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padding-bottom--lg"><div class="row"><div class="col docItemCol_DM6M"><div 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">模拟题二</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">框架：React Fiber 的作用和原理</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>React Fiber 的作用和原理</h1><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>Fiber 是什么</li><li>谈谈你对 Fiber 的了解</li><li>Fiber 对 React 的使用带来了什么影响</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>调度</code> <code>深度优先遍历</code></p><p>Fiber 是 React 16 中采用的新协调（reconciliation）引擎，主要目标是支持虚拟 DOM 的渐进式渲染。</p><p>Fiber 将原有的 Stack Reconciler 替换为 Fiber Reconciler，提高了复杂应用的可响应性和性能。主要通过以下方式达成目标：</p><ul><li>对大型复杂任务的分片。</li><li>对任务划分优先级，优先调度高优先级的任务。</li><li>调度过程中，可以对任务进行挂起、恢复、终止等操作。</li></ul><p>Fiber 对现有代码的影响：
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由于 Fiber 采用了全新的调度方式，任务的更新过程可能会被打断，这意味着在组件更新过程中，render 及其之前的生命周期函数可能会调用多次。因此，在下列生命周期函数中不应出现副作用。</p><ul><li>shouldComponentUpdate</li><li>React 16 中已经声明废弃的钩子<ul><li>componentWillMount（UNSAFE_componentWillMount）</li><li>componentWillReceiveProps（UNSAFE_componentWillReceiveProps）</li><li>componentWillUpdate（UNSAFE_componentWillUpdate）</li></ul></li></ul><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-react-是如何工作的">1. React 是如何工作的<a class="hash-link" href="#1-react-是如何工作的" title="Direct link to heading"></a></h3><div class="codeBlockContainer_I0IT language-jsx theme-code-block"><div class="codeBlockContent_wNvx" style="color:#393A34;background-color:#f6f8fa"><pre tabindex="0" class="prism-code language-jsx codeBlock_jd64 thin-scrollbar"><code class="codeBlockLines_mRuA"><span class="token-line" style="color:#393A34"><span class="token keyword" style="color:#00009f">import</span><span class="token plain"> React </span><span class="token keyword" style="color:#00009f">from</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"react"</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">import</span><span class="token plain"> ReactDOM </span><span class="token keyword" style="color:#00009f">from</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"react-dom"</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 keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">App</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">return</span><span class="token plain"> </span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag" style="color:#00009f">div</span><span class="token tag punctuation" style="color:#393A34">></span><span class="token plain-text">Hello, HZFE.</span><span class="token tag punctuation" style="color:#393A34"></</span><span class="token tag" style="color:#00009f">div</span><span class="token tag 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">ReactDOM</span><span class="token punctuation" style="color:#393A34">.</span><span class="token function" style="color:#d73a49">render</span><span class="token punctuation" style="color:#393A34">(</span><span class="token tag punctuation" style="color:#393A34"><</span><span class="token tag class-name" style="color:#00009f">App</span><span class="token tag" style="color:#00009f"> </span><span class="token tag punctuation" style="color:#393A34">/></span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> document</span><span class="token punctuation" style="color:#393A34">.</span><span class="token function" style="color:#d73a49">getElementById</span><span class="token punctuation" style="color:#393A34">(</span><span class="token string" style="color:#e3116c">"root"</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><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><p>上面代码中我们引入的两个包，分别代表了 React 的 core API 层和渲染层，在这背后还有一层被称为协调器（Reconcilers）的层次。（协调器在<a href="https://github.com/facebook/react/tree/main/packages/react-reconciler" target="_blank" rel="noopener noreferrer">react-reconciler</a>中实现）</p><p>一个 React 组件的渲染主要经历两个阶段：</p><ul><li>调度阶段（Reconciler）：用新的数据生成一棵新的树，然后通过 Diff 算法，遍历旧的树，快速找出需要更新的元素，放到更新队列中去，得到新的更新队列。</li><li>渲染阶段（Renderer）：遍历更新队列，通过调用宿主环境的 API，实际更新渲染对应的元素。宿主环境如 DOM，Native 等。</li></ul><p>对于调度阶段，新老架构中有不同的处理方式：</p><p>React 16 之前使用的是 Stack Reconciler（栈协调器），使用递归的方式创建虚拟 DOM，递归的过程是不能中断的。如果组件树的层级很深，递归更新组件的时间超过 16ms（以 60Hz 频率的显示器为例，浏览器绘制一帧的最小时间间隔为 1/60s 约等于 16ms），这时会发生俗称的掉帧现象，帧率不稳定时，用户就会感觉到卡顿。</p><p><img loading="lazy" src="https://user-images.githubusercontent.com/4338052/127518991-bea34058-35fc-4712-94d7-a3fc8df21df4.png" alt="image" class="img_E7b_"></p><blockquote><p>图片来源 <a href="https://www.youtube.com/watch?v=5Wd5rxT7e1U&list=PLb0IAmt7-GS3fZ46IGFirdqKTIxlws7e0&index=4" target="_blank" rel="noopener noreferrer">react conf 17</a></p></blockquote><p>React 16 及以后使用的是 Fiber Reconciler（纤维协调器），将递归中无法中断的更新重构为迭代中的异步可中断更新过程，这样就能够更好的控制组件的渲染。</p><p><img loading="lazy" src="https://user-images.githubusercontent.com/4338052/127519057-56e3a47a-19b4-42b0-9ad6-02b543c633cc.png" alt="image" class="img_E7b_"></p><blockquote><p>图片来源 <a href="https://www.youtube.com/watch?v=5Wd5rxT7e1U&list=PLb0IAmt7-GS3fZ46IGFirdqKTIxlws7e0&index=4" target="_blank" rel="noopener noreferrer">react conf 17</a></p></blockquote><h3 class="anchor anchorWithHideOnScrollNavbar_R0VQ" id="2-fiber-reconciler-如何工作">2. Fiber Reconciler 如何工作<a class="hash-link" href="#2-fiber-reconciler-如何工作" title="Direct link to heading"></a></h3><p>由于浏览器中 JS 的运行环境是单线程的，因此，一旦有任务耗时过长，就会阻塞其他任务的执行，导致浏览器不能及时响应用户的操作，从而使用户体验下降。为解决这个问题，React 推出了 Fiber Reconciler 架构。</p><p>在 Fiber 中，会把一个耗时很长的任务分成很多小的任务片，每一个任务片的运行时间很短。虽然总的任务执行时间依然很长，但是在每个任务小片执行完之后，都会给其他任务一个执行机会。
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这样，唯一的线程就不会被独占，其他任务也能够得到执行机会。</p><p>为了实现渐进渲染的目的，Fiber 架构中引入了新的数据结构：Fiber Node，Fiber Node Tree 根据 React Element Tree 生成，并用来驱动真实 DOM 的渲染。</p><p>Fiber 节点的大致结构：</p><div class="codeBlockContainer_I0IT language-js theme-code-block"><div class="codeBlockContent_wNvx" style="color:#393A34;background-color:#f6f8fa"><pre tabindex="0" class="prism-code language-js codeBlock_jd64 thin-scrollbar"><code class="codeBlockLines_mRuA"><span class="token-line" style="color:#393A34"><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">tag</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">TypeOfWork</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 标识 fiber 类型</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">type</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">'div'</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 和 fiber 相关的组件类型</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 operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Fiber</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">|</span><span class="token plain"> </span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 父节点</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">child</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Fiber</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">|</span><span class="token plain"> </span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 子节点</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">sibling</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Fiber</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">|</span><span class="token plain"> </span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 同级节点</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">alternate</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Fiber</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">|</span><span class="token plain"> </span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// diff 的变化记录在这个节点上</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token spread operator" 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><p>Fiber 树结构如下：</p><p><img loading="lazy" src="https://user-images.githubusercontent.com/11912260/44942438-4c0e7f00-ade3-11e8-83ea-161e2aedcf8e.png" alt="Fiber Tree" class="img_E7b_"></p><blockquote><p>图片来源 <a href="https://www.youtube.com/watch?v=5Wd5rxT7e1U&list=PLb0IAmt7-GS3fZ46IGFirdqKTIxlws7e0&index=4" target="_blank" rel="noopener noreferrer">react conf 17</a></p></blockquote><p>Fiber 的主要工作流程：</p><ol><li><code>ReactDOM.render()</code> 引导 React 启动或调用 <code>setState()</code> 的时候开始创建或更新 Fiber 树。</li><li>从根节点开始遍历 Fiber Node Tree， 并且构建 workInProgress Tree（reconciliation 阶段）。<ul><li>本阶段可以暂停、终止、和重启，会导致 react 相关生命周期重复执行。</li><li>React 会生成两棵树，一棵是代表当前状态的 current tree，一棵是待更新的 workInProgress tree。</li><li>遍历 current tree，重用或更新 Fiber Node 到 workInProgress tree，workInProgress tree 完成后会替换 current tree。</li><li>每更新一个节点，同时生成该节点对应的 Effect List。</li><li>为每个节点创建更新任务。</li></ul></li><li>将创建的更新任务加入任务队列，等待调度。<ul><li>调度由 scheduler 模块完成，其核心职责是执行回调。</li><li>scheduler 模块实现了跨平台兼容的 requestIdleCallback。</li><li>每处理完一个 Fiber Node 的更新，可以中断、挂起，或恢复。</li></ul></li><li>根据 Effect List 更新 DOM （commit 阶段）。<ul><li>React 会遍历 Effect List 将所有变更一次性更新到 DOM 上。</li><li>这一阶段的工作会导致用户可见的变化。因此该过程不可中断，必须一直执行直到更新完成。</li></ul></li></ol><p>React 调度流程图：</p><p><img loading="lazy" src="https://user-images.githubusercontent.com/4338052/127530996-23513132-f3ef-4a3e-8553-8bfef2e3669b.png" alt="image" class="img_E7b_"></p><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://github.com/acdlite/react-fiber-architecture" target="_blank" rel="noopener noreferrer">React Fiber Architecture</a></li><li><a href="https://www.youtube.com/watch?v=7HSd1sk07uU&list=PLb0IAmt7-GS3fZ46IGFirdqKTIxlws7e0" target="_blank" rel="noopener noreferrer">React Conf 2017</a></li><li><a href="https://blog.ag-grid.com/inside-fiber-an-in-depth-overview-of-the-new-reconciliation-algorithm-in-react/" target="_blank" rel="noopener noreferrer">Inside Fiber</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/engineer-babel"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">工程化：Babel 的原理</div></a></div><div class="pagination-nav__item pagination-nav__item--next"><a class="pagination-nav__link" href="/awesome-interview/book2/frame-react-hoc-hooks"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">框架：HOC vs Render Props vs Hooks</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-react-是如何工作的" class="table-of-contents__link toc-highlight">1. 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