## 1. webpack介绍
Webpack
是一个前端资源加载/打包工具。它将根据模块的依赖关系进行静态分析,然后将这些模块按照指定的规则生成对应的静态资源。Symbol.toStringTag
是一个内置 symbol,它通常作为对象的属性键使用,对应的属性值应该为字符串类型,这个字符串用来表示该对象的自定义类型标签,通常只有内置的 Object.prototype.toString()
方法会去读取这个标签并把它包含在自己的返回值里。console.log(Object.prototype.toString.call('foo')); // "[object String]"
console.log(Object.prototype.toString.call([1, 2])); // "[object Array]"
console.log(Object.prototype.toString.call(3)); // "[object Number]"
console.log(Object.prototype.toString.call(true)); // "[object Boolean]"
console.log(Object.prototype.toString.call(undefined)); // "[object Undefined]"
console.log(Object.prototype.toString.call(null)); // "[object Null]"
let myExports={};
Object.defineProperty(myExports, Symbol.toStringTag, { value: 'Module' });
console.log(Object.prototype.toString.call(myExports));
create
创建的对象,没有任何属性,把它当作一个非常纯净的map来使用,我们可以自己定义hasOwnProperty
、toString
方法,完全不必担心会将原型链上的同名方法覆盖掉for..in
循环的时候会遍历对象原型链上的属性,使用create(null)
就不必再对属性进行检查了var ns = Object.create(null);
if (typeof Object.create !== "function") {
Object.create = function (proto) {
function F() {}
F.prototype = proto;
return new F();
};
}
console.log(ns)
console.log(Object.getPrototypeOf(ns));
configurable | enumerable | value | writable | get | set | |
---|---|---|---|---|---|---|
数据描述符 | Yes | Yes | Yes | Yes | No | No |
存取描述符 | Yes | Yes No | No | Yes | Yes |
var ageValue = 10;
let obj = {};
Object.defineProperty(obj, "age", {
//value: 10,//数据描述符和存取描述符不能混合使用
get() {
return ageValue;
},
set(newValue) {
ageValue = newValue;
},
//writable: true,//是否可修改
enumerable: true,//是否可枚举
configurable: true//是否可配置可删除
});
Object.defineProperty(obj, "name", {
value: 'zhufeng',//数据描述符和存取描述符不能混合使用
writable: true,//是否可修改
enumerable: true,//是否可枚举
configurable: true//是否可配置可删除
});
console.log(obj.age, obj.name);
obj.age = 100;
obj.name = 'jiagou';
console.log(obj.age, obj.name);
const path = require('path');
const HtmlWebpackPlugin=require('html-webpack-plugin');
module.exports = {
mode:'development',
devtool:"none",
context: process.cwd(),
entry: './src/index.js',
output: {
filename: 'bundle.js'
},
devServer:{
contentBase:path.resolve(__dirname,'./dist')
},
module: {
rules: [
{
test: /\.js$/,
use: {
loader: "babel-loader",
options: {
presets:["@babel/preset-env"]
}
},
include: path.join(__dirname, "src"),
exclude: /node_modules/
}
]
},
plugins: []
};
src\index.js
let title = require('./title.js');
console.log(title);
src\title.js
module.exports = "title";
(function(modules) {
// webpack的启动函数
//模块的缓存
var installedModules = {};
//定义在浏览器中使用的require方法
function __webpack_require__(moduleId) {
//检查模块是否在缓存中
if (installedModules[moduleId]) {
return installedModules[moduleId].exports;
}
//创建一个新的模块并且放到模块的缓存中
var module = (installedModules[moduleId] = {
i: moduleId,
l: false,
exports: {}
});
//执行模块函数
modules[moduleId].call(
module.exports,
module,
module.exports,
__webpack_require__
);
//把模块设置为已经加载
module.l = true;
//返回模块的导出对象
return module.exports;
}
//暴露出模块对象
__webpack_require__.m = modules;
//暴露出模块缓存
__webpack_require__.c = installedModules;
//为harmony导出定义getter函数
__webpack_require__.d = function(exports, name, getter) {
if (!__webpack_require__.o(exports, name)) {
Object.defineProperty(exports, name, { enumerable: true, get: getter });
}
};
//在导出对象上定义__esModule属性
__webpack_require__.r = function(exports) {
if (typeof Symbol !== "undefined" && Symbol.toStringTag) {
Object.defineProperty(exports, Symbol.toStringTag, { value: "Module" });
}
Object.defineProperty(exports, "__esModule", { value: true });
};
/**
* 创建一个模拟的命名空间对象
* mode & 1 value是模块ID直接用__webpack_require__加载
* mode & 2 把所有的属性合并到命名空间ns上
* mode & 4 当已经是命名空间的时候(__esModule=true)可以直接返回值
* mode & 8|1 行为类似于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); //定义一个空对象
__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函数为了兼容那些非non-harmony模块
__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;
};
//判断对象身上是否拥有此属性
__webpack_require__.o = function(object, property) {
return Object.prototype.hasOwnProperty.call(object, property);
};
//公共路径
__webpack_require__.p = "";
//加载入口模块并且返回导出对象
return __webpack_require__((__webpack_require__.s = "./src/index.js"));
})({
"./src/index.js": function(module, exports, __webpack_require__) {
var title = __webpack_require__("./src/title.js");
console.log(title);
},
"./src/title.js": function(module, exports) {
module.exports = "title";
}
});
(function(modules){
var installedModules = {};
function __webpack_require__(moduleId){
if(installedModules[moduleId]){
return installedModules[moduleId];
}
var module = installedModules[moduleId] = {
i:moduleId,
l:false,
exports:{}
}
modules[moduleId].call(modules.exports,module,module.exports,__webpack_require__);
module.l = true;
return module.exports;
}
return __webpack_require__((__webpack_require__.s = "./src/index.js"));
})({
"./src/index.js":function(module,exports,__webpack_require__){
var title = __webpack_require__('./src/title.js');
console.log(title);
},
"./src/title.js":function(module,exports){
module.exports = "title";
}
})
getter
的方式增加属性function d(exports, name, getter) {
if (!exports.hasOwnProperty(name)) {
Object.defineProperty(exports, name, { get: getter });
}
}
let obj = {};
function ageGetter() {
return 10;
}
d(obj, 'age', ageGetter);
console.log(obj.age);
function r(exports) {
Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
Object.defineProperty(exports, '__esModule', { enumerable: true, value: true });
};
let obj2 = {};
r(obj2);
console.log(obj2);
function n(module) {
var getter = module.__esModule ?
function () { return module['default']; } :
function () { return module; };
d(getter, 'a', getter);
return getter;
};
let m = { age: 10 };
let getter = n(m);
console.log(getter.a);
let m2 = { default: { age: 20 }, __esModule: true };
let getter2 = n(m2);
console.log(getter2.a);
let modules = {
//相当于require
'moduleA': function (module, exports) {
module.exports = 'moduleA导出内容';
},
//是ES6模块直接返回
'moduleB': function (module, exports) {
module.exports = { __esModule: true, default: 'moduleB导出内容' };
},
//封装成ES6模块
'moduleC': function (module, exports) {
module.exports = { name: 'moduleC导出内容' };
}
}
function __webpack_require__(moduleId) {
var module = {
i: moduleId,
l: false,
exports: {}
}
modules[moduleId].call(modules.exports, module, module.exports, __webpack_require__);
module.l = true;
return module.exports;
}
function t(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);
Object.defineProperty(ns, Symbol.toStringTag, { value: 'Module' });
Object.defineProperty(ns, '__esModule', { enumerable: true, value: true });
Object.defineProperty(ns, 'default', { enumerable: true, value: value });
if (mode & 2 && typeof value != 'string')
for (var key in value)
Object.defineProperty(ns, key, { enumerable: true, get: () => value[key] });
return ns;
};
let result1 = t('moduleA', 0b1001);
console.log(result1);
let result2 = t('moduleB', 0b0101);
console.log(result2);
let result3 = t('moduleC', 0b0011);
console.log(result3, result3.name);
let title = require('./title');
console.log(title.name);
console.log(title.age);
exports.name = 'title_name';
exports.age = 'title_age';
{
"./src/index.js":
(function(module, exports, __webpack_require__) {
var title = __webpack_require__("./src/title.js");
console.log(title.name);
console.log(title.age);
}),
"./src/title.js":
(function(module, exports) {
exports.name = 'title_name';
exports.age = 'title_age';
})
}
let title = require('./title');
console.log(title);
console.log(title.default);
console.log(title.age);
export default name = 'title_name';
export const age = 'title_age';
{
"./src/index.js":
(function (module, exports, __webpack_require__) {
var title = __webpack_require__(/*! ./title */ "./src/title.js");
console.log(title.name);
console.log(title.age);
}),
"./src/title.js":
(function (module, __webpack_exports__, __webpack_require__) {
__webpack_require__.r(__webpack_exports__);
/* harmony export (binding) */
__webpack_require__.d(__webpack_exports__, "age", function () { return age; });
/* harmony default export */
__webpack_exports__["default"] = (name = 'title_name');
var age = 'title_age';
})
}
import name,{age} from './title';
console.log(name);
console.log(age);
export default name = 'title_name';
export const age = 'title_age';
{
"./src/index.js":
(function (module, __webpack_exports__, __webpack_require__) {
"use strict";
__webpack_require__.r(__webpack_exports__);
var _title__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__(/*! ./title */ "./src/title.js");
console.log(_title__WEBPACK_IMPORTED_MODULE_0__["default"]);
console.log(_title__WEBPACK_IMPORTED_MODULE_0__["age"]);
}),
"./src/title.js":
(function (module, __webpack_exports__, __webpack_require__) {
__webpack_require__.r(__webpack_exports__);
__webpack_require__.d(__webpack_exports__, "age", function () { return age; });
__webpack_exports__["default"] = (name = 'title_name');
var age = 'title_age';
})
}
import home, { name, age } from './title';
console.log(name);
console.log(age);
console.log(home);
module.exports = { home: 'beijing' };
module.exports.name = 'title_name';
module.exports.age = 'title_age';
{
"./src/index.js":
(function (module, __webpack_exports__, __webpack_require__) {
__webpack_require__.r(__webpack_exports__);
/* harmony import */ var _title__WEBPACK_IMPORTED_MODULE_0__ = __webpack_require__(/*! ./title */ "./src/title.js");
/* harmony import */ var _title__WEBPACK_IMPORTED_MODULE_0___default = /*#__PURE__*/__webpack_require__.n(_title__WEBPACK_IMPORTED_MODULE_0__);
console.log(_title__WEBPACK_IMPORTED_MODULE_0__["name"]);
console.log(_title__WEBPACK_IMPORTED_MODULE_0__["age"]);
console.log(_title__WEBPACK_IMPORTED_MODULE_0___default.a);
}),
"./src/title.js":
(function (module, exports) {
module.exports = {
home: 'beijing'
};
module.exports.name = 'title_name';
module.exports.age = 'title_age';
})
}
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
</body>
</html>
src\index.js
let button = document.createElement("button");
button.innerHTML = "点我";
button.onclick = function () {
import(/*webpackChunkName: 'title'*/'./title.js').then(function (result) {
console.log(result, result.default);
});
};
document.body.appendChild(button);
src\title.js
module.exports = {
name: 'title'
}
module.exports.age = 10;
(function (modules) { // 启动函数
//安装一个为了加载额外代码块的JSON回调函数
function webpackJsonpCallback(data) {
var chunkIds = data[0];//代码块ID
var moreModules = data[1];//更多的模块
//向模块对象上增加更多的模块,然后把所有的chunkIds设置为已经加载并触发回调
var moduleId, chunkId, i = 0, resolves = [];
for (; i < chunkIds.length; i++) {
chunkId = chunkIds[i];
if (installedChunks[chunkId]) {
resolves.push(installedChunks[chunkId][0]);
}
installedChunks[chunkId] = 0;//标识这个代码块为已经OK
}
for (moduleId in moreModules) {//把新拉下来的模块合并到模块对象上
if (Object.prototype.hasOwnProperty.call(moreModules, moduleId)) {
modules[moduleId] = moreModules[moduleId];
}
}
if (parentJsonpFunction) parentJsonpFunction(data);//如果有父JSONP函数就调用
while (resolves.length) {
resolves.shift()();//让所有的promise都OK
}
};
// 模块缓存
var installedModules = {};
//用来存放加载完成或加载中的代码块对象
// undefined = 代码块未加载, null = 代码块正在预加载或者预获取
// Promise = 代码块更在加载中, 0 = 代码块已经加载
var installedChunks = {
"main": 0
};
//JSON加载的路径
function jsonpScriptSrc(chunkId) {
return __webpack_require__.p + "" + chunkId + ".bundle.js"
}
function __webpack_require__(moduleId) {
if (installedModules[moduleId]) {
return installedModules[moduleId].exports;
}
var module = installedModules[moduleId] = {
i: moduleId,
l: false,
exports: {}
};
modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
module.l = true;
return module.exports;
}
//这个文件只包含入口代码块
//用来加载额外的代码块的函数
__webpack_require__.e = function requireEnsure(chunkId) {
var promises = [];
//JSONP代码块加载
var installedChunkData = installedChunks[chunkId];
if (installedChunkData !== 0) { // 0的意思是已经安装
// a Promise means "currently loading". 如果是一个Promise的话表示正在加载
if (installedChunkData) {
promises.push(installedChunkData[2]);//如果已经在加载中了,则添加Promise
} else {
//在代码块缓存中放置Promise
var promise = new Promise(function (resolve, reject) {
installedChunkData = installedChunks[chunkId] = [resolve, reject];
});
promises.push(installedChunkData[2] = promise);
// 开始加载代码块
var script = document.createElement('script');
var onScriptComplete;
script.charset = 'utf-8';
script.timeout = 120;
//// HTMLElement 接口的 nonce 属性返回只使用一次的加密数字,被内容安全政策用来决定这次请求是否被允许处理。
if (__webpack_require__.nc) {
script.setAttribute("nonce", __webpack_require__.nc);
}
//设置源文件路径
script.src = jsonpScriptSrc(chunkId);
//在栈展开之前创建错误以获取有用的堆栈信息
var error = new Error();
onScriptComplete = function (event) {
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);
};
__webpack_require__.m = modules;
__webpack_require__.c = installedModules;
__webpack_require__.d = function (exports, name, getter) {
if (!__webpack_require__.o(exports, name)) {
Object.defineProperty(exports, name, { enumerable: true, get: getter });
}
};
__webpack_require__.r = function (exports) {
if (typeof Symbol !== 'undefined' && Symbol.toStringTag) {
Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
}
Object.defineProperty(exports, '__esModule', { value: true });
};
__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;
};
__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;
};
__webpack_require__.o = function (object, property) { return Object.prototype.hasOwnProperty.call(object, property); };
__webpack_require__.p = "";
//异步加载中的错误处理函数
__webpack_require__.oe = function (err) { console.error(err); throw err; };
//刚开始的时候会把数组赋给window["webpackJsonp"],并且赋给jsonpArray
var jsonpArray = window["webpackJsonp"] = window["webpackJsonp"] || [];
//绑定push函数为oldJsonpFunction
var oldJsonpFunction = jsonpArray.push.bind(jsonpArray);
//狸猫换太子,把webpackJsonpCallback赋给了jsonpArray.push方法
jsonpArray.push = webpackJsonpCallback;
//把数组进行截取得到一个新的数组
jsonpArray = jsonpArray.slice();
//如果数组不为空,就把全部安装一次
for (var i = 0; i < jsonpArray.length; i++) webpackJsonpCallback(jsonpArray[i]);
//把oldJsonpFunction赋给parentJsonpFunction
var parentJsonpFunction = oldJsonpFunction;
return __webpack_require__(__webpack_require__.s = "./src/index.js");
})
({
"./src/index.js":
(function (module, exports, __webpack_require__) {
var button = document.createElement("button");
button.innerHTML = "点我";
button.onclick = function () {
__webpack_require__.e("title").then(__webpack_require__.t.bind(null, "./src/title.js", 7)).then(function (result) {
console.log(result["default"]);
});
};
document.body.appendChild(button);
})
});
dist\title.bundle.js
(window["webpackJsonp"] = window["webpackJsonp"] || []).push([["title"], {
"./src/title.js":
(function (module, exports) {
module.exports = {
name: 'title'
};
module.exports.age = 10;
})
}]);
(function (modules) {
var installedModules = {};
function __webpack_require__(moduleId) {
if (installedModules[moduleId]) {
return installedModules[moduleId].exports;
}
var module = installedModules[moduleId] = {
i: moduleId,
l: false,
exports: {}
}
modules[moduleId].call(modules.exports, module, module.exports, __webpack_require__);
module.l = true;
return module.exports;
}
var installedChunks = {
"main": 0
};
function webpackJsonpCallback(data) {
var chunkIds = data[0];//代码块ID
var moreModules = data[1];//更多的模块
var moduleId, chunkId, resolves = [];
for (let i = 0; i < chunkIds.length; i++) {
chunkId = chunkIds[i];
resolves.push(installedChunks[chunkId][0]);
installedChunks[chunkId] = 0;//标识这个代码块为已经OK
}
for (moduleId in moreModules) {//把新拉下来的模块合并到模块对象上
modules[moduleId] = moreModules[moduleId];
}
while (resolves.length) {
resolves.shift()();//让所有的promise都OK
}
}
__webpack_require__.t = function (value) {
value = __webpack_require__(value);
var ns = Object.create(null);
ns.default = value;
return ns;
};
__webpack_require__.e = function (chunkId) {
var promises = [];
var installedChunkData = installedChunks[chunkId];
if (installedChunkData !== 0) {
var promise = new Promise(function (resolve, reject) {
installedChunkData = installedChunks[chunkId] = [resolve, reject];
});
installedChunkData[2] = promise;
promises.push(promise);
var script = document.createElement('script');
script.src = chunkId + ".bundle.js";
document.head.appendChild(script);
}
return Promise.all(promises);
}
var jsonpArray = window["webpackJsonp"] = window["webpackJsonp"] || [];
jsonpArray.push = webpackJsonpCallback;
return __webpack_require__("./src/index.js");
})({
"./src/index.js":
(function (module, exports, __webpack_require__) {
var button = document.createElement("button");
button.innerHTML = "点我";
button.onclick = function () {
__webpack_require__.e("title").then(__webpack_require__.t.bind(null, "./src/title.js", 7)).then(function (result) {
console.log(result["default"]);
});
};
document.body.appendChild(button);
})
})