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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>React Hooks 实现原理</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>React Hooks 是什么</li><li>React Hooks 是怎么实现的</li><li>使用 React Hooks 需要注意什么</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>闭包</code> <code>Fiber</code> <code>链表</code></p><p>Hooks 是 React 16.8 的新增特性。它可以让你在不编写 class 的情况下使用 state 以及其他的 React 特性。</p><p>Hooks 主要是利用闭包来保存状态，使用链表保存一系列 Hooks，将链表中的第一个 Hook 与 Fiber 关联。在 Fiber 树更新时，就能从 Hooks 中计算出最终输出的状态和执行相关的副作用。</p><p>使用 Hooks 的注意事项：</p><ul><li>不要在循环，条件或嵌套函数中调用 Hooks。</li><li>只在 React 函数中调用 Hooks。</li></ul><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-简化实现"></a>1. 简化实现<a class="hash-link" href="#1-简化实现" title="Direct link to heading">#</a></h3><p><a href="https://codesandbox.io/s/hopeful-williams-id7ey?file=/src/index.js" target="_blank" rel="noopener noreferrer">React Hooks 模拟实现</a></p><p>该示例是一个 React Hooks 接口的简化模拟实现，可以实际运行观察。其中 <code>react.js</code> 文件模拟实现了 <code>useState</code> 和 <code>useEffect</code> 接口，其基本原理和 react 实际实现类似。</p><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="2-对比分析"></a>2. 对比分析<a class="hash-link" href="#2-对比分析" title="Direct link to heading">#</a></h3><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="21-状态-hook"></a>2.1 状态 Hook<a class="hash-link" href="#21-状态-hook" title="Direct link to heading">#</a></h4><p>模拟的 useState 实现中，通过闭包，将 state 保存在 <code>memoizedState[cursor]</code>。 memoizedState 是一个数组，可以按顺序保存 hook 多次调用产生的状态。</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">let</span><span class="token plain"> memoizedState </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 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" style="color:#00009f">let</span><span class="token plain"> cursor </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">0</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" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">useState</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">initialValue</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 comment" style="color:#999988;font-style:italic">// 初次调用时，传入的初始值作为 state，后续使用闭包中保存的 state</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">let</span><span class="token plain"> state </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> memoizedState</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">cursor</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">??</span><span class="token plain"> initialValue</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">// 对游标进行闭包缓存，使得 setState 调用时，操作正确的对应状态</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">const</span><span class="token plain"> _cursor </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> cursor</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" style="color:#00009f">const</span><span class="token plain"> </span><span class="token function-variable function" style="color:#d73a49">setState</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">newValue</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">memoizedState</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">_cursor</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> newValue</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">// 游标自增，为接下来调用的 hook 使用时，引用 memoizedState 中的新位置</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> cursor </span><span class="token operator" style="color:#393A34">+=</span><span class="token plain"> </span><span class="token number" style="color:#36acaa">1</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">state</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> setState</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>实际的 useState 实现经过多方面的<a href="https://overreacted.io/why-do-hooks-rely-on-call-order/" target="_blank" rel="noopener noreferrer">综合考虑</a>，React 最终选择将 Hooks 设计为顺序结构，这也是 Hooks 不能条件调用的原因。</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">function</span><span class="token plain"> mountState</span><span class="token operator" style="color:#393A34"><</span><span class="token constant" style="color:#36acaa">S</span><span class="token operator" 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"> initialState</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 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 constant" style="color:#36acaa">S</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">|</span><span class="token plain"> </span><span class="token constant" style="color:#36acaa">S</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 operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token constant" style="color:#36acaa">S</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token maybe-class-name">Dispatch</span><span class="token operator" style="color:#393A34"><</span><span class="token maybe-class-name">BasicStateAction</span><span class="token operator" style="color:#393A34"><</span><span class="token constant" style="color:#36acaa">S</span><span class="token operator" 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 comment" style="color:#999988;font-style:italic">// 创建 Hook，并将当前 Hook 添加到 Hooks 链表中</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">const</span><span class="token plain"> hook </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">mountWorkInProgressHook</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">// 如果初始值是函数，则调用函数取得初始值</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">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"> initialState </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></span><span class="token-line" style="color:#393A34"><span class="token plain"> initialState </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">initialState</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 plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> hook</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">memoizedState</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> hook</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">baseState</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> initialState</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">// 创建一个链表来存放更新对象</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">const</span><span class="token plain"> queue </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">hook</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">queue</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 plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> pending</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><span class="token-line" style="color:#393A34"><span class="token plain"> dispatch</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><span class="token-line" style="color:#393A34"><span class="token plain"> lastRenderedReducer</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> basicStateReducer</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"> lastRenderedState</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> initialState</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 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">// dispatch 用于修改状态，并将此次更新添加到更新对象链表中</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">const</span><span class="token plain"> dispatch</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Dispatch</span><span class="token operator" style="color:#393A34"><</span><span class="token maybe-class-name">BasicStateAction</span><span class="token operator" style="color:#393A34"><</span><span class="token constant" style="color:#36acaa">S</span><span class="token operator" style="color:#393A34">>></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 plain">queue</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">dispatch</span><span class="token plain"> </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 punctuation" style="color:#393A34">(</span><span class="token plain">dispatchAction</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">bind</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword null nil" style="color:#00009f">null</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> currentlyRenderingFiber</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> queue</span><span class="token punctuation" style="color:#393A34">)</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> any</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 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">hook</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">memoizedState</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> dispatch</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><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="21-副作用-hook"></a>2.1 副作用 Hook<a class="hash-link" href="#21-副作用-hook" title="Direct link to heading">#</a></h4><p>模拟的 useEffect 实现，同样利用了 memoizedState 闭包来存储依赖数组。依赖数组进行浅比较，默认的比较算法是 <code>Object.is</code>。</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">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">useEffect</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">cb</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> depArray</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" style="color:#00009f">const</span><span class="token plain"> oldDeps </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> memoizedState</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">cursor</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 keyword" style="color:#00009f">let</span><span class="token plain"> hasChange </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token boolean" style="color:#36acaa">true</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">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">oldDeps</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 comment" style="color:#999988;font-style:italic">// 对比传入的依赖数组与闭包中保存的旧依赖数组，采用浅比较算法</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> hasChange </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> depArray</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">some</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">dep</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> i</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 operator" style="color:#393A34">!</span><span class="token known-class-name class-name">Object</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">is</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">dep</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> oldDeps</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">i</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 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"> </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 plain">hasChange</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">cb</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"> memoizedState</span><span class="token punctuation" style="color:#393A34">[</span><span class="token plain">cursor</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> depArray</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"> cursor</span><span class="token operator" 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>实际的 useEffect 实现：</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">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">mountEffect</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-variable function" style="color:#d73a49">create</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 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 keyword" style="color:#00009f">void</span><span class="token punctuation" style="color:#393A34">)</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"> deps</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Array</span><span class="token operator" style="color:#393A34"><</span><span class="token plain">mixed</span><span class="token operator" style="color:#393A34">></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 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 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 operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">void</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 function" style="color:#d73a49">mountEffectImpl</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 maybe-class-name">UpdateEffect</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">|</span><span class="token plain"> </span><span class="token maybe-class-name">PassiveEffect</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// fiberFlags</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token maybe-class-name">HookPassive</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// hookFlags</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> create</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"> deps</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"></span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">mountEffectImpl</span><span class="token punctuation" style="color:#393A34">(</span><span class="token parameter">fiberFlags</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> hookFlags</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> create</span><span class="token parameter punctuation" style="color:#393A34">,</span><span class="token parameter"> deps</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 keyword" style="color:#00009f">void</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">// 创建hook</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">const</span><span class="token plain"> hook </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">mountWorkInProgressHook</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 keyword" style="color:#00009f">const</span><span class="token plain"> nextDeps </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> deps </span><span class="token operator" style="color:#393A34">===</span><span class="token plain"> </span><span class="token keyword nil" 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 null nil" style="color:#00009f">null</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> deps</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">// 设置 workInProgress 的副作用标记</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> currentlyRenderingFiber</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">flags</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">|=</span><span class="token plain"> fiberFlags</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// fiberFlags 被标记到 workInProgress</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">// 创建 Effect, 挂载到 hook.memoizedState 上</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> hook</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">memoizedState</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">pushEffect</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 maybe-class-name">HookHasEffect</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">|</span><span class="token plain"> hookFlags</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// hookFlags 用于创建 effect</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> create</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 nil" style="color:#00009f">undefined</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"> nextDeps</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><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="3-hooks-如何与-fiber-共同工作"></a>3. Hooks 如何与 Fiber 共同工作<a class="hash-link" href="#3-hooks-如何与-fiber-共同工作" title="Direct link to heading">#</a></h3><p>在了解如何工作之前，先看看 Hook 与 Fiber 的部分结构定义：</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 module" style="color:#00009f">export</span><span class="token plain"> type </span><span class="token maybe-class-name">Hook</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 plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> memoizedState</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> any</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 最新的状态值</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> baseState</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> any</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 初始状态值</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> baseQueue</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Update</span><span class="token operator" style="color:#393A34"><</span><span class="token plain">any</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> any</span><span class="token operator" style="color:#393A34">></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><span class="token-line" style="color:#393A34"><span class="token plain"> queue</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">UpdateQueue</span><span class="token operator" style="color:#393A34"><</span><span class="token plain">any</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> any</span><span class="token operator" style="color:#393A34">></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">// 环形链表，存储的是该 hook 多次调用产生的更新对象</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> next</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Hook</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">// next 指针，之下链表中的下一个 Hook</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><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 module" style="color:#00009f">export</span><span class="token plain"> type </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 punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> updateQueue</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> mixed</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 存储 Fiber 节点相关的副作用链表</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> memoizedState</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> any</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 存储 Fiber 节点相关的状态值</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> flags</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Flags</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 标识当前 Fiber 节点是否有副作用</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>与上节中的模拟实现不同，真实的 Hooks 是一个单链表的结构，React 按 Hooks 的执行顺序依次将 Hook 节点添加到链表中。下面以 useState 和 useEffect 两个最常用的 hook 为例，来分析 Hooks 如何与 Fiber 共同工作。</p><p>在每个<strong>状态 Hook</strong>（如 useState）节点中，会通过 queue 属性上的循环链表记住所有的更新操作，并在 updade 阶段依次执行循环链表中的所有更新操作，最终拿到最新的 state 返回。</p><p>状态 Hooks 组成的链表的具体结构如下图所示：</p><p><img src="https://user-images.githubusercontent.com/4338052/130256374-80a453a4-2084-4bb8-bfba-2344f25100c4.png" alt="State Hook"></p><p>在每个<strong>副作用 Hook</strong>（如 useEffect）节点中，创建 effect 挂载到 Hook 的 memoizedState 中，并添加到环形链表的末尾，该链表会保存到 Fiber 节点的 updateQueue 中，在 commit 阶段执行。</p><p>副作用 Hooks 组成的链表的具体结构如下图所示：</p><p><img src="https://user-images.githubusercontent.com/4338052/130258719-4a2ad7d5-3a0b-4f9c-b278-1f35a0b96843.png" alt="Effect Hook"></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://overreacted.io/why-do-hooks-rely-on-call-order/" target="_blank" rel="noopener noreferrer">Why Do React Hooks Rely on Call Order?</a></li><li><a href="https://medium.com/@ryardley/react-hooks-not-magic-just-arrays-cd4f1857236e" target="_blank" rel="noopener noreferrer">React hooks: not magic, just arrays</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/book3/engineer-webpack-loader"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">« 工程化：谈下 webpack loader 的机制</div></a></div><div class="pagination-nav__item pagination-nav__item--next"><a class="pagination-nav__link" href="/awesome-interview/book3/frame-diff"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">框架：常见框架的 Diff 算法 »</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-简化实现" class="table-of-contents__link">1. 简化实现</a></li><li><a href="#2-对比分析" class="table-of-contents__link">2. 对比分析</a></li><li><a href="#3-hooks-如何与-fiber-共同工作" class="table-of-contents__link">3. Hooks 如何与 Fiber 共同工作</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>
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