652 webpack代码分离：多入口起点，入口依赖，SplitChunks，动态导入，代码懒加载，optimization.chunkIds、runtimeChunk，Prefetch和Preload

认识代码分离

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多入口起点

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Entry Dependencies(入口依赖)

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SplitChunks

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SplitChunks自定义配置

• 当然，我们可以自定义更多配置，我们来了解几个非常关键的属性：

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SplitChunks自定义配置解析

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SplitChunks自定义配置解析

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动态导入(dynamic import)

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动态导入的文件命名

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代码的懒加载

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optimization.chunkIds配置

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optimization. runtimeChunk配置

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Prefetch和Preload

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目录结构

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package.json

{
  "name": "webpack_devserver",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "build": "webpack --config ./config/webpack.common.js --env production",
    "serve": "webpack serve --config ./config/webpack.common.js --env development"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@babel/core": "^7.12.17",
    "@babel/preset-env": "^7.12.17",
    "@babel/preset-react": "^7.12.13",
    "@pmmmwh/react-refresh-webpack-plugin": "^0.4.3",
    "babel-loader": "^8.2.2",
    "clean-webpack-plugin": "^3.0.0",
    "css-loader": "^5.0.2",
    "html-webpack-plugin": "^5.2.0",
    "react-refresh": "^0.9.0",
    "style-loader": "^2.0.0",
    "vue-loader": "^15.9.6",
    "vue-template-compiler": "^2.6.12",
    "webpack": "^5.23.0",
    "webpack-cli": "^4.5.0",
    "webpack-dev-server": "^3.11.2",
    "webpack-merge": "^5.7.3"
  },
  "dependencies": {
    "axios": "^0.21.1",
    "dayjs": "^1.10.4",
    "express": "^4.17.1",
    "lodash": "^4.17.21",
    "react": "^17.0.1",
    "react-dom": "^17.0.1",
    "react-router-dom": "^5.2.0",
    "vue": "^2.6.12",
    "webpack-dev-middleware": "^4.1.0"
  }
}

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webpack.common.js

const resolveApp = require("./paths");
const HtmlWebpackPlugin = require("html-webpack-plugin");
const VueLoaderPlugin = require("vue-loader/lib/plugin");
const TerserPlugin = require("terser-webpack-plugin");

const { merge } = require("webpack-merge");

const prodConfig = require("./webpack.prod");
const devConfig = require("./webpack.dev");

const commonConfig = {
  entry: {
    // 【多入口】
    main: "./src/main.js",
    index: "./src/index.js"
    // main: { import: "./src/main.js", dependOn: "shared" },
    // index: { import: "./src/index.js", dependOn: "shared" },
    // lodash: "lodash",
    // dayjs: "dayjs"
    // shared: ["lodash", "dayjs"]
  },
  output: {
    path: resolveApp("./build"),
    filename: "[name].bundle.js", // 【[name]是entry中的key。】
    chunkFilename: "[name].[hash:6].chunk.js" // 动态导入的文件命名
  },
  resolve: {
    extensions: [".wasm", ".mjs", ".js", ".json", ".jsx", ".ts", ".vue"],
    alias: {
      "@": resolveApp("./src"),
      pages: resolveApp("./src/pages"),
    },
  },
  optimization: {
    // 对代码进行压缩相关的操作
    minimizer: [
      new TerserPlugin({
        extractComments: false,
      }),
    ],
    // natural: 使用自然数(不推荐),
    // named: 使用包所在目录作为name(在开发环境推荐)
    // deterministic: 生成id, 针对相同文件生成的id是不变
    // chunkIds: "deterministic",
    // 【splitChunks：webpack会自动配置开发环境和生产换的值】
    splitChunks: {
      // async：异步导入， initial：同步导入， all：异步/同步导入
      chunks: "all",
      // 最小尺寸: 单位是字节，如果拆分出来一个, 那么拆分出来的这个包的大小最小为minSize
      minSize: 20000,
      // 将大于maxSize的包, 拆分成不小于minSize的包
      maxSize: 20000,
      // minChunks表示引入的包, 至少被导入了几次 【才拆分】
      minChunks: 1,
      cacheGroups: {
        // 【vendor：供应商。所有第三方的东西匹配到了后，打包到vendor里，不是必须叫vendor，可以自定义】
        vendor: {
          test: /[\/]node_modules[\/]/, // 这里是路径，匹配windows、mac平台
          filename: "[id]_vendors.js",
          // name: "vendor-chunks.js",
          priority: -10 // 优先级，都是写负数
        },
        // bar: {
        //   test: /bar_/, // 这里是文件，不是路径
        //   filename: "[id]_bar.js"
        // }
        default: {
          // 如果一个文件被引入了2次，就单独打包出来一个js文件
          minChunks: 2,
          filename: "common_[id].js",
          priority: -20
        }
      }
    },
    // true/multiple
    // single
    // object: name
    runtimeChunk: {
      name: function(entrypoint) {
        return `why-${entrypoint.name}`
      }
    }
  },
  module: {
    rules: [
      {
        test: /.jsx?$/i,
        use: "babel-loader",
      },
      {
        test: /.vue$/i,
        use: "vue-loader",
      },
      {
        test: /.css/i,
        use: ["style-loader", "css-loader"],
      },
    ],
  },
  plugins: [
    new HtmlWebpackPlugin({
      template: "./index.html",
    }),
    new VueLoaderPlugin(),
  ],
};

module.exports = function(env) {
  const isProduction = env.production;
  process.env.NODE_ENV = isProduction ? "production" : "development";

  const config = isProduction ? prodConfig : devConfig;
  const mergeConfig = merge(commonConfig, config);

  return mergeConfig;
};

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main.js

import _ from 'lodash';
import dayjs from 'dayjs';

import "./bar_01";
import "./bar_02";

console.log("Hello Main");
console.log(_.join(["Hello", "Main"]));
console.log(dayjs(), "Main");

// 只要是异步导入的代码, webpack都会进行代码分离
// magic comments
import(/* webpackChunkName: "foo" */"./foo").then(res => {
  console.log(res);
});

import(/* webpackChunkName: "foo_02" */"./foo_02").then(res => {
  console.log(res);
});

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index.js

// import _ from 'lodash';
// import dayjs from 'dayjs';

import "./bar_01";

console.log("Hello Index");

const button = document.createElement("button");
button.innerHTML = "加载元素";

button.addEventListener("click", () => {
  // prefetch -> 魔法注释(magic comments)
  /* webpackPrefetch: true */
  /* webpackPreload: true */
  import(
    /* webpackChunkName: 'element' */
    /* webpackPrefetch: true */
    "./element"
  ).then(({ default: element }) => {
    document.body.appendChild(element);
  })
});
document.body.appendChild(button);

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babel.config.js

const presets = [
  ["@babel/preset-env"],
  ["@babel/preset-react"],
];

const plugins = [];
const isProduction = process.env.NODE_ENV === "production";

// React HMR -> 模块的热替换 必然是在开发时才有效果
if (!isProduction) {
  plugins.push(["react-refresh/babel"]);
} else {

}

module.exports = {
  presets,
  plugins
}

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