详解webpack分包及异步加载套路

 var path = require('path'),
 DashboardPlugin = require('webpack-dashboard/plugin'),
 HtmlWebpackPlugin = require('html-webpack-plugin'),
 webpack = require('webpack'),
 ExtractTextPlugin = require('extract-text-webpack-plugin');

var PATHS = {
 app: path.join(__dirname, 'src'),
 dist: path.join(__dirname, 'dist')
}

var PKG = require('./package.json');
var TARGET = process.env.npm_lifecycle_event; //获取当前正在运行的脚本名称

var isProduction = function() {
 return process.env.NODE_ENV === 'production';
}



module.exports ={
 entry: {
 'index': path.join(__dirname, 'src/index.js'),
 'lib': ['./src/lib/js/index.js'],
 },
 //filename是主入口文件的名称,即对应的entry
 //chunkFilename对应的是非主入口文件的名称,chunk
 output: {
 path: PATHS.dist,
 publicPath: '/static/taxi-driver/', //publicPath 的话是打包的时候生成的文件链接,如果是在生产环境当然是用服务器地址，如果是开发环境就是用本地静态服务器的地址
 filename: 'js/register/[name].js',
 chunkFilename: 'js/register/[name].js',
 //TODO: build文件中加入hash值
 },
 //生成source-map文件
 devtool: isProduction ? null : 'source-map',
 devServer: {
 proxy: {
  '/api/*': {
  target: 'http://localhost:3000',
  secure: false
  }
 }
 },
 module: {
 loaders: [
  {
  test: /\.js$/,
  exclude: /node_modules|picker.min.js/,
  loader: 'babel'
  },
  {
  test: /\.less$/,
  loader: ExtractTextPlugin.extract('style', 'css!less')
  },
  {
  test: /\.html$/,
  loader: 'raw'
  },
  {
  test: /\.css$/,
  loader: ExtractTextPlugin.extract('style', 'css')
  },
  {
  test: /\.json$/,
  loader: 'json'
  }
 ]
 },
 resolve: {
 alias: {
  src: path.join(__dirname, 'src'),
  modules: path.join(__dirname, 'src/modules'),
  lessLib: path.join(__dirname, 'src/lib/less'), 
  jsLib: path.join(__dirname, 'src/lib/js'),
  components: path.join(__dirname, 'src/components')
 },
 extensions: ['', '.js', '.less', '.html', '.json'],
 },
 plugins: [
 new HtmlWebpackPlugin({
  title: '认证资料',
  template: './dist/assets/info.html',
  inject: 'body',
  filename: 'pages/register/index.html' //输出html文件的位置
 }),
 new DashboardPlugin(),
 new ExtractTextPlugin('css/register/style.css'), //将引入的样式文件单独抽成style.css文件并插入到head标签当中,带有路径时,最后打包
 new webpack.optimize.CommonsChunkPlugin({
  name: 'common',
  filename: 'js/register/common.js',
  minChunks: 3
 })
 ]
}

 const Router = new Route();
 
 Route
 .addRoute({
  path: 'path2',
  viewBox: '.public-container',
  template: require('modules/path2/index.html'),
  pageInit() {
  //webpack提供的分包的API. require.ensure
  require.ensure([], () => {
   let controller = require('modules/path2/controller');
   Router.registerCtrl('path2', new controller('.public-container'));
  }, 'path2');
  }
 })
 .addRoute({
  path: 'path3',
  viewBox: '.public-container',
  template: require('modules/path3/index.html'),
  pageInit() {
  require.ensure([], () => {
   let controller = require('modules/path3/controller');
   Router.registerCtrl('path3', new controller('.public-container'));
  }, 'path3');
  }
 });

 //common.js
 (function(modules) {
 //modules用来保存所有的分包,它是一个数组,数组每个元素对应的都是callback,每个分包都是通过数字来进行标识的
 
 //定义好的全局函数webpackJsonp
 //大家可以看看其他打包好的文件,例如index.js, path2.js和path3.js文件.都是webpackJsonp()这种的形式,大家用过JSONP应该会很好理解。首先在前端定义好函数，然后后端下发组装好的函数js文件,前端获取到这个文件后就可以立即进行执行了
 var parentJsonpFunction = window["webpackJsonp"];
 window["webpackJsonp"] = function webpackJsonpCallback(chunkIds, moreModules) {
  var moduleId, chunkId, i = 0, callbacks = [];
 for(;i < chunkIds.length; i++) {
  chunkId = chunkIds[i];
  if(installedChunks[chunkId])
  callbacks.push.apply(callbacks, installedChunks[chunkId]);
  installedChunks[chunkId] = 0;
 }
  //这个全局函数会将各个分包缓存到modules
 for(moduleId in moreModules) {
  modules[moduleId] = moreModules[moduleId];
 }
 if(parentJsonpFunction) parentJsonpFunction(chunkIds, moreModules);
 while(callbacks.length)
  callbacks.shift().call(null, __webpack_require__);
  //用以启动整个应用
 if(moreModules[0]) {
  installedModules[0] = 0;
  return __webpack_require__(0);
 }
 };
 })([]);

 // The require function
  //通过数字标识的moduleId
 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] = {
  exports: {},
  id: moduleId,
  loaded: false
 };

 // Execute the module function
 modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);

 // Flag the module as loaded
 module.loaded = true;

 // Return the exports of the module
 return module.exports;
 }

 // This file contains only the entry chunk.
 // The chunk loading function for additional chunks
  //异步加载函数
 __webpack_require__.e = function requireEnsure(chunkId, callback) {
 // "0" is the signal for "already loaded"
 if(installedChunks[chunkId] === 0)
  return callback.call(null, __webpack_require__);

 // an array means "currently loading".
 if(installedChunks[chunkId] !== undefined) {
  installedChunks[chunkId].push(callback);
 } else {
   //创建script表情,请求js文件
  // start chunk loading
  installedChunks[chunkId] = [callback];
  var head = document.getElementsByTagName('head')[0];
  var script = document.createElement('script');
  script.type = 'text/javascript';
  script.charset = 'utf-8';
  script.async = true;

  script.src = __webpack_require__.p + "js/register/" + ({"0":"index","1":"path2","2":"path3"}[chunkId]||chunkId) + ".js";
  head.appendChild(script);
 }
 };

 // expose the modules object (__webpack_modules__)
 __webpack_require__.m = modules;

 // expose the module cache
 __webpack_require__.c = installedModules;

 // __webpack_public_path__
  //配置文件中定义的publicPath,build完后加载文件的路径
 __webpack_require__.p = "/static/taxi-driver/";
})

 webpackJsonp([0, 3], [
 /* 0 */
/***/ function(module, exports, __webpack_require__) {

 'use strict';

 __webpack_require__(1);

 __webpack_require__(8);

/***/ },
/* 1 */
/* 2 */
/* 3 */
//....
/* 8 */
 ])

 /* 0 */
 function(module, exports, __webpack_require__) {

 'use strict';

 __webpack_require__(1);

 __webpack_require__(8);

}

 /* 1 */
/***/ function(module, exports, __webpack_require__) {

 'use strict';

 Object.defineProperty(exports, "__esModule", {
 value: true
 });
 
 //加载路由库
 var _index = __webpack_require__(2);
 //实例化一个路由
 var Router = new _index.Route();
 //定义好的路由规则
 Router.home('path2').addRoute({
 path: 'path2',
 viewBox: '.public-container',
 //模板文件,为模块4
 template: __webpack_require__(4),
 pageInit: function pageInit() {
 //这个方法是在common.js中__webpack_require__的静态方法,用来异步加载js。
 //异步加载js的文件（即chunk）用来数字来标识，chunk的顺序从0开始.
 //这里path2.js的chunk num为1,大家可以回过头到common.js的__webpack_require__.e方法里面看看,里面已经做好了chunk num和模块文件的映射, chunk 1对应的模块文件为path2.js,chunk 2对用的模块文件为path3.js
 //__webpack_require__.e()接收的第二个参数为异步加载模块后的回调. 当path2.js被加载完后,在modules里面进行了缓存.这时就可以通过模块id去获取这个模块。然后进行初始化等后续的操作
  __webpack_require__.e/* nsure */(1, function () {
  var controller = __webpack_require__(6);
  Router.registerCtrl('path2', new controller('.public-container'));
  });
 }
 }).addRoute({
 path: 'path3',
 viewBox: '.public-container',
 //模板文件,为模块5
 template: __webpack_require__(5),
 pageInit: function pageInit() {
  __webpack_require__.e/* nsure */(2, function () {
  var controller = __webpack_require__(7);
  Router.registerCtrl('path3', new controller('.public-container'));
  });
 }
 });

 Router.bootstrap();

 exports.default = Router;

/***/ },