webpack5 splitChunks 配置和用法

前言

CommonsChunkPlugin主要是用来提取第三方库和公共模块，避免首屏加载的bundle文件或者按需加载的bundle文件体积过大，从而导致加载时间过长，着实是优化的一把利器。

先来说一下各种教程以及文档中CommonsChunkPlugin提及到chunk有哪几种，主要有以下三种：

1.webpack当中配置的入口文件（entry）是chunk，可以理解为entry chunk
2.入口文件以及它的依赖文件通过code split（代码分割）出来的也是chunk，可以理解为children chunk
3.通过CommonsChunkPlugin创建出来的文件也是chunk，可以理解为commons chunk

splitChunks优点

• 它不会打包不需要的模块
• 对异步模块有效（默认情况下是打开的）
• 更加容易使用和更加自动化

实践

src目录下文件，如下：

common.js
export const common = '公共文件';

first.js
import {common} from './common';
import $ from 'jquery';
console.log($，`第一个文件，引入公共文件：${common}`);

second.js
import {common} from './common';
import $ from 'jquery';
console.log($，`second ${common}` 
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webpack.config.js：

const path = require("path");
const webpack = require("webpack");

const config = {entry: {first: './src/first.js',second: './src/second.js'},output: {path: path.resolve(__dirname,'./dist'),filename: '[name].js',clean: true},
}

module.exports = config; 
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运行 webpack

asset first.js 324 KiB [emitted] (name: first)
asset second.js 324 KiB [emitted] [compared for emit] (name: second)
runtime modules 1.95 KiB 8 modules
cacheable modules 282 KiB./src/first.js 125 bytes [built] [code generated]./src/second.js 91 bytes [built] [code generated]./src/common.js 37 bytes [built] [code generated]./node_modules/jquery/dist/jquery.js 282 KiB [built] [code generated]
webpack 5.73.0 compiled successfully in 371 ms 
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dist文件下 生成两个文件first.js, second.js first.js看下：

分离出第三方库，自定义的公共模块，webpack运行文件

const path = require("path");
const webpack = require("webpack");

const config = {entry: {first: './src/first.js',second: './src/second.js'},output: {path: path.resolve(__dirname,'./dist'),filename: '[name].js',clean: true},optimization:{splitChunks: { // 选择哪些 chunk 进行优化，可选值：initial(初始块)、async(按需加载块)、all(全部块)，默认为all,chunks: 'all',},}
}
module.exports = config; 
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查看运行情况：

asset vendors-node_modules_jquery_dist_jquery_js.js 320 KiB [emitted] (id hint: vendors)
asset first.js 8.94 KiB [emitted] (name: first)
asset second.js 8.92 KiB [emitted] (name: second)
Entrypoint first 329 KiB = vendors-node_modules_jquery_dist_jquery_js.js 320 KiB first.js 8.94 KiB
Entrypoint second 329 KiB = vendors-node_modules_jquery_dist_jquery_js.js 320 KiB second.js 8.92 KiB
runtime modules 7 KiB 12 modules
cacheable modules 282 KiB./src/first.js 125 bytes [built] [code generated]./src/second.js 91 bytes [built] [code generated]./src/common.js 37 bytes [built] [code generated]./node_modules/jquery/dist/jquery.js 282 KiB [built] [code generated]
webpack 5.73.0 compiled successfully in 371 ms 
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查看dist目录下，新增了一个vendor*.js的文件，把jquery 单独提取出来了

最终代码：

const path = require("path");
const webpack = require("webpack");

const config = {entry: {first: './src/first.js',second: './src/second.js'},output: {path: path.resolve(__dirname,'./dist'),filename: '[name].js',clean: true},optimization:{runtimeChunk: {name: 'runtime'},splitChunks: {cacheGroups: {commons: {name: 'commons', // 设置模块名称，如果不设置就是commons_node_modules_jquery_jquery_src_common_js.jschunks: 'all',minChunks: 2,},},},}
}
module.exports = config; 
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运行结果：

asset commons.js 322 KiB [emitted] (name: commons) (id hint: commons)
asset runtime.js 7.15 KiB [compared for emit] (name: runtime)
asset second.js 1.02 KiB [emitted] (name: second)
asset first.js 1.01 KiB [emitted] (name: first)
Entrypoint first 330 KiB = runtime.js 7.15 KiB commons.js 322 KiB first.js 1.01 KiB
Entrypoint second 330 KiB = runtime.js 7.15 KiB commons.js 322 KiB second.js 1.02 KiB
runtime modules 3.5 KiB 6 modules
cacheable modules 282 KiB./src/first.js 125 bytes [built] [code generated]./src/second.js 91 bytes [built] [code generated]./src/common.js 37 bytes [built] [code generated]./node_modules/jquery/dist/jquery.js 282 KiB [built] [code generated]
webpack 5.73.0 compiled successfully in 350 ms 
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生成文件：