22 lines
39 KiB
HTML
22 lines
39 KiB
HTML
<!doctype html>
|
||
<html lang="en" dir="ltr">
|
||
<head>
|
||
<meta charset="UTF-8">
|
||
<meta name="viewport" content="width=device-width,initial-scale=1">
|
||
<meta name="generator" content="Docusaurus v2.0.0-beta.5">
|
||
<link rel="search" type="application/opensearchdescription+xml" title="HZFE - 剑指前端 Offer" href="/awesome-interview/opensearch.xml">
|
||
<link rel="preconnect" href="https://hm.baidu.com">
|
||
<script>var _hmt=_hmt||[];!function(){var e=document.createElement("script");e.src="https://hm.baidu.com/hm.js?c7cd0fd77ac518cc6ef46461cdc9524b";var c=document.getElementsByTagName("script")[0];c.parentNode.insertBefore(e,c)}()</script><title data-react-helmet="true">Babel 的原理 | HZFE - 剑指前端 Offer</title><meta data-react-helmet="true" name="twitter:card" content="summary_large_image"><meta data-react-helmet="true" property="og:url" content="https://hzfe.github.io/awesome-interview/book2/engineer-babel"><meta data-react-helmet="true" name="docsearch:language" content="en"><meta data-react-helmet="true" name="docsearch:version" content="current"><meta data-react-helmet="true" name="docsearch:docusaurus_tag" content="docs-default-current"><meta data-react-helmet="true" property="og:title" content="Babel 的原理 | HZFE - 剑指前端 Offer"><meta data-react-helmet="true" name="description" content="相关问题"><meta data-react-helmet="true" property="og:description" content="相关问题"><link data-react-helmet="true" rel="shortcut icon" href="/awesome-interview/img/favicon.ico"><link data-react-helmet="true" rel="canonical" href="https://hzfe.github.io/awesome-interview/book2/engineer-babel"><link data-react-helmet="true" rel="alternate" href="https://hzfe.github.io/awesome-interview/book2/engineer-babel" hreflang="en"><link data-react-helmet="true" rel="alternate" href="https://hzfe.github.io/awesome-interview/book2/engineer-babel" hreflang="x-default"><link data-react-helmet="true" rel="preconnect" href="https://61YWQXP6JY-dsn.algolia.net" crossorigin="anonymous"><link rel="stylesheet" href="/awesome-interview/assets/css/styles.304d13b7.css">
|
||
<link rel="preload" href="/awesome-interview/assets/js/runtime~main.50b7dd91.js" as="script">
|
||
<link rel="preload" href="/awesome-interview/assets/js/main.178fbfc5.js" as="script">
|
||
</head>
|
||
<body>
|
||
<script>!function(){function t(t){document.documentElement.setAttribute("data-theme",t)}var e=function(){var t=null;try{t=localStorage.getItem("theme")}catch(t){}return t}();t(null!==e?e:"light")}()</script><div id="__docusaurus">
|
||
<div><a href="#" class="skipToContent_1oUP">Skip to main content</a></div><nav class="navbar navbar--fixed-top navbarHideable_2qcr"><div class="navbar__inner"><div class="navbar__items"><button aria-label="Navigation bar toggle" class="navbar__toggle clean-btn" type="button" tabindex="0"><svg width="30" height="30" viewBox="0 0 30 30" aria-hidden="true"><path stroke="currentColor" stroke-linecap="round" stroke-miterlimit="10" stroke-width="2" d="M4 7h22M4 15h22M4 23h22"></path></svg></button><a class="navbar__brand" href="/awesome-interview/"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_1VuW themedImage--light_3UqQ navbar__logo"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_1VuW themedImage--dark_hz6m navbar__logo"><b class="navbar__title">剑指前端 Offer</b></a></div><div class="navbar__items navbar__items--right"><a href="https://github.com/hzfe/awesome-interview" target="_blank" rel="noopener noreferrer" class="navbar__item navbar__link"><span>GitHub<svg width="13.5" height="13.5" aria-hidden="true" viewBox="0 0 24 24" class="iconExternalLink_3J9K"><path fill="currentColor" d="M21 13v10h-21v-19h12v2h-10v15h17v-8h2zm3-12h-10.988l4.035 4-6.977 7.07 2.828 2.828 6.977-7.07 4.125 4.172v-11z"></path></svg></span></a><div class="searchBox_1Doo"><button type="button" class="DocSearch DocSearch-Button" aria-label="Search"><span class="DocSearch-Button-Container"><svg width="20" height="20" class="DocSearch-Search-Icon" viewBox="0 0 20 20"><path d="M14.386 14.386l4.0877 4.0877-4.0877-4.0877c-2.9418 2.9419-7.7115 2.9419-10.6533 0-2.9419-2.9418-2.9419-7.7115 0-10.6533 2.9418-2.9419 7.7115-2.9419 10.6533 0 2.9419 2.9418 2.9419 7.7115 0 10.6533z" stroke="currentColor" fill="none" fill-rule="evenodd" stroke-linecap="round" stroke-linejoin="round"></path></svg><span class="DocSearch-Button-Placeholder">Search</span></span><span class="DocSearch-Button-Keys"></span></button></div></div></div><div role="presentation" class="navbar-sidebar__backdrop"></div></nav><div class="main-wrapper docs-wrapper docs-doc-page"><div class="docPage_31aa"><button class="clean-btn backToTopButton_35hR" type="button"><svg viewBox="0 0 24 24" width="28"><path d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z" fill="currentColor"></path></svg></button><aside class="docSidebarContainer_3Kbt"><div class="sidebar_15mo sidebarWithHideableNavbar_267A"><a tabindex="-1" class="sidebarLogo_3h0W" href="/awesome-interview/"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_1VuW themedImage--light_3UqQ"><img src="/awesome-interview/img/badge.svg" alt="HZFE" class="themedImage_1VuW themedImage--dark_hz6m"><b>剑指前端 Offer</b></a><nav class="menu thin-scrollbar menu_Bmed menuWithAnnouncementBar_2WvA"><ul class="menu__list"><li class="menu__list-item"><a class="menu__link" href="/awesome-interview/about">关于我们</a></li><li class="menu__list-item"><a class="menu__link" href="/awesome-interview/">前言</a></li><li class="menu__list-item menu__list-item--collapsed"><a class="menu__link menu__link--sublist" href="#">模拟题一</a></li><li class="menu__list-item"><a class="menu__link menu__link--sublist menu__link--active" href="#">模拟题二</a><ul style="display:block;overflow:visible;height:auto" class="menu__list"><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/browser-render-mechanism">浏览器:浏览器渲染机制</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/browser-garbage">浏览器:垃圾回收机制</a></li><li class="menu__list-item"><a class="menu__link menu__link--active" aria-current="page" tabindex="0" href="/awesome-interview/book2/engineer-babel">工程化:Babel 的原理</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/frame-react-fiber">框架:React Fiber 的作用和原理</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/frame-react-hoc-hooks">框架:HOC vs Render Props vs Hooks</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/js-inherite">基础:ES5、ES6 如何实现继承</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/js-new">基础:New 操作符的原理</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/css-preprocessor">样式:谈谈 CSS 预处理器</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/network-http-cache">网络:HTTP 缓存机制</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/coding-throttle-debounce">编码:实现节流去抖函数</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/algorithm-reverse-linked-list">算法:反转链表</a></li><li class="menu__list-item"><a class="menu__link" tabindex="0" href="/awesome-interview/book2/topic-multi-pics-site-optimize">综合:多图站点性能优化</a></li></ul></li><li class="menu__list-item menu__list-item--collapsed"><a class="menu__link menu__link--sublist" href="#">模拟题三</a></li></ul></nav><button type="button" title="Collapse sidebar" aria-label="Collapse sidebar" class="button button--secondary button--outline collapseSidebarButton_1CGd"><svg width="20" height="20" aria-hidden="true" class="collapseSidebarButtonIcon_3E-R"><g fill="#7a7a7a"><path d="M9.992 10.023c0 .2-.062.399-.172.547l-4.996 7.492a.982.982 0 01-.828.454H1c-.55 0-1-.453-1-1 0-.2.059-.403.168-.551l4.629-6.942L.168 3.078A.939.939 0 010 2.528c0-.548.45-.997 1-.997h2.996c.352 0 .649.18.828.45L9.82 9.472c.11.148.172.347.172.55zm0 0"></path><path d="M19.98 10.023c0 .2-.058.399-.168.547l-4.996 7.492a.987.987 0 01-.828.454h-3c-.547 0-.996-.453-.996-1 0-.2.059-.403.168-.551l4.625-6.942-4.625-6.945a.939.939 0 01-.168-.55 1 1 0 01.996-.997h3c.348 0 .649.18.828.45l4.996 7.492c.11.148.168.347.168.55zm0 0"></path></g></svg></button></div></aside><main class="docMainContainer_3ufF"><div class="container padding-top--md padding-bottom--lg"><div class="row"><div class="col docItemCol_3FnS"><div class="docItemContainer_33ec"><article><div class="tocCollapsible_1PrD tocMobile_3Hoh"><button type="button" class="clean-btn tocCollapsibleButton_2O1e">On this page</button></div><div class="markdown"><header><h1>Babel 的原理</h1></header><h2><a aria-hidden="true" tabindex="-1" class="anchor anchor__h2 anchorWithHideOnScrollNavbar_3R7-" id="相关问题"></a>相关问题<a class="hash-link" href="#相关问题" title="Direct link to heading">#</a></h2><ul><li>Babel 是什么</li><li>Babel 有什么用</li><li>压缩代码如何实现</li></ul><h2><a aria-hidden="true" tabindex="-1" class="anchor anchor__h2 anchorWithHideOnScrollNavbar_3R7-" id="回答关键点"></a>回答关键点<a class="hash-link" href="#回答关键点" title="Direct link to heading">#</a></h2><p><code>JS 编译器</code> <code>AST</code> <code>插件系统</code></p><p>Babel 是 <strong>JavaScript 编译器</strong>:他能让开发者在开发过程中,直接使用各类方言(如 TS、Flow、JSX)或新的语法特性,而不需要考虑运行环境,因为 Babel 可以做到按需转换为低版本支持的代码;Babel 内部原理是将 JS 代码转换为 <strong>AST</strong>,对 AST 应用各种插件进行处理,最终输出编译后的 JS 代码。</p><h2><a aria-hidden="true" tabindex="-1" class="anchor anchor__h2 anchorWithHideOnScrollNavbar_3R7-" id="知识点深入"></a>知识点深入<a class="hash-link" href="#知识点深入" title="Direct link to heading">#</a></h2><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="1-ast-抽象语法树"></a>1. AST 抽象语法树<a class="hash-link" href="#1-ast-抽象语法树" title="Direct link to heading">#</a></h3><p><strong>简单定义</strong>:以树的形式来表现编程语言的语法结构。</p><p><img src="https://user-images.githubusercontent.com/17002181/124874255-1742bd80-dffa-11eb-9fcf-2a2f9e130334.png" alt="image"></p><p>利用在线 <a href="https://astexplorer.net/" target="_blank" rel="noopener noreferrer">playground</a> 调试,可以对 AST 有个直观感受:生成的树有多个节点,节点有不同的类型,不同类型节点有不同的属性。</p><div class="codeBlockContainer_K1bP"><div class="codeBlockContent_hGly js"><pre tabindex="0" class="prism-code language-js codeBlock_23N8 thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_39YC"><span class="token-line" style="color:#393A34"><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> custom </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"HZFE"</span><span class="token punctuation" style="color:#393A34">;</span></span></code></pre><button type="button" aria-label="Copy code to clipboard" class="copyButton_Ue-o clean-btn">Copy</button></div></div><p><img src="https://user-images.githubusercontent.com/17002181/124893664-7fe76580-e00d-11eb-8937-a6b7719643f4.png" alt="image"></p><p>AST 是源代码的高效表示,能便捷的表示大多数编程语言的结构。适用于做代码分析或转换等需求。之所以用树来进行分析或转换,是因为树能使得程序中的每一节点恰好被访问一次(前序或后续遍历)。</p><p><strong>常见使用场景</strong>:代码压缩混淆功能可以借助 AST 来实现:分析 AST,基于各种规则进行优化(如 IF 语句优化;移除不可访问代码;移除 debugger 等),从而生成更小的 AST 树,最终输出精简的代码结果。</p><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="2-babel-编译流程"></a>2. Babel 编译流程<a class="hash-link" href="#2-babel-编译流程" title="Direct link to heading">#</a></h3><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="三大步骤"></a>三大步骤<a class="hash-link" href="#三大步骤" title="Direct link to heading">#</a></h4><p><img src="https://user-images.githubusercontent.com/17002181/124876479-9f29c700-dffc-11eb-9eef-a4bc85ebb6be.png" alt="image"></p><ol><li><p><strong>解析阶段</strong>:Babel 默认使用 <strong>@babel/parser</strong> 将代码转换为 AST。解析一般分为两个阶段:词法分析和语法分析。</p><ul><li><strong>词法分析</strong>:对输入的字符序列做标记化(tokenization)操作。</li><li><strong>语法分析</strong>:处理标记与标记之间的关系,最终形成一颗完整的 AST 结构。</li></ul></li><li><p><strong>转换阶段</strong>:Babel 使用 <strong>@babel/traverse</strong> 提供的方法对 AST 进行深度优先遍历,调用插件对关注节点的处理函数,按需对 AST 节点进行增删改操作。</p></li><li><p><strong>生成阶段</strong>:Babel 默认使用 <strong>@babel/generator</strong> 将上一阶段处理后的 AST 转换为代码字符串。</p></li></ol><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="3-babel-插件系统"></a>3. Babel 插件系统<a class="hash-link" href="#3-babel-插件系统" title="Direct link to heading">#</a></h3><p>Babel 的核心模块 @babel/core,@babel/parser,@babel/traverse 和 @babel/generator 提供了完整的编译流程。而具体的转换逻辑需要插件来完成。</p><p>在使用 Babel 时,我们可通过配置文件指定 plugin 和 preset。而 preset 可以是 plugin 和 preset 以及其他配置的集合。Babel 会递归读取 preset,最终获取一个大的 plugins 数组,用于后续使用。</p><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="常见-presets"></a>常见 presets<a class="hash-link" href="#常见-presets" title="Direct link to heading">#</a></h4><ul><li>@babel/preset-env</li><li>@babel/preset-typescript</li><li>@babel/preset-react</li><li>@babel/preset-flow</li></ul><p>最常见的 @babel/preset-env 预设,包含了<a href="https://github.com/babel/babel/blob/master/packages/babel-compat-data/data/plugins.json" target="_blank" rel="noopener noreferrer">一组</a>最新浏览器已支持的 ES 语法特性,并且可以通过配置目标运行环境范围,自动按需引入插件。</p><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="编写-babel-插件"></a>编写 Babel 插件<a class="hash-link" href="#编写-babel-插件" title="Direct link to heading">#</a></h4><p>Babel 插件的写法是借助<strong>访问者模式</strong>(Visitor Pattern)对关注的节点定义处理函数。参考一个简单 Babel 插件例子:</p><div class="codeBlockContainer_K1bP"><div class="codeBlockContent_hGly js"><pre tabindex="0" class="prism-code language-js codeBlock_23N8 thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_39YC"><span class="token-line" style="color:#393A34"><span class="token plain">module</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method-variable function-variable method function property-access" style="color:#d73a49">exports</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">function</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 punctuation" style="color:#393A34">{</span><span class="token plain"></span></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"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">pre</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 punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 在 visitor 下挂载各种感兴趣的节点类型的监听方法</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> visitor</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 plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 对 Identify 类型的节点进行处理</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * @param {NodePath} path</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> */</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function maybe-class-name" style="color:#d73a49">Identifier</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">path</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></span><span class="token-line" style="color:#393A34"><span class="token plain"> path</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">node</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">name</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> path</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">node</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">name</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">toUpperCase</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></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></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></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">post</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 punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span></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></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></code></pre><button type="button" aria-label="Copy code to clipboard" class="copyButton_Ue-o clean-btn">Copy</button></div></div><p>使用该 Babel 插件的效果如下:</p><div class="codeBlockContainer_K1bP"><div class="codeBlockContent_hGly js"><pre tabindex="0" class="prism-code language-js codeBlock_23N8 thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_39YC"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">// input</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
|
||
</span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">// index.js</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">hzfe</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 punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
|
||
</span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">// .babelrc</span><span class="token plain"></span></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><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token string" style="color:#e3116c">"plugins"</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 string" style="color:#e3116c">"babel-plugin-yourpluginname"</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span></span></code></pre><button type="button" aria-label="Copy code to clipboard" class="copyButton_Ue-o clean-btn">Copy</button></div></div><div class="codeBlockContainer_K1bP"><div class="codeBlockContent_hGly js"><pre tabindex="0" class="prism-code language-js codeBlock_23N8 thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_39YC"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">// output</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token constant" style="color:#36acaa">HZFE</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 punctuation" style="color:#393A34">}</span></span></code></pre><button type="button" aria-label="Copy code to clipboard" class="copyButton_Ue-o clean-btn">Copy</button></div></div><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="深入-babel-转换阶段"></a>深入 Babel 转换阶段<a class="hash-link" href="#深入-babel-转换阶段" title="Direct link to heading">#</a></h4><p>在转换阶段,Babel 的相关方法会获得一个插件数组变量,用于后续的操作。插件结构可参考以下接口。</p><div class="codeBlockContainer_K1bP"><div class="codeBlockContent_hGly ts"><pre tabindex="0" class="prism-code language-ts codeBlock_23N8 thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_39YC"><span class="token-line" style="color:#393A34"><span class="token keyword" style="color:#00009f">interface</span><span class="token plain"> </span><span class="token class-name maybe-class-name">Plugin</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> key</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token builtin">string</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">undefined</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">null</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> post</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</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">void</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> pre</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</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">void</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> visitor</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Object</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> parserOverride</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</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">void</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> generatorOverride</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</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">void</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// ...</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span></span></code></pre><button type="button" aria-label="Copy code to clipboard" class="copyButton_Ue-o clean-btn">Copy</button></div></div><p><strong>转换阶段</strong>,Babel 会按以下顺序执行。详细逻辑可查看<a href="https://github.com/babel/babel/blob/a647b9ea6bdd510f0d80b58dbea66828016ffe00/packages/babel-core/src/transformation/index.ts#L76" target="_blank" rel="noopener noreferrer">源码</a>:</p><ol><li>执行所有插件的 pre 方法。</li><li>按需执行 visitor 中的方法。</li><li>执行所有插件的 post 方法。</li></ol><p>一般来说,写 Babel 插件主要使用到的是 visitor 对象,这个 visitor 对象中会书写对于关注的 AST 节点的处理逻辑。而上面执行顺序中的第二步所指的 visitor 对象,是整合自各插件的 visitor,最终形成一个大的 visitor 对象,大致的数据结构可参考以下接口:</p><div class="codeBlockContainer_K1bP"><div class="codeBlockContent_hGly ts"><pre tabindex="0" class="prism-code language-ts codeBlock_23N8 thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_39YC"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">// 书写插件时的 visitor 结构</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">interface</span><span class="token plain"> </span><span class="token class-name maybe-class-name">VisitorInPlugin</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token maybe-class-name">ASTNodeTypeName</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token builtin">string</span><span class="token punctuation" style="color:#393A34">]</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token operator" style="color:#393A34">|</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><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 plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> enter</span><span class="token operator" style="color:#393A34">?</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> exit</span><span class="token operator" style="color:#393A34">?</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></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></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><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
|
||
</span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token comment" style="color:#999988;font-style:italic">// babel 最终整合的 visitor 结构</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">interface</span><span class="token plain"> </span><span class="token class-name maybe-class-name">VisitorInTransform</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token maybe-class-name">ASTNodeTypeName</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token builtin">string</span><span class="token punctuation" style="color:#393A34">]</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 plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 不同插件对相同节点的处理会合并为数组</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> enter</span><span class="token operator" style="color:#393A34">?</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</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></span><span class="token-line" style="color:#393A34"><span class="token plain"> exit</span><span class="token operator" style="color:#393A34">?</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</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></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></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span></span></code></pre><button type="button" aria-label="Copy code to clipboard" class="copyButton_Ue-o clean-btn">Copy</button></div></div><p>在对 AST 进行<strong>深度优先遍历</strong>的过程中,会创建 TraversalContext 对象来把控对 NodePath 节点的访问,访问时调用对节点所定义的处理方法,从而实现按需执行 visitor 中的方法。详细实现请看 <a href="https://github.com/babel/babel/tree/bc1b9537b00499f462aa3ac0d49e30314a66f413/packages/babel-traverse" target="_blank" rel="noopener noreferrer">babel-traverse</a> 中的源码。</p><h2><a aria-hidden="true" tabindex="-1" class="anchor anchor__h2 anchorWithHideOnScrollNavbar_3R7-" id="参考资料"></a>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://en.wikipedia.org/wiki/Abstract_syntax_tree" target="_blank" rel="noopener noreferrer">AST</a></li><li><a href="https://github.com/jamiebuilds/babel-handbook" target="_blank" rel="noopener noreferrer">Babel-handbook</a></li><li><a href="https://github.com/estree/estree" target="_blank" rel="noopener noreferrer">estree</a></li><li><a href="https://en.wikipedia.org/wiki/Visitor_pattern" target="_blank" rel="noopener noreferrer">访问者模式</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/book2/browser-garbage"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">« 浏览器:垃圾回收机制</div></a></div><div class="pagination-nav__item pagination-nav__item--next"><a class="pagination-nav__link" href="/awesome-interview/book2/frame-react-fiber"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">框架:React Fiber 的作用和原理 »</div></a></div></nav></div></div><div class="col col--3"><div class="tableOfContents_35-E thin-scrollbar"><ul class="table-of-contents table-of-contents__left-border"><li><a href="#相关问题" class="table-of-contents__link">相关问题</a></li><li><a href="#回答关键点" class="table-of-contents__link">回答关键点</a></li><li><a href="#知识点深入" class="table-of-contents__link">知识点深入</a><ul><li><a href="#1-ast-抽象语法树" class="table-of-contents__link">1. AST 抽象语法树</a></li><li><a href="#2-babel-编译流程" class="table-of-contents__link">2. Babel 编译流程</a></li><li><a href="#3-babel-插件系统" class="table-of-contents__link">3. Babel 插件系统</a></li></ul></li><li><a href="#参考资料" class="table-of-contents__link">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>
|
||
<script src="/awesome-interview/assets/js/runtime~main.50b7dd91.js"></script>
|
||
<script src="/awesome-interview/assets/js/main.178fbfc5.js"></script>
|
||
</body>
|
||
</html> |