Webpack4 性能优化实践

为什么需要性能优化

在使用 Webpack 时，如果不注意性能优化，可能会产生性能问题，会导致在开发体验上不是非常丝滑，性能问题主要是编译速度慢，打包体积过大，因此性能优化也主要从这些方面来分析。本文主要是自己平时的工作积累和参考别人的文章，而进行总结，基于 Webpack4 版本。

构建分析

编译速度分析

对 Webpack 构建速度进行优化的首要任务就是去知道哪些地方值得我们注意。
speed-measure-webpack-plugin 插件能够测量 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
[email protected]@babel-loader took 29.98 secs
  module count = 1503
[email protected]@babel-loader, and
[email protected]@eslint-loader took 18.74 secs
  module count = 86
[email protected]@css-loader, and
[email protected]@less-loader took 16.45 secs
  module count = 64
modules with no loaders took 2.24 secs
  module count = 7
[email protected]@file-loader took 1.03 secs
  module count = 17
[email protected]@style-loader, and
[email protected]@css-loader, and
[email protected]@less-loader took 0.102 secs
  module count = 64
[email protected]@html-webpack-plugin took 0.021 secs
  module count = 1

居然达到了惊人的 38.3 秒，虽然有点不是很准确，但是非常慢。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
});

打包体积分析

通过 webpack-bundle-analyzer 插件能够在 Webpack 构建结束后生成构建产物体积报告，配合可视化的页面，能够直观知道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：

可以看出一个很明显的问题就是 Ant Design、TRTC、Mobx 这些库，没有排除。

打包体积如下：

如何优化

缩小构建目标

• 优化 resolve.modules 配置（减少模块搜索层级和不必要的编译工作）
• 优化 resolve.extensions 配置
• 增加缓存

const path = require('path');
module.exports = {
    resolve: {
        // 自动解析确定的扩展
        extensions: ['.js', '.jsx', '.css', '.less', '.json'],
        alias: {
            // 创建 import 或 require 的别名，来确保模块引入变得更简单
            '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` 中使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'
            }
        ]
    }
};

使用 thread-loader，开启多进程

thread-loader 会将你的 loader 放置在一个 worker 池里面运行，每个 worker 都是一个单独的有 600ms 限制的 node.js 进程。同时跨进程的数据交换也会被限制。请在高开销的 loader 中使用，否则效果不佳。

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

使用 hard-source-webpack-plugin

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

hard-source-webpack-plugin 是 Webpack 的插件，为模块提供中间缓存步骤。为了查看结果，您需要使用此插件运行 Webpack 两次：第一次构建将花费正常的时间。第二次构建将显着加快（大概提升 90% 的构建速度）。不过该插件很久没更新了，不太建议使用。

去掉 eslint-loader

由于我项目中使用了 eslint-loader 如果配置了 precommit，其实可以去掉的。

通过 externals 把相关的包，排除

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

JS 压缩

从 Webpack4 开始，默认情况下使用 terser 压缩生产环境下的输出结果。Terser 是一款兼容 ES2015 + 的 JavaScript 压缩器。与 UglifyJS（许多项目的早期标准）相比，它是面向未来的选择。有一个 UglifyJS 的分支—— uglify-es，但由于它不再维护，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
            })
        ]
    },
};

CSS 压缩

Webpack 4.0 以后，官方推荐使用 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]
            }
        ]
    },
};

FAQ

Ant Design 无法加载

请确保加载顺序，Moment、Polyfill 放在 Ant Design 前面加载

MobX 无法加载

MobX 引入 mobx.umd.min.js 库，mobx-react 需要引入

package.json

{
    "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"
    }
}

最终效果

打包体积：

打包体积由原先 2.1M 变成了 882KB，可以说效果非常巨大。

包依赖：

Ant Design、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
[email protected]@babel-loader took 8.26 secs
  module count = 277
[email protected]@babel-loader, and
[email protected]@eslint-loader took 7.18 secs
  module count = 86
[email protected]@css-loader, and
[email protected]@less-loader took 1.94 secs
  module count = 28
modules with no loaders took 0.728 secs
  module count = 12
[email protected]@file-loader took 0.392 secs
  module count = 17
[email protected]@style-loader, and
[email protected]@css-loader, and
[email protected]@less-loader took 0.052 secs
  module count = 28
[email protected]@html-webpack-plugin took 0.026 secs
  module count = 1

编译速度由原先 38.3 secs（实际编译速度大概 15 秒左右），减少到 10.67 secs（实际编译速度 10 秒左右）。

国内外公共 CDN 地址

• BootCDN
• cdnjs

参考资料

• Webpack Guidebook
• Webpack 核心知识有哪些？

博客

博客