webpack打包首页如何优化及路由懒加载？本文详解

前言

最近做了一个小型的vue的h5项目，发现在手机上运行的时候，第一次进去的首页比较慢，然后同事提了下可以在生产环境用cdn，于是我尝试了下

生产环境开启cdn

1、在vue.congfig.js里面加入

const isProduction = process.env.NODE_ENV == "production"; configureWebpack: (config) => { if (isProduction) { config.externals = { vue: "Vue", "vue-router": "VueRouter", vant: "vant", _: "lodash", }; 另外注意：光理论是不够的。在此赠送2020最新企业级 Vue3.0/Js/ES6/TS/React/node等实战视频教程，想学的可进裙 519293536 免费获取，小白勿进哦！

externals是让里面的库不被webapck打包，也不影响通过import（或者其他AMD、CMD等）方式引入

2、在index.html引入cdn资源

  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/vant@2.8/lib/index.css" /> <script src="https://cdn.jsdelivr.net/npm/vue@2.6.11"></script> <script src="https://unpkg.com/vue-router/dist/vue-router.js"></script> <script src="https://cdn.jsdelivr.net/npm/vant@2.8/lib/vant.min.js"></script> <script src="https://cdn.bootcdn.net/ajax/libs/lodash.js/4.17.15/lodash.core.min.js"></script> 复制代码

3、优化下写法

// vue.config.js

const cdn = {
  css: ["https://cdn.jsdelivr.net/npm/vant@2.8/lib/index.css"], js: [ "https://cdn.jsdelivr.net/npm/vue@2.6.11", "https://unpkg.com/vue-router/dist/vue-router.js", "https://cdn.jsdelivr.net/npm/vant@2.8/lib/vant.min.js", "https://cdn.bootcdn.net/ajax/libs/lodash.js/4.17.15/lodash.core.min.js", ], }; chainWebpack: (config) => { if (isProduction) { config.plugin("html").tap((args) => { args[0].cdn = cdn; return args; }); } } // index.html <% for(var i in htmlWebpackPlugin.options.cdn && htmlWebpackPlugin.options.cdn.css){%> <link src="<%= htmlWebpackPlugin.options.cdn.css[i] %>"></link> <%}%> <% for(var i in htmlWebpackPlugin.options.cdn && htmlWebpackPlugin.options.cdn.js){%> <script src="<%= htmlWebpackPlugin.options.cdn.js[i] %>"></script> <%}%> 复制代码

优化前

优化后

开启gzip压缩


cnpm install compression-webpack-plugin --save-dev 

// vue.config.js
const CompressionPlugin = require("compression-webpack-plugin"); configureWebpack: (config) => { if (isProduction) { config.externals = { vue: "Vue", "vue-router": "VueRouter", vant: "vant", _: "lodash", }; config.plugins.push( new CompressionPlugin({ algorithm: "gzip", }) ); } }, 复制代码

路由懒加载

  {
    path: "/index", name: "index", component: () => import("../views/index.vue"), meta: { keepAlive: false, }, }, 复制代码

平常当中经常这么写，只不过你可能不知道这就是路由懒加载。官网，官网上提到这是由于异步组件和weback的代码分割code-splitting功能，每个异步路由会打包成不同的块，实现按需加载。除了上面的ES2015模块的写法，它还有

 {
    path: "/index", name: "index", component: (resolve) => require(["../views/index.vue"], resolve), meta: { keepAlive: false, }, }, 复制代码

根据官网提到的，首先创建一个返回Promise的工厂函数

const Index = () => Promise.resolve({ /* 组件定义对象 */ })
复制代码

然后用动态 import语法定义代码分块的分割点

import ('./Index') 复制代码

两者结合，就可以自动分割代码

const Index = () => import('../views/index.vue') 复制代码

先看了下这个code-split，

然后去看了下vue-cli的具体配置，路由已经是Dynamic Import，如上图第二点提到. 下面说说针对于chunk-vendors的分割，正如上图第三点提到，配置splitChunks是了重复数据删除和分割chunks

optimization(开发和生产都是一样的)

optimization:{
      splitChunks: {
        cacheGroups: {  // 缓存组，可以定义多个
          vendors: {     //创建一个 自定义的vendor的chunk
            name: "chunk-vendors", test: /[\\\/]node_modules[\\\/]/, // 匹配node_modules priority: -10, // 理解为缓存的级别 chunks: "initial", }, common: { name: "chunk-common", minChunks: 2, // 分割之前必须共享模块的最小chunk数 priority: -20, chunks: "initial", reuseExistingChunk: true, // 是否复用存在的块 }, }, } } 复制代码

cacheGroups 缓存组，可以定义多个

 cacheGroups: {
        defaultVendors: {
          test: /[\\/]node_modules[\\/]/, priority: -10 }, default: { minChunks: 2, priority: -20, reuseExistingChunk: true } } 复制代码

priority 缓存组的级别

A module can belong to multiple cache groups. The optimization will prefer the cache group with a higher priority. The default groups have a negative priority to allow custom groups to take higher priority (default value is 0 for custom groups)

翻译过来大概就是一个模块可以有多个cash groups，optimization将会选择优先级更高的cash group, default group 的优先级为负数，可以允许custom group有更高的优先级（默认值是0）。简而言之，custom group可以通过priority比default group高

reuseExistingChunk 是否复用存在的块

`output`配置有些不同

// 生产
  output: {
    path:"/dist", filename: "static/js/[name].[contenthash:8].js", publicPath: "/", chunkFilename: "static/js/[name].[contenthash:8].js", // 生成一个8位的hash值 } // 开发 output: { path:"/dist", filename: "static/js/[name].js", publicPath: "/", chunkFilename: "static/js/[name].js", } 复制代码

运行打包

生产输出了css,而开发环境没有,估计是生产配置了这句

  // 生产
    new MiniCssExtractPlugin({
      filename: "static/css/[name].[contenthash:8].css", chunkFilename: "static/css/[name].[contenthash:8].css", }) 复制代码

那么问题来了

开发模式打包出来文件的css到底怎么引入的
打包出来的dist的index.html的link和script标签引入的文件为何不同
preload 和 prefetch的区别

// development
<!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"> <link rel="icon" href="/favicon.ico"> <title>南蓝</title> <link href="/static/js/0.js" rel="prefetch"><link href="/static/js/1.js" rel="prefetch"><link href="/static/js/2.js" rel="prefetch"> <link href="/static/js/3.js" rel="prefetch"> <link href="/static/js/app.js" rel="preload" as="script"> <link href="/static/js/chunk-vendors.js" rel="preload" as="script"> </head> <body> <noscript> <strong>We're sorry but f2e-client doesn't work properly without JavaScript enabled. Please enable it to continue.</strong> </noscript> <div id="app"></div> <script type="text/javascript" src="/static/js/chunk-vendors.js"></script><script type="text/javascript" src="/static/js/app.js"></script></body> </html> 复制代码

再来看看生产打包出来的index.html(production)

// production
<!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"> <link rel=icon href=/favicon.ico> <title>鸭嘴兽</title> <script src=https://cdn.jsdelivr.net/npm/vant@2.8/lib/index.css></script> <script src=https://cdn.jsdelivr.net/npm/vue@2.6.11></script> <script src=https://unpkg.com/vue-router/dist/vue-router.js></script> <script src=https://cdn.jsdelivr.net/npm/vant@2.8/lib/vant.min.js></script> <script src=https://cdn.bootcdn.net/ajax/libs/lodash.js/4.17.15/lodash.core.min.js></script> <link href=/static/css/chunk-0c3564fc.b3594289.css rel=prefetch> <link href=/static/css/chunk-56255d30.c1e34d24.css rel=prefetch> <link href=/static/css/chunk-5ba5813d.a56f098f.css rel=prefetch> <link href=/static/css/chunk-9945b478.66fcd057.css rel=prefetch> <link href=/static/js/chunk-0c3564fc.9d02dfcc.js rel=prefetch> <link href=/static/js/chunk-56255d30.d0115acd.js rel=prefetch> <link href=/static/js/chunk-5ba5813d.10f75234.js rel=prefetch> <link href=/static/js/chunk-9945b478.dc8a4502.js rel=prefetch> <link href=/static/css/app.faa29057.css rel=preload as=style> <link href=/static/css/chunk-vendors.97c56160.css rel=preload as=style> <link href=/static/js/app.5deb2d45.js rel=preload as=script> <link href=/static/js/chunk-vendors.158e0179.js rel=preload as=script> <link href=/static/css/chunk-vendors.97c56160.css rel=stylesheet> <link href=/static/css/app.faa29057.css rel=stylesheet> </head> <body> <noscript><strong>We're sorry but f2e-client doesn't work properly without JavaScript enabled. Please enable it to continue.</strong></noscript> <div id=app></div> <script src=/static/js/chunk-vendors.158e0179.js></script> <script src=/static/js/app.5deb2d45.js></script> </body> </html> 复制代码

为啥有些js用link标签引入，有些用scipt标签引入
link的as属性为啥有时有时无

弹出vue-cli配置webpack设置

开发换环境 npx vue-cli-service inspect --mode development  webpack.config.development.js
生产环境：npx vue-cli-service inspect --mode production  webpack.config.production.js
复制代码

不管前端轮子怎么变化，万变不离其宗，这个宗指的就是html、css、js，所有要回归本质上去,我提出的那些问题，希望下次出篇文章弄懂它，有错误或者有建议可以提出来
最后注意：光理论是不够的。在此赠送2020最新企业级 Vue3.0/Js/ES6/TS/React/node等实战视频教程，想学的可进裙 519293536 免费获取，小白勿进哦！

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