webpack 本质就是一个模块打包器，loader 与 plugin 是打包过程中额外完成的事情。
yarn add webpack@^4.44.2 webpack-cli@^3.3.12 html-webpack-plugin@^4.5.0 -D
打包文件分析
webpack.config.js
const path = require('path');const HtmlWebpackPlugin = require('html-webpack-plugin');module.exports = {devtool: 'none',mode: 'development',entry: './src/index.js',output: {filename: 'build.js',path: path.resolve(__dirname, 'dist')},plugins: [new HtmlWebpackPlugin({template: './src/index.html'})]}
package.json
{"name": "test","version": "1.0.0","description": "","main": "index.js","scripts": {"test": "echo \"Error: no test specified\" && exit 1"},"keywords": [],"author": "","license": "ISC","devDependencies": {"html-webpack-plugin": "^4.5.0","webpack": "^4.44.2","webpack-cli": "^3.3.12"}}
index.html
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Test</title></head><body></body></html>
index.js
console.log('index.js');
module.exports = 'main entry file';
运行打包命令
npx webpack
dist/build.js
(function(modules) { // webpackBootstrap
// The module cache 缓存被加载的模块
var installedModules = {};
// The require function
// webpack 自定义方法，核心作用就是返回模块的 exports
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;
}
// 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 = "";
// Load entry module and return exports
return __webpack_require__(__webpack_require__.s = "./src/index.js");
})
({
// 定义模块路径
"./src/index.js":
// 类似 commonjs 加载
(function(module, exports) {
console.log('index.js');
module.exports = 'main entry file';
})
});
打包后的文件就是一个函数自调用，当前函数调用时传入一个对象。这个对象我们我们可以称之为模块定义。
键名是当前被加载模块的文件名与目录的拼接；键值就是一个函数，和 nodejs 里的模块加载有一些类似，会将被加载模块中的内容包裹于一个函数中，这个函数在将来某个时间点上会被调用，同时会接收到一定参数，利用这些参数可以实现模块的加载操作。
针对于上述代码相当于将 {}（模块定义） 传递给 modules 。
单文件打包后源码调试
vscode 对 dist/build.js 进行单文件调试。
功能函数说明
index.js
const name = require('./login');
console.log('index.js');
console.log(name);
module.exports = 'main entry file';
login.js
module.exports = 'education';
dist/build.js
(function(modules) { // webpackBootstrap
// The module cache
// 定义对象，用于缓存已加载过的模块
var installedModules = {};
// The require function
// Webpack 自定义加载模块方法，核心功能就是返回被加载模块的导出内容
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;
}
// expose the modules object (__webpack_modules__)
// 保存模块定义，通过 m 挂载到自定义方法上
__webpack_require__.m = modules;
// expose the module cache
//保存已经在模块，通过 c 挂载到自定义方法上
__webpack_require__.c = installedModules;
// Object.prototype.hasOwnProperty.call
// 判断当前被传入的对象，是否存在指定的属性
__webpack_require__.o = function(object, property) { return Object.prototype.hasOwnProperty.call(object, property); };
// define getter function for harmony exports
// 为 exports 定义属性，提供访问 getter
__webpack_require__.d = function(exports, name, getter) {
// 如果当前 exports 不具备 name 属性，则条件成立
if(!__webpack_require__.o(exports, name)) {
Object.defineProperty(exports, name, { enumerable: true, get: getter });
}
};
// define __esModule on exports
// 给 exports 添加标记，通过标记我们可以知道当前是 ES Modue，还是非 ES Modue
__webpack_require__.r = function(exports) {
// 如果成立说明是 ES Module
if(typeof Symbol !== 'undefined' && Symbol.toStringTag) {
// Object.prototype.toString.call(exports) => Module
Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
}
// 为 exports 添加 __esModule 属性，值为 true
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
// 调用 t 方法之后，我们可以拿到被加载模块的内容 value
// 针对 value，可以直接返回，也可以处理之后再返回
__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
// 定义 getter，返回 getter
__webpack_require__.n = function(module) {
var getter = module && module.__esModule ?
// ES Module 返回 module.default 属性
function getDefault() { return module['default']; } :
// 非 ES Module，返回 module
function getModuleExports() { return module; };
__webpack_require__.d(getter, 'a', getter);
return getter;
};
// __webpack_public_path__
// 共有路径
__webpack_require__.p = "";
// Load entry module and return exports
// .s 缓存主入口文件值
return __webpack_require__(__webpack_require__.s = "./src/index.js");
})
({
"./src/index.js":
(function(module, exports, __webpack_require__) {
const name = __webpack_require__(/*! ./login */ "./src/login.js");
console.log('index.js');
console.log(name);
module.exports = 'main entry file';
}),
"./src/login.js":
(function(module, exports) {
module.exports = 'education';
})
});
CommonJS 模块打包
webpack 默认支持的就是 common.js 规范，建议日常开发也使用 common.js 规范。
const name = require('./login');
console.log('index.js');
console.log(name);
module.exports = 'main entry file';
// commonjs 规范
module.exports = 'education';
(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] = {
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;
}
// 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 = "";
// Load entry module and return exports
return __webpack_require__(__webpack_require__.s = "./src/index.js");
})
/************************************************************************/
({
"./src/index.js":
(function(module, exports, __webpack_require__) {
const name = __webpack_require__(/*! ./login */ "./src/login.js");
console.log('index.js');
console.log(name);
module.exports = 'main entry file';
}),
"./src/login.js":
(function(module, exports) {
// commonjs 规范
module.exports = 'education';
})
});
ES Module 模块打包
// es module 规范
export default 'yueluo';
export const age = 23;
const obj = require('./login');
console.log('index.js');
console.log(obj.default, '---', obj.age);
export default 'main entry file';
(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] = {
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;
}
// 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 = "";
// Load entry module and return exports
return __webpack_require__(__webpack_require__.s = "./src/index.js");
})
({
"./src/index.js":
(function(module, __webpack_exports__, __webpack_require__) {
"use strict";
__webpack_require__.r(__webpack_exports__);
const obj = __webpack_require__(/*! ./login */ "./src/login.js");
console.log('index.js');
console.log(obj.default, '---', obj.age);
__webpack_exports__["default"] = ('main entry file');
}),
"./src/login.js":
(function(module, __webpack_exports__, __webpack_require__) {
"use strict";
__webpack_require__.r(__webpack_exports__);
__webpack_require__.d(__webpack_exports__, "age", function() { return age; });
// es module 规范
__webpack_exports__["default"] = ('yueluo');
const age = 23;
})
});
对于 webpack 打包操作来说，我们可以使用 commonjs 规范，也可以使用 esmodule 规范。不过在最终打包处理时，针对于产出内容，采用 commonjs 规范，加载 commonjs 规范导出的内容生成的代码是最少的。不过也要看实际情况，推荐使用 commonjs 规范进行打包处理。
功能函数手写实现
src/login.js
module.exports = 'education';
src/index.js
const name = require('./login');
console.log('index：', name);
shared/build.js
(function (modules) {
// 缓存被加载的模块
const installedModules = {};
// 定义 __webpack_require__ 方法替换 require
function __webpack_require__ (moduleId) {
// 判断当前缓存中是否存在要被加载的模块内容，如果存在，直接返回
if (installedModules[moduleId]) {
return installedModules[moduleId].exports;
}
// 如果当前缓存中不存在，定义对象
const module = installedModules[moduleId] = {
i: moduleId,
l: false,
exports: {}
};
// 调用当前 moduleId 对应的函数，完成内容加载
modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
// 当上述方法调用完成之后，就可以修改 l 的值用于表示当前模块内容已加载完成
module.l = true;
// 加载完成之后，将模块内容返回至调用位置
return module.exports;
}
// 定义 m 属性保存 modules
__webpack_require__.m = modules;
// 定义 c 属性保存 cache
__webpack_require__.c = installedModules;
// 定义 o 方法用于对象身上是否存在指定属性
__webpack_require__.o = function (object, property) {
return Object.prototype.hasOwnProperty.call(object, property);
}
// 定义 d 方法用于在对象身上添加指定属性及 getter
__webpack_require__.d = function (exports, name, getter) {
if (!__webpack_require__.o(exports, name)) {
Object.defineProperty(exports, name, { enumerable: true, get: getter });
}
}
// 定义 r 方法用于标识当前模块是 ES6 类型
__webpack_require__.r = function (exports) {
if (typeof Symbol !== 'undefined' && Symbol.toStringTag) {
Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
}
Object.defineProperty(exports, '__esModule', { value: true })
}
// 定义 n 方法用于设置具体 getter
__webpack_require__.n = function (module) {
let getter = module && module.__esModule ? (
function getDefault () { return module['default'] }
) : (
function getModuleExports () { return module }
);
__webpack_require__.d(getter, 'a', getter);
return getter;
}
// 定义 p 属性用于保存资源访问路径
__webpack_require__.p = "";
// 调用 __webpack_require__ 方法执行模块导入与加载操作
return __webpack_require__(__webpack_require__.s = './src/index.js');
})
({
"./src/index.js": (function (module, exports, __webpack_require__) {
// commonjs 规范
// const name = __webpack_require__("./src/login.js");
// console.log('index：', name);
// esmodule 规范
"use strict";
__webpack_require__.r(exports);
var _login__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__("./src/login.js");
var _login__WEBPACK_IMPORTED_MODULE_0___default = __webpack_require__.n(_login__WEBPACK_IMPORTED_MODULE_0__);
// const name = require('./login');
console.log('index：', _login__WEBPACK_IMPORTED_MODULE_0___default.a);
}),
"./src/login.js": (function (module, exports) {
module.exports = 'education';
})
});
dist/index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Test</title>
</head>
<body>
<script src="../shared/build.js"></script></body>
</html>
懒加载实现流程梳理
login.js
export default 'yueluo';
export const age = 23;
index.js
const oBtn = document.getElementById('J-btn');
console.log('index');
oBtn.addEventListener('click', () => {
import(/*webpackChunkName: 'login'*/'./login.js')
.then(login => {
console.log(login);
})
.catch(err => {
console.log(err);
})
});
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Test</title>
</head>
<body>
<button id="J-btn">Click</button>
</body>
</html>
dist/build.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 jsonpScriptSrc(chunkId) {
return __webpack_require__.p + "" + chunkId + ".build.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.src = jsonpScriptSrc(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 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;
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 = "./src/index.js");
})
/************************************************************************/
({
"./src/index.js":
(function(module, exports, __webpack_require__) {
const oBtn = document.getElementById('J-btn');
console.log('index');
oBtn.addEventListener('click', () => {
__webpack_require__.e(/*! import() | login */ "login").then(__webpack_require__.bind(null, /*! ./login.js */ "./src/login.js"))
.then(login => {
console.log(login);
})
.catch(err => {
console.log(err);
})
});
})
});
dist/login.build.js
(window["webpackJsonp"] = window["webpackJsonp"] || []).push([["login"],{
"./src/login.js":
(function(module, __webpack_exports__, __webpack_require__) {
"use strict";
__webpack_require__.r(__webpack_exports__);
__webpack_require__.d(__webpack_exports__, "age", function() { return age; });
__webpack_exports__["default"] = ('yueluo');
const age = 23;
})
}]);
import 可以实现指定模块的懒加载操作，懒加载的核心原理就是 JSONP。
t 方法可以针对内容进行不同的处理，处理方式取决于传入的数值（8，6，3，7，2，1）。
t 方法分析及实现
方法分析
(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] = {
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;
}
// 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) {
// 接收两个参数，value 是被加载的模块 ID，第二个值是二进制的数值
// t 方法内部做的第一件事就是调用自定义 require 方法，加载对应内容重新赋值给 value
// 当获取到 value 值之后，余下的 8、4、2 都是对当前的内容进行加工处理，然后返回使用
// 1. 当 mode & 8 成立，直接将 value 返回（1、8 同时成立，相当于加载 commonjs 规范内容）
// 2. 当 mode & 4 成立，直接将 value 返回（1、3 同时成立，相当于加载 esmodule 规范内容）
// 3. 上述条件不成立，首先定义 ns 空对象
// 3.1 如果 value 是一个可以用直接使用的值，例如字符串，将 value 挂载到 default 属性上
// 3.2 如果 value 是一个对象，遍历对象，调用 d 方法，将对象属性定义到 ns 上
// 3.3 返回 ns 对象
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 = "";
// Load entry module and return exports
return __webpack_require__(__webpack_require__.s = "./src/index.js");
})
/************************************************************************/
({
"./src/index.js":
(function(module, exports, __webpack_require__) {
const name = __webpack_require__(/*! ./login */ "./src/login.js");
console.log('index');
console.log(name);
}),
"./src/login.js":
(function(module, exports) {
module.exports = 'education';
})
});
let mode = 0b1001;
if (mode & 1) {
console.log('第四位上的值是 1');
}
if (mode & 8) {
console.log('第一位上的值是 1');
}
方法实现
(function (modules) {
// 缓存被加载的模块
const installedModules = {};
// 定义 __webpack_require__ 方法替换 require
function __webpack_require__ (moduleId) {
// 判断当前缓存中是否存在要被加载的模块内容，如果存在，直接返回
if (installedModules[moduleId]) {
return installedModules[moduleId].exports;
}
// 如果当前缓存中不存在，定义对象
const module = installedModules[moduleId] = {
i: moduleId,
l: false,
exports: {}
};
// 调用当前 moduleId 对应的函数，完成内容加载
modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
// 当上述方法调用完成之后，就可以修改 l 的值用于表示当前模块内容已加载完成
module.l = true;
// 加载完成之后，将模块内容返回至调用位置
return module.exports;
}
// 定义 m 属性保存 modules
__webpack_require__.m = modules;
// 定义 c 属性保存 cache
__webpack_require__.c = installedModules;
// 定义 o 方法用于对象身上是否存在指定属性
__webpack_require__.o = function (object, property) {
return Object.prototype.hasOwnProperty.call(object, property);
}
// 定义 d 方法用于在对象身上添加指定属性及 getter
__webpack_require__.d = function (exports, name, getter) {
if (!__webpack_require__.o(exports, name)) {
Object.defineProperty(exports, name, { enumerable: true, get: getter });
}
}
// 定义 r 方法用于标识当前模块是 ES6 类型
__webpack_require__.r = function (exports) {
if (typeof Symbol !== 'undefined' && Symbol.toStringTag) {
Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
}
Object.defineProperty(exports, '__esModule', { value: true })
}
// 定义 n 方法用于设置具体 getter
__webpack_require__.n = function (module) {
let getter = module && module.__esModule ? (
function getDefault () { return module['default'] }
) : (
function getModuleExports () { return module }
);
__webpack_require__.d(getter, 'a', getter);
return getter;
}
// 定义 t 方法用于加载指定 value 的模块内容，对内容进行处理并返回
__webpack_require__.t = function (value, mode) {
// 加载 value 对应的模块内容（value 通常是模块 ID）
if (mode & 1) {
value = __webpack_require__(value);
}
// commonjs
if (mode & 8) {
return value;
}
// esmodule
if ((mode & 4 && typeof value === 'object' && value && value.__esModule)) {
return value;
}
// 如果 8 和 4 都不成立，则需要自定义 ns，通过 default 属性返回内容
const ns = Object.create(null);
__webpack_require__.r(ns);
Object.defineProperty(ns, 'default', { enumerable: true, value });
if (mode & 2 && typeof value !== 'string') {
for (const k in value) {
__webpack_require__.d(ns, k, function (key) {
return value[key];
}.bind(null, k));
}
}
return ns;
}
// 定义 p 属性用于保存资源访问路径
__webpack_require__.p = "";
// 调用 __webpack_require__ 方法执行模块导入与加载操作
return __webpack_require__(__webpack_require__.s = './src/index.js');
})
({
"./src/index.js": (function (module, exports, __webpack_require__) {
// const name = __webpack_require__("./src/login.js");
// console.log('index：', name);
"use strict";
// __webpack_require__.r(exports);
// var _login__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__("./src/login.js");
// var _login__WEBPACK_IMPORTED_MODULE_0___default = __webpack_require__.n(_login__WEBPACK_IMPORTED_MODULE_0__);
// const name = require('./login');
const name = __webpack_require__.t("./src/login.js", 0b0111);
console.log(name);
// console.log('index：', _login__WEBPACK_IMPORTED_MODULE_0___default.a);
}),
"./src/login.js": (function (module, exports) {
module.exports = {
name: 'yueluo',
age: 23
};
})
});
单文件懒加载源码分析
login.js
module.exports = 'lazy load';
index.js
const oBtn = document.getElementById('J-btn');
oBtn.addEventListener('click', function () {
import(/* webpackChunkName: "login" */ './login.js').then(content => {
console.log(content);
})
});
console.log('index');
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Test</title>
</head>
<body>
<button id="J-btn">Click</button>
</body>
</html>
dist/login.build.js
(window["webpackJsonp"] = window["webpackJsonp"] || []).push([["login"],{
"./src/login.js":
(function(module, exports) {
module.exports = 'lazy load';
})
}]);
dist/build.js
(function(modules) { // webpackBootstrap
// install a JSONP callback for chunk loading
// 模块依赖关系合并、将 promise 变成成功态，方便调用
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) {
// 模块合并
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 jsonpScriptSrc(chunkId) {
return __webpack_require__.p + "" + chunkId + ".build.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.src = jsonpScriptSrc(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 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;
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 = "./src/index.js");
})
/************************************************************************/
({
"./src/index.js":
(function(module, exports, __webpack_require__) {
const oBtn = document.getElementById('J-btn');
oBtn.addEventListener('click', function () {
__webpack_require__.e(/*! import() | login */ "login").then(__webpack_require__.t.bind(null, /*! ./login.js */ "./src/login.js", 7)).then(content => {
console.log(content);
})
});
console.log('index');
})
});
单文件懒加载实现
dist/index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Test</title>
</head>
<body>
<button id="J-btn">Click</button>
<script src="../shared/build.js"></script></body>
</html>
dist/login.build.js
(window["webpackJsonp"] = window["webpackJsonp"] || []).push([["login"],{
/***/ "./src/login.js":
/*!**********************!*\
!*** ./src/login.js ***!
\**********************/
/*! no static exports found */
/***/ (function(module, exports) {
module.exports = 'lazy load';
/***/ })
}]);
shared/build.js
(function (modules) {
// 定义 webpackJsonpCallback：合并模块定义、改变 Promise 状态，执行后续行为
function webpackJsonpCallback (data) {
// 获取需要被加载的模块 ID
const chunkIds = data[0];
// 获取需要被动态加载的模块依赖关系对象
const moreModules = data[1];
let chunkId, resolves = [];
// 循环判断 chunkIds 里对应的模块内容是否已经完成加载
for (let i = 0; i < chunkIds.length; i++) {
chunkId = chunkIds[i];
if (Object.prototype.hasOwnProperty.call(installedChunks, chunkId) && installedChunks[chunkId]) {
resolves.push(installedChunks[chunkId][0]);
}
// 更新当前 chunk 状态
installedChunks[chunkId] = 0;
}
for (moduleId in moreModules) {
if (Object.prototype.hasOwnProperty.call(moreModules, moduleId)) {
modules[moduleId] = moreModules[moduleId];
}
}
while (resolves.length) {
resolves.shift()();
}
}
// 缓存被加载的模块
const installedModules = {};
// 定义 installedChunks 对于用于标识某个 chunkId 对应 chunk 是否完成加载
// 0 已加载过、promises 正在加载、null/undefiend 未加载
var installedChunks = {
main: 0
}
// 定义 __webpack_require__ 方法替换 require
function __webpack_require__ (moduleId) {
// 判断当前缓存中是否存在要被加载的模块内容，如果存在，直接返回
if (installedModules[moduleId]) {
return installedModules[moduleId].exports;
}
// 如果当前缓存中不存在，定义对象
const module = installedModules[moduleId] = {
i: moduleId,
l: false,
exports: {}
};
// 调用当前 moduleId 对应的函数，完成内容加载
modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
// 当上述方法调用完成之后，就可以修改 l 的值用于表示当前模块内容已加载完成
module.l = true;
// 加载完成之后，将模块内容返回至调用位置
return module.exports;
}
// 定义 m 属性保存 modules
__webpack_require__.m = modules;
// 定义 c 属性保存 cache
__webpack_require__.c = installedModules;
// 定义 o 方法用于对象身上是否存在指定属性
__webpack_require__.o = function (object, property) {
return Object.prototype.hasOwnProperty.call(object, property);
}
// 定义 d 方法用于在对象身上添加指定属性及 getter
__webpack_require__.d = function (exports, name, getter) {
if (!__webpack_require__.o(exports, name)) {
Object.defineProperty(exports, name, { enumerable: true, get: getter });
}
}
// 定义 r 方法用于标识当前模块是 ES6 类型
__webpack_require__.r = function (exports) {
if (typeof Symbol !== 'undefined' && Symbol.toStringTag) {
Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
}
Object.defineProperty(exports, '__esModule', { value: true })
}
// 定义 n 方法用于设置具体 getter
__webpack_require__.n = function (module) {
let getter = module && module.__esModule ? (
function getDefault () { return module['default'] }
) : (
function getModuleExports () { return module }
);
__webpack_require__.d(getter, 'a', getter);
return getter;
}
// 定义 jsonpScriptSrc 实现 src 的处理
function jsonpScriptSrc (chunkId) {
return __webpack_require__.p + "" + chunkId + '.build.js';
}
// 定义 e 方法用于实现 jsonp 来加载内容，利用 promise 实现异步加载操作
__webpack_require__.e = function (chunkId) {
// 定义一个数组用于存放 promise
let promises = [];
// 获取 chunkId 对应的 chunk 是否已经完成加载
let installedChunkData = installedChunks[chunkId];
// 根据当前是否已完成加载的状态来执行后续逻辑
if (installedChunkData !== 0) {
if (installedChunkData) {
promises.push(installedChunkData[2]);
} else {
const promise = new Promise((resolve, reject) => {
installedChunkData = installedChunks[chunkId] = [resolve, reject];
});
promises.push(installedChunkData[2] = promise);
// 创建标签
const script = document.createElement('script');
// 设置 src
script.src = jsonpScriptSrc(chunkId);
// 写入 scrpit 标签
document.head.appendChild(script);
}
}
// 执行 promise
return Promise.all(promises);
}
// 定义 t 方法用于加载指定 value 的模块内容，对内容进行处理并返回
__webpack_require__.t = function (value, mode) {
// 加载 value 对应的模块内容（value 通常是模块 ID）
if (mode & 1) {
value = __webpack_require__(value);
}
// commonjs
if (mode & 8) {
return value;
}
// esmodule
if ((mode & 4 && typeof value === 'object' && value && value.__esModule)) {
return value;
}
// 如果 8 和 4 都不成立，则需要自定义 ns，通过 default 属性返回内容
const ns = Object.create(null);
__webpack_require__.r(ns);
Object.defineProperty(ns, 'default', { enumerable: true, value });
if (mode & 2 && typeof value !== 'string') {
for (const k in value) {
__webpack_require__.d(ns, k, function (key) {
return value[key];
}.bind(null, k));
}
}
return ns;
}
// 定义 p 属性用于保存资源访问路径
__webpack_require__.p = "";
// 定义变量存放数组
const jsonpArray = window['webpackJsonp'] = window['webpackJsonp'] || [];
// 保存原生的 push 方法
const oldJsonpFunction = jsonpArray.push.bind(jsonpArray);
// 重写原生的 push 方法
jsonpArray.push = webpackJsonpCallback;
// 调用 __webpack_require__ 方法执行模块导入与加载操作
return __webpack_require__(__webpack_require__.s = './src/index.js');
})
({
"./src/index.js":
(function(module, exports, __webpack_require__) {
const oBtn = document.getElementById('J-btn');
oBtn.addEventListener('click', function () {
__webpack_require__.e(/*! import() | login */ "login").then(__webpack_require__.t.bind(null, /*! ./login.js */ "./src/login.js", 7)).then(content => {
console.log(content);
})
});
console.log('index');
})
});
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