof value != 'string') for(var key in value) __webpack_require__.d(ns, key, function(key) { return value[key]; }.bind(null, key)); return ns; }; // 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 = ""; // on error function for async loading __webpack_require__.oe = function(err) { console.error(err); throw err; }; var jsonpArray = window["webpackJsonp"] = window["webpackJsonp"] || []; var oldJsonpFunction = jsonpArray.push.bind(jsonpArray); jsonpArray.push = webpackJsonpCallback; jsonpArray = jsonpArray.slice(); for(var i = 0; i < jsonpArray.length; i++) webpackJsonpCallback(jsonpArray[i]); var parentJsonpFunction = oldJsonpFunction; // Load entry module and return exports return __webpack_require__(__webpack_require__.s = "./class="lazy" data-src/index.js"); }) ({ "./class="lazy" data-src/index.js": (function(module, exports, __webpack_require__) {eval("__webpack_require__.e( 0).then(__webpack_require__.bind(null, \"./class="lazy" data-src/test.js\")).then(function (fn) {\n console.log(fn[\"default\"]());\n});\n\n//# sourceURL=webpack:///./class="lazy" data-src/index.js?"); }) });
点击展开0.js
(window["webpackJsonp"] = window["webpackJsonp"] || []).push([[0],{ "./class="lazy" data-src/test.js": (function(module, __webpack_exports__, __webpack_require__) {"use strict";eval("__webpack_require__.r(__webpack_exports__);\n __webpack_require__.d(__webpack_exports__, \"default\", function() { return func; });\nfunction func() {\n return 1;\n}\n\n//# sourceURL=webpack:///./class="lazy" data-src/test.js?"); })}]);
1. 模块加载
webpack通过__webpack_require__加载模块代码
// bundle.jsfunction __webpack_require__(moduleId) // 如果模块已经加载,直接返回模块导出if(installedModules[moduleId]) {return installedModules[moduleId].exports;} // 模块导出和模块信息var module = installedModules[moduleId] = {i: moduleId,l: false,exports: {}} // 执行模块代码modules[moduleId].call(module.exports, module, module.exports, __webpack_require__)module.l = true // 标记模块已经加载完成return module.exports;}
__webpack_require__('index.js')
然后执行index.js编译后的代码,如下。
Promise.all( [ __webpack_require__.e(0) ]).then( __webpack_require__.bind(null, "./class="lazy" data-src/test.js")).then(function (fn) { console.log(fn.default());}));
2. jsonp动态加载script
先一步步来,看下__webpack_require__.e这个方法,它是最先调用的。
// bundle.js__webpack_require__.e = function requireEnsure(chunkId) {var promises = []var installedChunkData = installedChunks[chunkId]; // 如果这个chunk已经加载过了 就不需要加载了if(installedChunkData !== 0) { // 0 means "already installed"if(installedChunkData) {promises.push(installedChunkData[2]);} else { // 为这个chunk创建一个promisevar promise = new Promise(function(resolve, reject) { // 记录这个chunk对应promise的resolve和reject方法installedChunkData = installedChunks[chunkId] = [resolve, reject];}); // promises数组里添加这个chunk对应的promisepromises.push(installedChunkData[2] = promise) // ============== 动态创建script =================var script = document.createElement('script');var onScriptCompletescript.charset = 'utf-8';script.timeout = 120;if (__webpack_require__.nc) {script.setAttribute("nonce", __webpack_require__.nc);}script.class="lazy" data-src = jsonpScriptclass="lazy" data-src(chunkId)// create error before stack unwound to get useful stacktrace latervar error = new Error(); // =================================================onScriptComplete = function (event) {// avoid mem leaks in IE.script.onerror = script.onload = null;clearTimeout(timeout);var chunk = installedChunks[chunkId];if(chunk !== 0) {if(chunk) {var errorType = event && (event.type === 'load' ? 'missing' : event.type);var realclass="lazy" data-src = event && event.target && event.target.class="lazy" data-src;error.message = 'Loading chunk ' + chunkId + ' failed.\n(' + errorType + ': ' + realclass="lazy" data-src + ')';error.name = 'ChunkLoadError';error.type = errorType;error.request = realclass="lazy" data-src;chunk[1](error);}installedChunks[chunkId] = undefined;}};var timeout = setTimeout(function(){onScriptComplete({ type: 'timeout', target: script });}, 120000);script.onerror = script.onload = onScriptComplete;document.head.appendChild(script);}}return Promise.all(promises);};
总结一下,上述代码做的事情
如果chunk没有被加载过,会为这个chunk创建一个promise对象
将promise对象存在promises数组中
将promise的resolve 和 reject存在
installedChunks[chunkId]
中
3. 执行异步脚本
经过上面的过程,会动态加载0.js的脚本代码
(window["webpackJsonp"] = window["webpackJsonp"] || []).push([[0],{"./class="lazy" data-src/test.js":(function(module, __webpack_exports__, __webpack_require__) {"use strict";eval("__webpack_require__.r(__webpack_exports__);\n __webpack_require__.d(__webpack_exports__, \"default\", function() { return func; });\nfunction func() {\n return 1;\n}\n\n//# sourceURL=webpack:///./class="lazy" data-src/test.js?"); })}]);
可以看到window上有一个webpackJsonp数组,那么这个东西是从哪里来的呢?,我们来看下面的代码。
// bundle.jsvar jsonpArray = window["webpackJsonp"] = window["webpackJsonp"] || [];var oldJsonpFunction = jsonpArray.push.bind(jsonpArray);jsonpArray.push = webpackJsonpCallback;jsonpArray = jsonpArray.slice();for(var i = 0; i < jsonpArray.length; i++) webpackJsonpCallback(jsonpArray[i]);var parentJsonpFunction = oldJsonpFunction;
其实一开始初始化时已经覆盖实现了webpackJsonp.push
方法
(window["webpackJsonp"] = window["webpackJsonp"] || []).push([[0],{ // test.js引入的模块代码})// 等价于webpackJsonpCallback([[0],{ // test.js引入的模块代码})
下面再看看webpackJsonpCallback代码的实现
4. webpackJsonpCallback
// bundle.jsfunction webpackJsonpCallback(data) { // chunkidvar chunkIds = data[0]; // chunkid对应的模块var moreModules = data[1]var moduleId, chunkId, i = 0, resolves = [];for(;i < chunkIds.length; i++) {chunkId = chunkIds[i];if(Object.prototype.hasOwnProperty.call(installedChunks, chunkId) && installedChunks[chunkId]) { // 收集chunk对应的resolve方法resolves.push(installedChunks[chunkId][0]);} // 标记该chunk已经加载installedChunks[chunkId] = 0;}for(moduleId in moreModules) {if(Object.prototype.hasOwnProperty.call(moreModules, moduleId)) { // 添加chunk模块,到全局modules对象中modules[moduleId] = moreModules[moduleId];}}if(parentJsonpFunction) parentJsonpFunction(data) // 依次执行chunk对应promise的resolve方法while(resolves.length) {resolves.shift()();}};
还是总结一下上面代码的过程
收集chunk对应的resolve方法, 前面执行__webpack_require__.e时放在了
installedChunks[chunkId]
里将异步chunk下的所有模块 添加到 全局modules
依次执行chunk对应promise的resolve方法
5. 执行异步模块代码
回到一开始index.js的代码
Promise.all( [ __webpack_require__.e(0) ]).then( __webpack_require__.bind(null, "./class="lazy" data-src/test.js")).then(function (fn) { console.log(fn.default());}));
经过上面的步骤,此时promise已经resolve了,__webpack_require__.bind(null, "./class="lazy" data-src/test.js")
会被执行, 此时异步模块的代码已经在modules上了,所以可以直接加载。
最后,执行fn方法
console.log(fn.default());
流程图
以上就是“webpack动态import原理是什么”这篇文章的所有内容,感谢各位的阅读!相信大家阅读完这篇文章都有很大的收获,小编每天都会为大家更新不同的知识,如果还想学习更多的知识,请关注编程网行业资讯频道。
免责声明:
① 本站未注明“稿件来源”的信息均来自网络整理。其文字、图片和音视频稿件的所属权归原作者所有。本站收集整理出于非商业性的教育和科研之目的,并不意味着本站赞同其观点或证实其内容的真实性。仅作为临时的测试数据,供内部测试之用。本站并未授权任何人以任何方式主动获取本站任何信息。
② 本站未注明“稿件来源”的临时测试数据将在测试完成后最终做删除处理。有问题或投稿请发送至: 邮箱/279061341@qq.com QQ/279061341