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class="docItemContainer_vinB"><article><nav class="theme-doc-breadcrumbs breadcrumbsContainer_Xlws" aria-label="breadcrumbs"><ul class="breadcrumbs" itemscope="" itemtype="https://schema.org/BreadcrumbList"><li class="breadcrumbs__item"><a class="breadcrumbs__link" href="/awesome-interview/">🏠</a></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item"><span class="breadcrumbs__link" itemprop="item name">模拟题一</span><meta itemprop="position" content="1"></li><li itemscope="" itemprop="itemListElement" itemtype="https://schema.org/ListItem" class="breadcrumbs__item breadcrumbs__item--active"><span class="breadcrumbs__link" itemprop="item name">工程化：webpack 工作流程</span><meta itemprop="position" content="2"></li></ul></nav><div class="tocCollapsible_jdIR theme-doc-toc-mobile tocMobile_TmEX"><button type="button" class="clean-btn tocCollapsibleButton_Fzxq">On this page</button></div><div class="theme-doc-markdown markdown"><h1>webpack 工作流程</h1><blockquote><p>本篇内容和配置基于 webpack v5.52.1 讲解</p></blockquote><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="相关问题">相关问题<a class="hash-link" href="#相关问题" title="Direct link to heading"></a></h2><ul><li>webpack 工作流程是怎样的</li><li>webpack 在不同阶段做了什么事情</li></ul><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="回答关键点">回答关键点<a class="hash-link" href="#回答关键点" title="Direct link to heading"></a></h2><p><code>模块化</code> <code>打包</code> <code>依赖生成</code> <code>工程化</code></p><p>webpack 是一种模块打包工具，可以将各类型的资源，例如图片、CSS、JS 等，转译组合为 JS 格式的 bundle 文件。</p><p><img loading="lazy" src="https://user-images.githubusercontent.com/15681693/132979267-8ec79dc5-5249-4d2c-9843-7efa909d7320.png" alt="webpack" class="img_E7b_"></p><blockquote><p>图片来源 <a href="https://webpack.js.org/" target="_blank" rel="noopener noreferrer">webpack 官网</a></p></blockquote><p>webpack 构建的核心任务是完成内容转化和资源合并。主要包含以下 3 个阶段：</p><ol><li>初始化阶段<ul><li><strong>初始化参数</strong>：从配置文件、配置对象和 Shell 参数中读取并与默认参数进行合并，组合成最终使用的参数。</li><li><strong>创建编译对象</strong>：用上一步得到的参数创建 Compiler 对象。</li><li><strong>初始化编译环境</strong>：包括注入内置插件、注册各种模块工厂、初始化 RuleSet 集合、加载配置的插件等。</li></ul></li><li>构建阶段<ul><li><strong>开始编译</strong>：执行 Compiler 对象的 run 方法，创建 Compilation 对象。</li><li><strong>确认编译入口</strong>：进入 entryOption 阶段，读取配置的 Entries，递归遍历所有的入口文件，调用 Compilation.addEntry 将入口文件转换为 Dependency 对象。</li><li><strong>编译模块（make）</strong>： 调用 normalModule 中的 build 开启构建，从 entry 文件开始，调用 loader 对模块进行转译处理，然后调用 JS 解释器（<a href="https://www.npmjs.com/package/acorn" target="_blank" rel="noopener noreferrer">acorn</a>）将内容转化为 AST 对象，然后递归分析依赖，依次处理全部文件。</li><li><strong>完成模块编译</strong>：在上一步处理好所有模块后，得到模块编译产物和依赖关系图。</li></ul></li><li>生成阶段<ul><li><strong>输出资源（seal）</strong>：根据入口和模块之间的依赖关系，组装成多个包含多个模块的 Chunk，再把每个 Chunk 转换成一个 Asset 加入到输出列表，这步是可以修改输出内容的最后机会。</li><li><strong>写入文件系统（emitAssets）</strong>：确定好输出内容后，根据配置的 output 将内容写入文件系统。</li></ul></li></ol><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="知识点深入">知识点深入<a class="hash-link" href="#知识点深入" title="Direct link to heading"></a></h2><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="1-webpack-初始化过程">1. webpack 初始化过程<a class="hash-link" href="#1-webpack-初始化过程" title="Direct link to heading"></a></h3><p>从 webpack 项目 webpack.js 文件 webpack 方法出发，可以看到初始化过程如下：
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<img loading="lazy" src="https://user-images.githubusercontent.com/15681693/138093156-3b4b60be-4bab-4dcb-970d-c83e4ba1dcf6.png" alt="webpack 初始化流程图" class="img_E7b_"></p><ol><li>将命令行参数和用户的配置文件进行合并。</li><li>调用 getValidateSchema 对配置进行校验。</li><li>调用 createCompiler 创建 Compiler 对象。<ol><li>将用户配置和默认配置进行合并处理。</li><li>实例化 Compiler。</li><li>实例化 NodeEnvironmentPlugin。</li><li>处理用户配置的 plugins，执行 plugin 的 apply 方法。</li><li>触发 environment 和 afterEnvironment 上注册的事件。</li><li>注册 webpack 内部插件。</li><li>触发 initialize 事件。</li></ol></li></ol><div class="codeBlockContainer_I0IT language-javascript theme-code-block"><div class="codeBlockContent_wNvx" style="color:#393A34;background-color:#f6f8fa"><pre tabindex="0" class="prism-code language-javascript codeBlock_jd64 thin-scrollbar"><code class="codeBlockLines_mRuA"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">// lib/webpack.js 122 行 部分代码省略处理</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> </span><span class="token function-variable function" style="color:#d73a49">create</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token operator" style="color:#393A34">!</span><span class="token function" style="color:#d73a49">webpackOptionsSchemaCheck</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">options</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 校验参数</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">getValidateSchema</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">webpackOptionsSchema</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> options</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 创建 compiler 对象</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> compiler </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">createCompiler</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">webpackOptions</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">// lib/webpack.js 57 行</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> </span><span class="token function-variable function" style="color:#d73a49">createCompiler</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">rawOptions</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 统一合并处理参数</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> options </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">getNormalizedWebpackOptions</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">rawOptions</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">applyWebpackOptionsBaseDefaults</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">options</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 实例化 compiler</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> compiler </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">new</span><span class="token plain"> </span><span class="token class-name">Compiler</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">options</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">context</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 把 options 挂载到对象上</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> compiler</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">options</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> options</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// NodeEnvironmentPlugin 是对 fs 模块的封装，用来处理文件输入输出等</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">new</span><span class="token plain"> </span><span class="token class-name">NodeEnvironmentPlugin</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">infrastructureLogging</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> options</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">infrastructureLogging</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">apply</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">compiler</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 注册用户配置插件</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token known-class-name class-name">Array</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">isArray</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">options</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">plugins</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">for</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> plugin </span><span class="token keyword" style="color:#00009f">of</span><span class="token plain"> options</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">plugins</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">typeof</span><span class="token plain"> plugin </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"function"</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> plugin</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">call</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">compiler</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> compiler</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">else</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> plugin</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">apply</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">compiler</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">applyWebpackOptionsDefaults</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">options</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 触发 environment 和 afterEnvironment 上注册的事件</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> compiler</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">hooks</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">environment</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">call</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> compiler</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">hooks</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">afterEnvironment</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">call</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 注册 webpack 内置插件</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">new</span><span class="token plain"> </span><span class="token class-name">WebpackOptionsApply</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">process</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">options</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> compiler</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> compiler</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">hooks</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">initialize</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">call</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword control-flow" style="color:#00009f">return</span><span class="token plain"> compiler</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><button type="button" aria-label="Copy code to clipboard" title="Copy" class="copyButton_eDfN clean-btn"><span class="copyButtonIcons_W9eQ" aria-hidden="true"><svg class="copyButtonIcon_XEyF" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_i9w9" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="2-webpack-构建阶段做了什么">2. webpack 构建阶段做了什么<a class="hash-link" href="#2-webpack-构建阶段做了什么" title="Direct link to heading"></a></h3><p>在 webpack 函数执行完之后，就到主要的构建阶段，首先执行 compiler.run()，然后触发一系列钩子函数，执行 compiler.compile()。
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<img loading="lazy" src="https://user-images.githubusercontent.com/15681693/134162956-d7210d3a-2881-4d0c-b84b-0a1b813a8d0f.png" alt="webpack 执行流程" class="img_E7b_"></p><ol><li>在实例化 compiler 之后，执行 compiler.run()。</li><li>执行 newCompilation 函数，调用 createCompilation 初始化 Compilation 对象。</li><li>执行 <!-- -->_<!-- -->addEntryItem 将入口文件存入 this.entries（map 对象），遍历 this.entries 对象构建 chunk。</li><li>执行 handleModuleCreation，开始创建模块实例。</li><li>执行 moduleFactory.create 创建模块。<ol><li>执行 factory.hooks.factorize.call 钩子，然后会调用 ExternalModuleFactoryPlugin 中注册的钩子，用于配置外部文件的模块加载方式。</li><li>使用 enhanced-resolve 解析模块和 loader 的真实绝对路径。</li><li>执行 new NormalModule()创建 module 实例。</li></ol></li><li>执行 addModule，存储 module。</li><li>执行 buildModule，添加模块到模块队列 buildQueue，开始构建模块, 这里会调用 normalModule 中的 build 开启构建。<ol><li>创建 loader 上下文。</li><li>执行 runLoaders，通过 enhanced-resolve 解析得到的模块和 loader 的路径获取函数，执行 loader。</li><li>生成模块的 hash。</li></ol></li><li>所有依赖都解析完毕后，构建阶段结束。</li></ol><div class="codeBlockContainer_I0IT language-javascript theme-code-block"><div class="codeBlockContent_wNvx" style="color:#393A34;background-color:#f6f8fa"><pre tabindex="0" class="prism-code language-javascript codeBlock_jd64 thin-scrollbar"><code class="codeBlockLines_mRuA"><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 构建过程涉及流程比较复杂，代码会做省略</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// lib/webpack.js 1284行</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 开启编译流程</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> compiler</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">run</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">err</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> stats</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> compiler</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">close</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">err2</span><span class="token plain"> </span><span class="token arrow operator" style="color:#393A34">=></span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">callback</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">err </span><span class="token operator" style="color:#393A34">||</span><span class="token plain"> err2</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> stats</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// lib/compiler.js 1081行</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 开启编译流程</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">compile</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">callback</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> params </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">newCompilationParams</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 创建 Compilation 对象</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> </span><span class="token maybe-class-name">Compilation</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">newCompilation</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">params</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// lib/Compilation.js 1865行</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 确认入口文件</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">addEntry</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">_addEntryItem</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// lib/Compilation.js 1834行</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 开始创建模块流程，创建模块实例</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">addModuleTree</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">handleModuleCreation</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// lib/Compilation.js 1548行</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 开始创建模块流程，创建模块实例</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">handleModuleCreation</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">factorizeModule</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// lib/Compilation.js 1712行</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 添加到创建模块队列，执行创建模块</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">factorizeModule</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">options</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> callback</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">factorizeQueue</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">add</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">options</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> callback</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// lib/Compilation.js 1834行</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 保存需要构建模块</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">_addModule</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">module</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> callback</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">modules</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">add</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">module</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// lib/Compilation.js 1284行</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 添加模块进模块编译队列，开始编译</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">buildModule</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">module</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> callback</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">buildQueue</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">add</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">module</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> callback</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><br></span></code></pre><button type="button" aria-label="Copy code to clipboard" title="Copy" class="copyButton_eDfN clean-btn"><span class="copyButtonIcons_W9eQ" aria-hidden="true"><svg class="copyButtonIcon_XEyF" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_i9w9" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="3-webpack-生成阶段做了什么">3. webpack 生成阶段做了什么<a class="hash-link" href="#3-webpack-生成阶段做了什么" title="Direct link to heading"></a></h3><p>构建阶段围绕 module 展开，生成阶段则围绕 chunks 展开。经过构建阶段之后，webpack 得到足够的模块内容与模块关系信息，之后通过 Compilation.seal 函数生成最终资源。</p><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="31-生成产物">3.1 生成产物<a class="hash-link" href="#31-生成产物" title="Direct link to heading"></a></h4><p>执行 Compilation.seal 进行产物的封装。</p><ol><li>构建本次编译的 ChunkGraph 对象，执行 buildChunkGraph，这里会将 import()、require.ensure 等方法生成的动态模块添加到 chunks 中。</li><li>遍历 Compilation.modules 集合，将 module 按 <strong>entry/动态引入</strong> 的规则分配给不同的 Chunk 对象。</li><li>调用 Compilation.emitAssets 方法将 assets 信息记录到 Compilation.assets 对象中。</li><li>执行 hooks.optimizeChunkModules 的钩子，这里开始进行代码生成和封装。<ol><li>执行一系列钩子函数（reviveModules, moduleId, optimizeChunkIds 等）。</li><li>执行 createModuleHashes 更新模块 hash。</li><li>执行 JavascriptGenerator 生成模块代码，这里会遍历 modules，创建构建任务，循环使用 JavascriptGenerator 构建代码，这时会将 import 等模块引入方式替换为 <strong>webpack_require</strong> 等，并将生成结果存入缓存。</li><li>执行 processRuntimeRequirements，根据生成的内容所使用到的 webpack_require 的函数，添加对应的代码。</li><li>执行 createHash 创建 chunk 的 hash。</li><li>执行 clearAssets 清除 chunk 的 files 和 auxiliary，这里缓存的是生成的 chunk 的文件名，主要是清除上次构建产生的废弃内容。</li></ol></li></ol><h4 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="32-文件输出">3.2 文件输出<a class="hash-link" href="#32-文件输出" title="Direct link to heading"></a></h4><p>回到 Compiler 的流程中，执行 onCompiled 回调。</p><ol><li>触发 shouldEmit 钩子函数，这里是最后能优化产物的钩子。</li><li>遍历 module 集合，根据 entry 配置及引入资源的方式，将 module 分配到不同的 chunk。</li><li>遍历 chunk 集合，调用 Compilation.emitAsset 方法标记 chunk 的输出规则，即转化为 assets 集合。</li><li>写入本地文件，用的是 webpack 函数执行时初始化的文件流工具。</li><li>执行 done 钩子函数，这里会执行 compiler.run() 的回调，再执行 compiler.close()，然后执行持久化存储（前提是使用的 filesystem 缓存模式）。</li></ol><h2 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="参考资料">参考资料<a class="hash-link" href="#参考资料" title="Direct link to heading"></a></h2><ol><li><a href="https://webpack.js.org/" target="_blank" rel="noopener noreferrer">webpack5 官方文档</a></li><li><a href="https://www.npmjs.com/package/acorn" target="_blank" rel="noopener noreferrer">acorn</a></li></ol></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><div class="pagination-nav__item"><a class="pagination-nav__link" href="/awesome-interview/book1/browser-repain-reflow"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">浏览器：浏览器的重排重绘</div></a></div><div class="pagination-nav__item pagination-nav__item--next"><a class="pagination-nav__link" href="/awesome-interview/book1/frame-vue-data-binding"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">框架：Vue 的数据绑定机制</div></a></div></nav></div></div><div class="col col--3"><div class="tableOfContents_cNA8 thin-scrollbar theme-doc-toc-desktop"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#相关问题" class="table-of-contents__link toc-highlight">相关问题</a></li><li><a href="#回答关键点" class="table-of-contents__link toc-highlight">回答关键点</a></li><li><a href="#知识点深入" class="table-of-contents__link toc-highlight">知识点深入</a><ul><li><a href="#1-webpack-初始化过程" class="table-of-contents__link toc-highlight">1. webpack 初始化过程</a></li><li><a href="#2-webpack-构建阶段做了什么" class="table-of-contents__link toc-highlight">2. webpack 构建阶段做了什么</a></li><li><a href="#3-webpack-生成阶段做了什么" class="table-of-contents__link toc-highlight">3. webpack 生成阶段做了什么</a><ul><li><a href="#31-生成产物" class="table-of-contents__link toc-highlight">3.1 生成产物</a></li><li><a href="#32-文件输出" class="table-of-contents__link toc-highlight">3.2 文件输出</a></li></ul></li></ul></li><li><a href="#参考资料" class="table-of-contents__link toc-highlight">参考资料</a></li></ul></div></div></div><div class="row"><div class="col"><div class="react-utterences"><div>Loading script...</div></div></div><div class="col col--3"></div></div></div></main></div></div></div>
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