二、webpack进阶 - 05. css代码分割 - 《webpack专题》

一、css代码分割
注意：
- 解决：

一、css代码分割

const { merge } = require('webpack-merge');
const commBase = require('./webpack.base');
const autoprefixer = require('autoprefixer');
const MiniCssExtractPlugin = require('mini-css-extract-plugin')
const webpack_prod = {
  mode: 'production',
  // 开启tree shaking
  devtool: 'cheap-module-source-map',
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
                    // 将css代码通过loader处理放入一个css文件中
          MiniCssExtractPlugin.loader,
          'css-loader',
          {
            loader: 'postcss-loader',
            options: {
              postcssOptions: {
                plugins: [autoprefixer]
              }
            }
          }
        ]
      }
    ]
  },
    // 引入插件
  plugins: [new MiniCssExtractPlugin()]
};
module.exports = merge(commBase, webpack_prod);

const { merge } = require('webpack-merge');
const commBase = require('./webpack.base');
const autoprefixer = require('autoprefixer');
//分割css代码
const MiniCssExtractPlugin = require('mini-css-extract-plugin');
const CssMinimizerPlugin = require('css-minimizer-webpack-plugin');
const webpack_prod = {
  mode: 'production',
  // 开启tree shaking
  devtool: 'cheap-module-source-map',
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          MiniCssExtractPlugin.loader,
          'css-loader',
          {
            loader: 'postcss-loader',
            options: {
              postcssOptions: {
                plugins: [autoprefixer]
              }
            }
          }
        ]
      }
    ]
  },
  optimization: {
    splitChunks: {
      cacheGroups: {
        styles: {
          name: 'styles',
          test: /\.css$/,
          chunks: 'all',
          enforce: true
        }
      }
    },
    minimize: true,
    minimizer: [new CssMinimizerPlugin()]
  },
  plugins: [
    new MiniCssExtractPlugin({
      filename: '[name].css'
    })
  ]
};
module.exports = merge(commBase, webpack_prod);

{
  "name": "01.test",
  "version": "1.0.0",
  "description": "",
  "sideEffects": [
    "*.css"
  ],
  "main": "index.js",
  "scripts": {
    "build": "webpack --config ./build/webpack.prod.js",
    "dev": "webpack-dev-server --config ./build/webpack.dev.js",
    "dev:build": "webpack --config ./build/webpack.dev.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@babel/cli": "^7.18.6",
    "@babel/core": "^7.18.6",
    "@babel/preset-env": "^7.18.6",
    "@babel/preset-react": "^7.18.6",
    "autoprefixer": "^7.0.0",
    "babel-loader": "^8.2.5",
    "clean-webpack-plugin": "^3.0.0",
    "core-js": "^3.23.3",
    "css-loader": "^5.2.7",
    "css-minimizer-webpack-plugin": "^1.3.0",
    "file-loader": "^6.2.0",
    "html-webpack-plugin": "^4.5.2",
    "mini-css-extract-plugin": "^1.6.2",
    "node-sass": "^5.0.0",
    "postcss-loader": "^4.3.0",
    "react": "^18.2.0",
    "react-dom": "^18.2.0",
    "sass-loader": "^10.3.0",
    "style-loader": "^2.0.0",
    "url-loader": "^3.0.0",
    "vue-loader": "^15.6.0",
    "webpack": "^4.46.0",
    "webpack-cli": "^3.3.12",
    "webpack-dev-server": "^3.11.3",
    "webpack-merge": "^5.0.0"
  },
  "dependencies": {
    "@babel/polyfill": "^7.12.1",
    "lodash": "^4.17.21"
  }
}

使用两个插件：

:::info

mini-css-extract-plugin: 将css代码提取出来，放入一个文件中，通过link标签引入
css-minimizer-webpack-plugin: 将代码压缩，合并相同 css 选择器的配置 :::

1.1 MiniCssExtractPlugin插件：
缺点：main.js引入的两个css文件：

:::info 打包生成的**dist**文件夹下的 css 代码（**production**）
没有进行合并，
也没有进行压缩，增大产出代码体积 ::: :::info 通过CssMinimizerPlugin插件可以解决代码合并，压缩代码： ::: 将css代码放入一个文件中：
将模块中的 import 'index.css' 引入的css文件代码，打包到一个css文件中，通过在index.html 中通过 <link href='xx'> 的方式，进行引入
```
"css-minimizer-webpack-plugin": "^1.3.0",
"mini-css-extract-plugin": "^1.6.2",
// 将css代码在production环境中，打包到一个文件中
optimization: {
splitChunks: {
  cacheGroups: {
    styles: {
      name: 'styles',
        test: /\.css$/,
          chunks: 'all',
            enforce: true
    }
  }
},
```
使用插件在production环境打包之后，css引入方式为：<link href="xxx"/>,方式，将css代码打包到一个.css 文件中，在引入页面

1.2 打包后压缩css代码：(CssMinimizerPlugin)
1.2.1 css-minimizer-webpack-plugin
打包时，压缩代码的同时，还会对**css**代码中相同的配置，进行合并

将所有的css文件提取到一个css文件中，改变默认名称的配置