Plugin 原理 #

// https://github.com/webpack/tapable/blob/master/lib/index.js
exports.SyncHook = require("./SyncHook");
exports.SyncBailHook = require("./SyncBailHook");
exports.SyncWaterfallHook = require("./SyncWaterfallHook");
exports.SyncLoopHook = require("./SyncLoopHook");
exports.AsyncParallelHook = require("./AsyncParallelHook");
exports.AsyncParallelBailHook = require("./AsyncParallelBailHook");
exports.AsyncSeriesHook = require("./AsyncSeriesHook");
exports.AsyncSeriesBailHook = require("./AsyncSeriesBailHook");
exports.AsyncSeriesLoopHook = require("./AsyncSeriesLoopHook");
exports.AsyncSeriesWaterfallHook = require("./AsyncSeriesWaterfallHook");
exports.HookMap = require("./HookMap");
exports.MultiHook = require("./MultiHook");

class TestPlugin {
  constructor() {
    console.log("TestPlugin constructor()");
  }
  // 1. webpack读取配置时，new TestPlugin() ，会执行插件 constructor 方法
  // 2. webpack创建 compiler 对象
  // 3. 遍历所有插件，调用插件的 apply 方法
  apply(compiler) {
    console.log("TestPlugin apply()");
  }
}

module.exports = TestPlugin;

class TestPlugin {
  constructor() {
    console.log("TestPlugin constructor()");
  }
  // 1. webpack读取配置时，new TestPlugin() ，会执行插件 constructor 方法
  // 2. webpack创建 compiler 对象
  // 3. 遍历所有插件，调用插件的 apply 方法
  apply(compiler) {
    console.log("TestPlugin apply()");

    // 从文档可知, compile hook 是 SyncHook, 也就是同步钩子, 只能用tap注册
    compiler.hooks.compile.tap("TestPlugin", (compilationParams) => {
      console.log("compiler.compile()");
    });

    // 从文档可知, make 是 AsyncParallelHook, 也就是异步并行钩子, 特点就是异步任务同时执行
    // 可以使用 tap、tapAsync、tapPromise 注册。
    // 如果使用tap注册的话，进行异步操作是不会等待异步操作执行完成的。
    compiler.hooks.make.tap("TestPlugin", (compilation) => {
      setTimeout(() => {
        console.log("compiler.make() 111");
      }, 2000);
    });

    // 使用tapAsync、tapPromise注册，进行异步操作会等异步操作做完再继续往下执行
    compiler.hooks.make.tapAsync("TestPlugin", (compilation, callback) => {
      setTimeout(() => {
        console.log("compiler.make() 222");
        // 必须调用
        callback();
      }, 1000);
    });

    compiler.hooks.make.tapPromise("TestPlugin", (compilation) => {
      console.log("compiler.make() 333");
      // 必须返回promise
      return new Promise((resolve) => {
        resolve();
      });
    });

    // 从文档可知, emit 是 AsyncSeriesHook, 也就是异步串行钩子，特点就是异步任务顺序执行
    compiler.hooks.emit.tapAsync("TestPlugin", (compilation, callback) => {
      setTimeout(() => {
        console.log("compiler.emit() 111");
        callback();
      }, 3000);
    });

    compiler.hooks.emit.tapAsync("TestPlugin", (compilation, callback) => {
      setTimeout(() => {
        console.log("compiler.emit() 222");
        callback();
      }, 2000);
    });

    compiler.hooks.emit.tapAsync("TestPlugin", (compilation, callback) => {
      setTimeout(() => {
        console.log("compiler.emit() 333");
        callback();
      }, 1000);
    });
  }
}

module.exports = TestPlugin;

// plugins/banner-webpack-plugin.js
class BannerWebpackPlugin {
  constructor(options = {}) {
    this.options = options;
  }

  apply(compiler) {
    // 需要处理文件
    const extensions = ["js", "css"];

    // emit是异步串行钩子
    compiler.hooks.emit.tapAsync("BannerWebpackPlugin", (compilation, callback) => {
      // compilation.assets包含所有即将输出的资源
      // 通过过滤只保留需要处理的文件
      const assetPaths = Object.keys(compilation.assets).filter((path) => {
        const splitted = path.split(".");
        return extensions.includes(splitted[splitted.length - 1]);
      });

      assetPaths.forEach((assetPath) => {
        const asset = compilation.assets[assetPath];

        const source = `/*
* Author: ${this.options.author}
*/\n${asset.source()}`;

        // 覆盖资源
        compilation.assets[assetPath] = {
          // 资源内容
          source() {
            return source;
          },
          // 资源大小
          size() {
            return source.length;
          },
        };
      });

      callback();
    });
  }
}

module.exports = BannerWebpackPlugin;

// plugins/clean-webpack-plugin.js
class CleanWebpackPlugin {
  apply(compiler) {
    // 获取操作文件的对象
    const fs = compiler.outputFileSystem;
    // emit是异步串行钩子
    compiler.hooks.emit.tapAsync("CleanWebpackPlugin", (compilation, callback) => {
      // 获取输出文件目录
      const outputPath = compiler.options.output.path;
      // 删除目录所有文件
      const err = this.removeFiles(fs, outputPath);
      // 执行成功err为undefined，执行失败err就是错误原因
      callback(err);
    });
  }

  removeFiles(fs, path) {
    try {
      // 读取当前目录下所有文件
      const files = fs.readdirSync(path);

      // 遍历文件，删除
      files.forEach((file) => {
        // 获取文件完整路径
        const filePath = `${path}/${file}`;
        // 分析文件
        const fileStat = fs.statSync(filePath);
        // 判断是否是文件夹
        if (fileStat.isDirectory()) {
          // 是文件夹需要递归遍历删除下面所有文件
          this.removeFiles(fs, filePath);
        } else {
          // 不是文件夹就是文件，直接删除
          fs.unlinkSync(filePath);
        }
      });

      // 最后删除当前目录
      fs.rmdirSync(path);
    } catch (e) {
      // 将产生的错误返回出去
      return e;
    }
  }
}

module.exports = CleanWebpackPlugin;

// plugins/analyze-webpack-plugin.js
class AnalyzeWebpackPlugin {
  apply(compiler) {
    // emit是异步串行钩子
    compiler.hooks.emit.tap("AnalyzeWebpackPlugin", (compilation) => {
      // Object.entries将对象变成二维数组。二维数组中第一项值是key，第二项值是value
      const assets = Object.entries(compilation.assets);

      let source = "# 分析打包资源大小 \n| 名称 | 大小 |\n| --- | --- |";

      assets.forEach(([filename, file]) => {
        source += `\n| ${filename} | ${file.size()} |`;
      });

      // 添加资源
      compilation.assets["analyze.md"] = {
        source() {
          return source;
        },
        size() {
          return source.length;
        },
      };
    });
  }
}

module.exports = AnalyzeWebpackPlugin;

// plugins/inline-chunk-webpack-plugin.js
const HtmlWebpackPlugin = require("safe-require")("html-webpack-plugin");

class InlineChunkWebpackPlugin {
  constructor(tests) {
    this.tests = tests;
  }

  apply(compiler) {
    compiler.hooks.compilation.tap("InlineChunkWebpackPlugin", (compilation) => {
      const hooks = HtmlWebpackPlugin.getHooks(compilation);

      hooks.alterAssetTagGroups.tap("InlineChunkWebpackPlugin", (assets) => {
        assets.headTags = this.getInlineTag(assets.headTags, compilation.assets);
        assets.bodyTags = this.getInlineTag(assets.bodyTags, compilation.assets);
      });

      hooks.afterEmit.tap("InlineChunkHtmlPlugin", () => {
        Object.keys(compilation.assets).forEach((assetName) => {
          if (this.tests.some((test) => assetName.match(test))) {
            delete compilation.assets[assetName];
          }
        });
      });
    });
  }

  getInlineTag(tags, assets) {
    return tags.map((tag) => {
      if (tag.tagName !== "script") return tag;

      const scriptName = tag.attributes.src;

      if (!this.tests.some((test) => scriptName.match(test))) return tag;

      return { tagName: "script", innerHTML: assets[scriptName].source(), closeTag: true };
    });
  }
}

module.exports = InlineChunkWebpackPlugin;