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class="clean-btn tocCollapsibleButton_TO0P">On this page</button></div><div class="theme-doc-markdown markdown"><h1>React 事件机制原理</h1><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="相关问题">相关问题<a href="#相关问题" class="hash-link" aria-label="Direct link to 相关问题" title="Direct link to 相关问题"></a></h2><ul><li>React 合成事件与原生 DOM 事件的区别</li><li>React 如何注册和触发事件</li><li>React 事件如何解决浏览器兼容问题</li></ul><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="回答关键点">回答关键点<a href="#回答关键点" class="hash-link" aria-label="Direct link to 回答关键点" title="Direct link to 回答关键点"></a></h2><p>React 的事件处理机制可以分为两个阶段:初始化渲染时在 root 节点上注册原生事件;原生事件触发时模拟捕获、目标和冒泡阶段派发合成事件。通过这种机制,冒泡的原生事件类型最多在 root 节点上注册一次,节省内存开销。且 React 为不同类型的事件定义了不同的处理优先级,从而让用户代码及时响应高优先级的用户交互,提升用户体验。</p><p>React 的事件机制中依赖合成事件这个核心概念。合成事件在符合 W3C 规范定义的前提下,抹平浏览器之间的差异化表现。并且简化事件逻辑,对关联事件进行合成。如每当表单类型组件的值发生改变时,都会触发 onChange 事件,而 onChange 事件由 change、click、input、keydown、keyup 等原生事件组成。</p><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="知识点深入">知识点深入<a href="#知识点深入" class="hash-link" aria-label="Direct link to 知识点深入" title="Direct link to 知识点深入"></a></h2><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="1-原生事件和合成事件">1. 原生事件和合成事件<a href="#1-原生事件和合成事件" class="hash-link" aria-label="Direct link to 1. 原生事件和合成事件" title="Direct link to 1. 原生事件和合成事件"></a></h3><p>JavaScript 通过事件可以和 DOM 进行交互。</p><h4 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="11-原生事件">1.1 原生事件<a href="#11-原生事件" class="hash-link" aria-label="Direct link to 1.1 原生事件" title="Direct link to 1.1 原生事件"></a></h4><p>主流浏览器基于 DOM2、DOM3 规范,实现标准化 DOM 事件。基于 Event 实现了浏览器中常见的用户事件如 UIEvent、InputEvent、MouseEvent 等。</p><p>在事件发生时,相关信息会存储在 Event 的实例对象中,对象包含 currentTarget、detail、target、preventDefault()、stopPropagation() 等属性和方法。DOM 节点可以通过 addEventListener 和 removeEventListener 来添加或移除事件监听函数。</p><div class="language-ts codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-ts codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">// Event 属性</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> bubbles</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> cancelable</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">DOMEventTarget currentTarget</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> defaultPrevented</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">number</span><span class="token plain"> eventPhase</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> isTrusted</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">void</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">preventDefault</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">void</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">stopPropagation</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">void</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">stopImmediatePropagation</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">DOMEventTarget target</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">number</span><span class="token plain"> timeStamp</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">string</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">type</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" 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_LjdS" 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></div><h4 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="12-react-合成事件">1.2 React 合成事件<a href="#12-react-合成事件" class="hash-link" aria-label="Direct link to 1.2 React 合成事件" title="Direct link to 1.2 React 合成事件"></a></h4><p>React 的事件机制中,在遵循规范的前提下,引入新的事件类型:合成事件(SyntheticEvent)。基于合成事件实现了浏览器中常见的用户事件,并对事件进行规范化处理,使它们在不同浏览器中具有一致的属性。</p><p>在事件发生时,相关信息会存储在 SyntheticEvent 的实例对象中,对象包含原生事件对象类似的属性。</p><div class="language-ts codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-ts codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">// SyntheticEvent 属性</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> bubbles</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> cancelable</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">DOMEventTarget currentTarget</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> defaultPrevented</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">number</span><span class="token plain"> eventPhase</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> isTrusted</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">DOMEvent nativeEvent</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">void</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">preventDefault</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">isDefaultPrevented</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">void</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">stopPropagation</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">boolean</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">isPropagationStopped</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">void</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">persist</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain">DOMEventTarget target</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">number</span><span class="token plain"> timeStamp</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token builtin">string</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">type</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" 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_LjdS" 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></div><p>但是合成事件与原生事件不是一一映射的关系。比如 onMouseEnter 合成事件映射原生 mouseout、mouseover 事件。React 通过 registrationNameDependencies 来记录合成事件和原生事件的映射关系:</p><div class="language-js codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-js codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">/**</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * Mapping from registration name to event name</span><br></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> */</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword module" style="color:#00009f">export</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> registrationNameDependencies </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><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">onClick</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">"click"</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">onMouseEnter</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">"mouseout"</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> </span><span class="token string" style="color:#e3116c">"mouseover"</span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token literal-property property" style="color:#36acaa">onChange</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><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token string" style="color:#e3116c">"change"</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 string" style="color:#e3116c">"click"</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 string" style="color:#e3116c">"focusin"</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 string" style="color:#e3116c">"focusout"</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 string" style="color:#e3116c">"input"</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 string" style="color:#e3116c">"keydown"</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 string" style="color:#e3116c">"keyup"</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 string" style="color:#e3116c">"selectionchange"</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">]</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// ...</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" 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_LjdS" 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></div><h3 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="2-react-事件机制">2. React 事件机制<a href="#2-react-事件机制" class="hash-link" aria-label="Direct link to 2. React 事件机制" title="Direct link to 2. React 事件机制"></a></h3><h4 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="21-react-事件的注册">2.1 React 事件的注册<a href="#21-react-事件的注册" class="hash-link" aria-label="Direct link to 2.1 React 事件的注册" title="Direct link to 2.1 React 事件的注册"></a></h4><p><img loading="lazy" src="https://user-images.githubusercontent.com/17002181/143735223-cb577bcf-8e4c-4047-8818-cbc28a1e8b69.png" class="img_ev3q"></p><p>使用 ReactDOM.createRoot 创建 Root 时,React 会调用 listenToAllSupportedEvents 方法对所有支持的原生事件进行监听:</p><ol><li>allNativeEvents 用于收集所有合成事件相关联的原生事件名。这个收集动作在事件插件初始化阶段完成;</li></ol><div class="language-js codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-js codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#393A34"><span class="token maybe-class-name">SimpleEventPlugin</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">registerEvents</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token maybe-class-name">EnterLeaveEventPlugin</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">registerEvents</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token maybe-class-name">ChangeEventPlugin</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">registerEvents</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token maybe-class-name">SelectEventPlugin</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">registerEvents</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token maybe-class-name">BeforeInputEventPlugin</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">registerEvents</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><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" 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_LjdS" 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></div><ol start="2"><li>对每个原生事件调用 addTrappedEventListener 函数。该函数最终使用 addEventListener 方法,对原生事件进行捕获或冒泡阶段的事件监听注册。</li></ol><div class="language-ts codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#393A34;--prism-background-color:#f6f8fa"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-ts codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><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">addTrappedEventListener</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"> targetContainer</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> EventTarget</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"> domEventName</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> DOMEventName</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"> eventSystemFlags</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> EventSystemFlags</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"> isCapturePhaseListener</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token builtin">boolean</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token 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">let</span><span class="token plain"> listener </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">createEventListenerWrapperWithPriority</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"> targetContainer</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"> domEventName</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"> eventSystemFlags</span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// ...</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">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">isCapturePhaseListener</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 function" style="color:#d73a49">addEventCaptureListener</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">targetContainer</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> domEventName</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> listener</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">else</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">addEventBubbleListener</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">targetContainer</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> domEventName</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> listener</span><span class="token punctuation" style="color:#393A34">)</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" 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_LjdS" 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></div><p>基于以上流程可知,调用 ReactDOM.createRoot 方法时,就已经在 root 节点上初始化所有原生事件的监听回调函数。而不是在组件上写合成事件的监听时,才开始注册事件回调。</p><h4 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="22-react-事件的触发">2.2 React 事件的触发<a href="#22-react-事件的触发" class="hash-link" aria-label="Direct link to 2.2 React 事件的触发" title="Direct link to 2.2 React 事件的触发"></a></h4><p><img loading="lazy" src="https://user-images.githubusercontent.com/17002181/144073503-a8a2eb15-a2e7-4d98-9f0e-ef2a6b5c0738.png" class="img_ev3q"></p><p>在注册事件阶段调用的 addTrappedEventListener 方法中,会使用 createEventListenerWrapperWithPriority 函数来创建事件回调。createEventListenerWrapperWithPriority 函数根据事件类型,划分出若干个不同优先级的 dispathEvent。事件回调最终都调用进 dispatchEvent 方法。</p><p>因此触发一个原生事件时,大致的执行流程如下:</p><ol><li>原生事件触发后,进入 dispatchEvent 回调方法;</li><li>attemptToDispatchEvent 方法根据该原生事件查找到当前原生 Dom 节点和映射的 Fiber 节点;</li><li>事件和 Fiber 等信息被派发给插件系统进行处理,插件系统调用各插件暴露的 extractEvents 方法;</li><li>accumulateSinglePhaseListeners 方法向上收集 Fiber 树上监听相关事件的其他回调函数,构造合成事件并加入到派发队列 dispatchQueue 中;</li><li>调用 processDispatchQueue 方法,基于捕获或冒泡阶段的标识,按倒序或顺序执行 dispatchQueue 中的方法;</li></ol><h2 class="anchor anchorWithHideOnScrollNavbar_WYt5" id="参考资料">参考资料<a href="#参考资料" class="hash-link" aria-label="Direct link to 参考资料" title="Direct link to 参考资料"></a></h2><ol><li><a href="https://reactjs.org/docs/events.html" target="_blank" rel="noopener noreferrer">SyntheticEvent</a></li><li><a href="https://reactjs.org/docs/handling-events.html" target="_blank" rel="noopener noreferrer">Handling Events</a></li><li><a href="https://www.w3.org/TR/DOM-Level-3-Events" target="_blank" rel="noopener noreferrer">UI Events</a></li></ol></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><a class="pagination-nav__link pagination-nav__link--prev" href="/awesome-interview/book4/engineer-mfa"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">工程化:谈谈微前端</div></a><a class="pagination-nav__link pagination-nav__link--next" href="/awesome-interview/book4/frame-react-vs-vue"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">框架:谈谈 React 和 Vue 的区别</div></a></nav></div></div><div class="col col--3"><div class="tableOfContents_bqdL 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-原生事件和合成事件" class="table-of-contents__link toc-highlight">1. 原生事件和合成事件</a><ul><li><a href="#11-原生事件" class="table-of-contents__link toc-highlight">1.1 原生事件</a></li><li><a href="#12-react-合成事件" class="table-of-contents__link toc-highlight">1.2 React 合成事件</a></li></ul></li><li><a href="#2-react-事件机制" class="table-of-contents__link toc-highlight">2. 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