经验总结

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【前端必会】不知道webpack插件? webpack插件源码分析BannerPlugin

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背景

  1. 不知道webpack插件是怎么回事，除了官方的文档外，还有一个很直观的方式，就是看源码 。
  2. 看源码是一个挖宝的行动，也是一次冒险，我们可以找一些代码量不是很大的源码
  3. 比如webpack插件，我们就可以通过BannerPlugin源码，来看下官方是如何实现一个插件的
  4. 希望对各位同学有所帮助，必要时可以通过源码进行一门技术的学习，加深理解
闲言少叙，直接上代码https://github.com/webpack/webpack/blob/main/lib/BannerPlugin.js
配合文档apihttps://webpack.docschina.org/api/compilation-object/#updateasset
代码分析已添加中文注释
/* MIT License http://www.opensource.org/licenses/mit-license.php Author Tobias Koppers @sokra*/"use strict";const { ConcatSource } = require("webpack-sources");const Compilation = require("./Compilation");const ModuleFilenameHelpers = require("./ModuleFilenameHelpers");const Template = require("./Template");const createSchemaValidation = require("./util/create-schema-validation");/** @typedef {import("../declarations/plugins/BannerPlugin").BannerPluginArgument} BannerPluginArgument *//** @typedef {import("../declarations/plugins/BannerPlugin").BannerPluginOptions} BannerPluginOptions *//** @typedef {import("./Compiler")} Compiler */// 创建一个验证const validate = createSchemaValidation(require("../schemas/plugins/BannerPlugin.check.js"),() => require("../schemas/plugins/BannerPlugin.json"),{name: "Banner Plugin",baseDataPath: "options",});//包装Banner文字const wrapComment = (str) => {if (!str.includes("\n")) {return Template.toComment(str);}return `/*!\n * ${str.replace(/\*\//g, "* /").split("\n").join("\n * ").replace(/\s+\n/g, "\n").trimRight()}\n */`;};//插件类class BannerPlugin {/*** @param {BannerPluginArgument} options options object* 初始化插件配置*/constructor(options) {if (typeof options === "string" || typeof options === "function") {options = {banner: options,};}validate(options);this.options = options;const bannerOption = options.banner;if (typeof bannerOption === "function") {const getBanner = bannerOption;this.banner = this.options.raw? getBanner: (data) => wrapComment(getBanner(data));} else {const banner = this.options.raw? bannerOption: wrapComment(bannerOption);this.banner = () => banner;}}/*** Apply the plugin* @param {Compiler} compiler the compiler instance* @returns {void}* 插件主方法*/apply(compiler) {const options = this.options;const banner = this.banner;const matchObject = ModuleFilenameHelpers.matchObject.bind(undefined,options);//创建一个Map，处理如果添加过的文件，不在添加const cache = new WeakMap();compiler.hooks.compilation.tap("BannerPlugin", (compilation) => {//处理Assets的hookcompilation.hooks.processAssets.tap({name: "BannerPlugin",//PROCESS_ASSETS_STAGE_ADDITIONS — 为现有的 asset 添加额外的内容，例如 banner 或初始代码 。stage: Compilation.PROCESS_ASSETS_STAGE_ADDITIONS,},() => {//遍历当前编译对象的chunksfor (const chunk of compilation.chunks) {//如果配置标识只处理入口，但是当前chunk不是入口，直接进入下一次循环if (options.entryOnly && !chunk.canBeInitial()) {continue;}//否则，遍历chunk下的文件for (const file of chunk.files) {//根据配置匹配文件是否满足要求，如果不满足，直接进入下一次循环，处理下一个文件if (!matchObject(file)) {continue;}//否则，const data = https://www.huyubaike.com/biancheng/{chunk,filename: file,};//获取插值路径？https://webpack.docschina.org/api/compilation-object/#getpathconst comment = compilation.getPath(banner, data);//修改Asset，https://webpack.docschina.org/api/compilation-object/#updateassetcompilation.updateAsset(file, (old) => {//从缓存中获取let cached = cache.get(old);//如果缓存不存在 或者缓存的comment 不等于当前的commentif (!cached || cached.comment !== comment) {//源文件追加到头部或者尾部const source = options.footer? new ConcatSource(old,"\n", comment): new ConcatSource(comment, "\n", old);//创建对象加到缓存cache.set(old, { source, comment });//返回修改后的源return source;}//返回缓存中的源return cached.source;});}}});});}}module.exports = BannerPlugin;

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