关于前端:Webpack4性能优化实践

在应用 Webpack 时，如果不留神性能优化，可能会产生性能问题，会导致在开发体验上不是十分丝滑，性能问题次要是编译速度慢，打包体积过大，因而性能优化也次要从这些方面来剖析。本文次要是本人平时的工作积攒和参考他人的文章，而进行总结，基于 Webpack4 版本。

对 Webpack 构建速度进行优化的首要任务就是去晓得哪些地方值得咱们留神。
speed-measure-webpack-plugin 插件可能测量 Webpack 构建速度

 SMP  ⏱  
General output time took 38.3 secs

 SMP  ⏱  Plugins
HtmlWebpackPlugin took 1.31 secs
CopyPlugin took 0.016 secs
OptimizeCssAssetsWebpackPlugin took 0.002 secs
ContextReplacementPlugin took 0.001 secs
MiniCssExtractPlugin took 0 secs
DefinePlugin took 0 secs

 SMP  ⏱  Loaders
_babel-loader@8.1.0@babel-loader took 29.98 secs
  module count = 1503
_babel-loader@8.1.0@babel-loader, and 
_eslint-loader@3.0.4@eslint-loader took 18.74 secs
  module count = 86
_css-loader@3.6.0@css-loader, and 
_less-loader@5.0.0@less-loader took 16.45 secs
  module count = 64
modules with no loaders took 2.24 secs
  module count = 7
_file-loader@5.1.0@file-loader took 1.03 secs
  module count = 17
_style-loader@1.3.0@style-loader, and 
_css-loader@3.6.0@css-loader, and 
_less-loader@5.0.0@less-loader took 0.102 secs
  module count = 64
_html-webpack-plugin@3.2.0@html-webpack-plugin took 0.021 secs
  module count = 1

竟然达到了惊人的 38.3 秒，尽管有点不是很精确，然而十分慢。发现 babel-loader、eslint-loader、css-loader、less-loader 占据了大头。

const webpackBase = require('./webpack.base.conf');
const path = require('path');

const SpeedMeasureWebpackPlugin = require('speed-measure-webpack-plugin');
const smp = new SpeedMeasureWebpackPlugin();

module.exports = smp.wrap({
    // 配置源码显示方式
    devtool: 'eval-source-map',
    mode: 'development',
    entry: {app: ['./src/index.jsx']
    },
    output: {path: path.resolve(__dirname, 'dist'),
        filename: 'index.js'
    },
    resolve: webpackBase.resolve,
    module: webpackBase.module,
    stats: webpackBase.stats,
    optimization: webpackBase.optimization,
    plugins: [
        webpackBase.plugins.html,
        webpackBase.plugins.miniCssExtract,
        webpackBase.plugins.optimizeCssAssets,
        // webpackBase.plugins.progressBarPlugin,
        webpackBase.plugins.ContextReplacementPlugin,
        webpackBase.plugins.DefinePlugin,
        // webpackBase.plugins.AntdDayjsWebpackPlugin,
        webpackBase.plugins.CopyPlugin
        // webpackBase.plugins.HotModuleReplacementPlugin
    ],
    devServer: webpackBase.devServer,
    watchOptions: webpackBase.watchOptions,
    externals: webpackBase.externals
});

通过 webpack-bundle-analyzer 插件可能在 Webpack 构建完结后生成构建产物体积报告，配合可视化的页面，可能直观晓得产物中的具体占用体积。

const BundleAnalyzerPlugin = require('webpack-bundle-analyzer').BundleAnalyzerPlugin;
module.exports = {plugins: bundleAnalyzer: new BundleAnalyzerPlugin({ analyzerPort: 8081})],
};

效果图如下：

能够看出一个很显著的问题就是 ant、trtc、mobx 这些库，没有排除。

打包体积如下：

优化 resolve.modules 配置（缩小模块搜寻层级和不必要的编译工作）
优化 resolve.extensions 配置
减少缓存

const path = require('path');
module.exports = {
    resolve: {
        // 主动解析确定的扩大
        extensions: ['.js', '.jsx', '.css', '.less', '.json'],
        alias: {
            // 创立 import 或 require 的别名，来确保模块引入变得更简略
            'react': path.resolve(__dirname ,'./node_modules/react/dist/react.min.js')
        },
        // 当从 npm 包导入模块时，此选项将决定在 `package.json` 中应用哪个字段导入模块
        // 默认值为 browser -> module -> main
        mainFields: ['main']
    },
    module: {
        rules: [
            {
                // 排除 node_modules 模块
                test: /\.(js|jsx)$/,
                exclude: /node_modules/,
                // 开启缓存
                loader: 'babel-loader?cacheDirectory=true'
            }
        ]
    }
};

thread-loader 会将你的 loader 搁置在一个 worker 池外面运行，每个 worker 都是一个独自的有 600ms 限度的 node.js 过程。同时跨过程的数据交换也会被限度。请在高开销的 loader 中应用，否则成果不佳。

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        include: path.resolve('src'),
        use: [
          'thread-loader',
          // your expensive loader (e.g babel-loader)
        ],
      },
    ],
  },
};

在 Webpack4 中，hard-source-webpack-plugin 是 DLL 的更好替代者。

hard-source-webpack-plugin 是 Webpack 的插件，为模块提供两头缓存步骤。为了查看后果，您须要应用此插件运行 Webpack 两次：第一次构建将破费失常的工夫。第二次构建将显着放慢（大略晋升 90% 的构建速度）。不过该插件很久没更新了，不太倡议应用。

因为我我的项目中应用了 eslint-loader 如果配置了 precommit，其实能够去掉的。

Webpack

module.exports = {
    // externals 排除对应的包，注：排除掉的包必须要用 script 标签引入下
    externals: {
        react: 'React',
        'react-dom': 'ReactDOM',
        'trtc-js-sdk': 'TRTC',
        bizcharts: 'BizCharts',
        antd: 'antd',
        mobx: 'mobx',
        'mobx-react': 'mobxReact'
    }
};

index.html

<!DOCTYPE html>
<html lang="zh">
    <head>
        <meta charset="utf-8" />
        <meta
            name="viewport"
            content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=0"
        />
        <meta name="baidu-site-verification" content="ptk9VJudKz" />
        <link
            rel="stylesheet"
            href="https://xxx/antd.min3.26.20.css"
        />
        <title>webpack</title>
        <script
            type="text/javascript"
            src="https://xxx/17.0.0react.production.min.js"
        ></script>
        <script
            type="text/javascript"
            src="https://xxx/17.0.0react-dom.production.min.js"
        ></script>
        <script
            type="text/javascript"
            src="https://xxx/BizCharts3.5.8.js"
        ></script>
        <script
            type="text/javascript"
            src="https://xxx/trtc4.6.7.js"
        ></script>
        <script
            type="text/javascript"
            src="https://xxx/moment2.29.1.min.js"
        ></script>
        <script
            type="text/javascript"
            src="https://xxx/moment2.29.1zh-cn.js"
        ></script>
        <script
            type="text/javascript"
            src="https://xxx/polyfill.min7.8.0.js"
        ></script>
        <script
            type="text/javascript"
            src="https://xxx/antd.min3.26.20.js"
        ></script>
        <script
            type="text/javascript"
            src="https://xxx/mobx.umd.min5.13.1.js"
        ></script>
        <script
            type="text/javascript"
            src="https://xxx/mobx-react.index.min5.4.4.js"
        ></script>
    </head>
    <body>
        <div id="root"></div>
    </body>
</html>

从 Webpack4 开始，默认状况下应用 terser 压缩生产环境下的输入后果。Terser 是一款兼容 ES2015 + 的 JavaScript 压缩器。与 UglifyJS（许多我的项目的晚期规范）相比，它是面向未来的抉择。有一个 UglifyJS 的分支—— uglify-es，但因为它不再保护，于是就从这个分支诞生出了一个独立分支，它就是 terser。

const TerserPlugin = require('terser-webpack-plugin');

module.exports = {
    optimization: {
        minimizer: [
            // 压缩 js
            new TerserPlugin({test: /\.(jsx|js)$/,
                extractComments: true,
                parallel: true,
                cache: true
            })
        ]
    },
};

Webpack 4.0 当前，官网举荐应用 mini-css-extract-plugin 插件来打包 CSS 文件。

const MiniCssExtractPlugin = require('mini-css-extract-plugin');

module.exports = {
    module: {
        rules: [
            {test: /\.(css|less)$/,
                use: [MiniCssExtractPlugin.loader]
            }
        ]
    },
};

请确保加载程序，moment、polyfill 放在 ant 后面加载

mobx 引入 mobx.umd.min.js 库，mobx-react 须要引入

{
    "name": "webpack",
    "version": "1.0.0",
    "private": true,
    "main": "index.js",
    "dependencies": {
        "antd": "^3.26.20",
        "babel-eslint": "^10.0.3",
        "babel-loader": "^8.0.0",
        "babel-plugin-import": "^1.13.0",
        "babel-plugin-react-css-modules": "^5.2.6",
        "bizcharts": "^3.5.8",
        "china-division": "^2.3.1",
        "compression-webpack-plugin": "^3.0.1",
        "copy-webpack-plugin": "^5.1.1",
        "css-loader": "^3.2.0",
        "eslint": "^6.8.0",
        "eslint-config-prettier": "^6.11.0",
        "eslint-config-standard": "^14.1.0",
        "eslint-loader": "^3.0.4",
        "eslint-plugin-import": "^2.20.0",
        "eslint-plugin-promise": "^4.2.1",
        "eslint-plugin-react": "^7.17.0",
        "eslint-plugin-standard": "^4.0.1",
        "html-webpack-plugin": "^3.2.0",
        "less": "^3.8.1",
        "less-loader": "^5.0.0",
        "lint-staged": "^10.0.8",
        "mini-css-extract-plugin": "^0.8.0",
        "mobx": "^5.13.1",
        "mobx-react": "^5.4.4",
        "optimize-css-assets-webpack-plugin": "^5.0.1",
        "pre-commit": "^1.2.2",
        "progress-bar-webpack-plugin": "^1.12.1",
        "react": "^17.0.0",
        "react-dom": "^17.0.0",
        "speed-measure-webpack-plugin": "^1.3.1",
        "style-loader": "^1.2.1",
        "terser-webpack-plugin": "^2.2.1",
        "trtc-js-sdk": "^4.6.7",
        "viewerjs": "^1.5.0",
        "webpack": "^4.41.2",
        "webpack-bundle-analyzer": "^3.6.0",
        "webpack-cli": "^3.3.10",
        "webpack-dev-server": "^3.10.1"
    }
}

打包体积：

打包体积由原先 2.1M 变成了 882KB，能够说成果十分微小。

包依赖：

ant、trtc、mobx 这些库也没了

编译速度：

SMP  ⏱  
General output time took 10.67 secs

 SMP  ⏱  Plugins
HtmlWebpackPlugin took 1.69 secs
BundleAnalyzerPlugin took 0.091 secs
CopyPlugin took 0.011 secs
MiniCssExtractPlugin took 0.003 secs
OptimizeCssAssetsWebpackPlugin took 0.002 secs
DefinePlugin took 0.001 secs
ContextReplacementPlugin took 0 secs

 SMP  ⏱  Loaders
_babel-loader@8.1.0@babel-loader took 8.26 secs
  module count = 277
_babel-loader@8.1.0@babel-loader, and 
_eslint-loader@3.0.4@eslint-loader took 7.18 secs
  module count = 86
_css-loader@3.6.0@css-loader, and 
_less-loader@5.0.0@less-loader took 1.94 secs
  module count = 28
modules with no loaders took 0.728 secs
  module count = 12
_file-loader@5.1.0@file-loader took 0.392 secs
  module count = 17
_style-loader@1.3.0@style-loader, and 
_css-loader@3.6.0@css-loader, and 
_less-loader@5.0.0@less-loader took 0.052 secs
  module count = 28
_html-webpack-plugin@3.2.0@html-webpack-plugin took 0.026 secs
  module count = 1

编译速度由原先 38.3 secs（理论编译速度大略 15 秒左右），缩小到 10.67 secs（理论编译速度 10 秒左右）。

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关于前端:Webpack4性能优化实践

为什么须要性能优化

构建剖析

编译速度剖析

打包体积剖析

如何优化

放大构建指标

应用 thread-loader，开启多过程

应用 hard-source-webpack-plugin

去掉 eslint-loader

通过 externals 把相干的包，排除

JS 压缩

CSS 压缩

FAQ

ant 无奈加载

mobx 无奈加载

package.json

最终成果

国内外公共 CDN 地址

参考文献

博客