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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>Vue 的数据绑定机制</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>Vue 是如何实现数据劫持的</li><li>Vue 是如何实现双向绑定的</li><li>MVVM 是什么</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>响应式对象</code> <code>数据劫持</code> <code>双向绑定</code> <code>MVVM（Model-View-ViewModel）</code> <code>发布/订阅模式（publish-subscribe pattern）</code></p><p><strong>响应式对象</strong></p><p>Vue2 通过 <code>Object.defineProperty</code>，Vue3 通过 Proxy 来劫持 state 中各个属性的 setter、getter，通过 getter 收集依赖。当 state 中的数据发生变动之后发布通知给订阅者更新数据。</p><p><strong>双向绑定</strong></p><p>Vue 通过 <code>v-model</code> 实现双向绑定。<code>v-model</code> 实际是 <code>v-bind:xxx</code> 和 <code>v-on:xxx</code> 的语法糖。当触发元素对应的事件（如 input、change 等）时更新数据（ViewModel），当数据（ViewModel）更新时同步更新到元素的对应属性（View）上。</p><p><strong>MVVM（Model-View-ViewModel）</strong></p><p>MVVM 模式是一种软件架构模式，相比 MVC 模式多了一个 ViewModel 层。有助于将图形用户界面的开发与业务逻辑或后端逻辑（数据模型）的开发分离开来。</p><ul><li>Model：模型层，负责处理业务逻辑以及和服务器端进行交互。</li><li>View：视图层，将数据通过 UI 展现出来。</li><li>ViewModel：视图模型层，连接 Model 层和 View 层。</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-前置概念"></a>1. 前置概念<a class="hash-link" href="#1-前置概念" title="Direct link to heading">#</a></h3><p>在详细说明原理之前，需要对以下概念有一定的认知：</p><ol><li>Dep：实现发布订阅模式的模块。</li><li>Watcher：订阅更新和触发视图更新的模块。</li></ol><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="2-实现原理"></a>2. 实现原理<a class="hash-link" href="#2-实现原理" title="Direct link to heading">#</a></h3><p><img src="https://user-images.githubusercontent.com/3984824/132991936-828bba61-2c87-4ee2-acf0-ffef294760fb.png" alt="image"></p><p>上图是 Vue 官网描述 Vue 内数据变化与发布更新的流程，我们以响应式对象、依赖收集、数据更新的顺序详细说明整个过程。</p><h4><a aria-hidden="true" tabindex="-1" class="anchor anchor__h4 anchorWithHideOnScrollNavbar_3R7-" id="21-响应式对象"></a>2.1 响应式对象<a class="hash-link" href="#21-响应式对象" title="Direct link to heading">#</a></h4><p>Vue2 通过 <code>Object.defineProperty</code>，Vue3 通过 Proxy 来劫持 state 中各个属性的 getter、setter。其中 getter 中主要是通过 Dep 收集依赖这个属性的订阅者，setter 中则是在属性变化后通知 Dep 收集到的订阅者，派发更新。</p><p>以下是 Dep 的伪代码：</p><div class="codeBlockContainer_K1bP"><div class="codeBlockContent_hGly typescript"><pre tabindex="0" class="prism-code language-typescript 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">export</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">default</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">class</span><span class="token plain"> </span><span class="token class-name maybe-class-name">Dep</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">static</span><span class="token plain"> target</span><span class="token operator" style="color:#393A34">?</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Watcher</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"> subs</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 maybe-class-name">Watcher</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" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">constructor</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">subs</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">[</span><span class="token punctuation" style="color:#393A34">]</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 添加订阅者（watcher）</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> **/</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">addSub</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">sub</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Watcher</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">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">subs</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">push</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">sub</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 移除订阅者（watcher）</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> **/</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">removeSub</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">sub</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Watcher</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 function" style="color:#d73a49">remove</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">subs</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> sub</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 添加订阅（调用订阅者上的 addDep 方法）</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> **/</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">depend</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token maybe-class-name">Dep</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">target</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 maybe-class-name">Dep</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">target</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">addDep</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">this</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 punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 遍历通知订阅者更新</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> **/</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">notify</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> subs </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">subs</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">slice</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">for</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">let</span><span class="token plain"> i </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"> l </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> subs</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">length</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> i </span><span class="token operator" style="color:#393A34"><</span><span class="token plain"> l</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"> i</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"> subs</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 method function property-access" style="color:#d73a49">update</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 punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token maybe-class-name">Dep</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">target</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">null</span></span></code></pre><button type="button" aria-label="Copy code to clipboard" class="copyButton_Ue-o clean-btn">Copy</button></div></div><p>以下是生成响应式对象的伪代码：</p><div class="codeBlockContainer_K1bP"><div class="codeBlockContent_hGly typescript"><pre tabindex="0" class="prism-code language-typescript codeBlock_23N8 thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_39YC"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 生成响应式对象</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 为了方便理解，以下代码略有修改，省略了部分不相关内容</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> */</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">export</span><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">defineReactive</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"> obj</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Object</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> key</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token builtin">string</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> val</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token builtin">any</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 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"> dep </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">new</span><span class="token plain"> </span><span class="token class-name maybe-class-name">Dep</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 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">defineProperty</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">obj</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> key</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"> enumerable</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"> configurable</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 function-variable function" style="color:#d73a49">get</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">reactiveGetter</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 每次 get 时如果有订阅者则添加订阅</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">if</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token maybe-class-name">Dep</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">target</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"> dep</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">depend</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">return</span><span class="token plain"> val</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function-variable function" style="color:#d73a49">set</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">function</span><span class="token plain"> </span><span class="token function" style="color:#d73a49">reactiveSetter</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">newVal</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"> val </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> newVal</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 每次更新数据之后广播更新</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> dep</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">notify</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 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="22-依赖收集"></a>2.2 依赖收集<a class="hash-link" href="#22-依赖收集" title="Direct link to heading">#</a></h4><p>Vue 会在需要使用到属性的地方新建一个 Watcher 的实例 watcher，watcher 实例化时会读取对应属性的内容，从而触发 1.1 中的 getter，将 watcher 注册进 Dep 中。</p><p>以下是 Watcher 的伪代码：</p><div class="codeBlockContainer_K1bP"><div class="codeBlockContent_hGly typescript"><pre tabindex="0" class="prism-code language-typescript codeBlock_23N8 thin-scrollbar" style="color:#393A34;background-color:#f6f8fa"><code class="codeBlockLines_39YC"><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 为了方便理解，以下代码略有修改，省略了部分不相关内容</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> */</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"></span><span class="token keyword" style="color:#00009f">export</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">default</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">class</span><span class="token plain"> </span><span class="token class-name maybe-class-name">Watcher</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"> vm</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Component</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"> getter</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> value</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token builtin">any</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"> cb</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token known-class-name class-name">Function</span><span class="token punctuation" style="color:#393A34">;</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">constructor</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"> vm</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Component</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"> exp</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token builtin">string</span><span class="token plain"></span></span><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></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">vm</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> vm</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">cb</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> cb</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 获取表达式对应的属性的 getter</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">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">getter</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">parsePath</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">exp</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">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">value</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token keyword" style="color:#00009f">get</span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 获取最新的值</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> **/</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">get</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">// 将 Dep 的当前订阅者指向当前 watcher</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">Dep</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">target</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token 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"> value</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"> vm </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">vm</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">// 获取对应属性值</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> value </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">getter</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">call</span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">vm</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> vm</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">// 清空 Dep 当前订阅者</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">Dep</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">target</span><span class="token plain"> </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">null</span><span class="token plain"></span></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"> value</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 订阅</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> **/</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">addDep</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token plain">dep</span><span class="token operator" style="color:#393A34">:</span><span class="token plain"> </span><span class="token maybe-class-name">Dep</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">// 将当前 watcher 添加到 Dep 的订阅者列表中</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> dep</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">addSub</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">}</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain" style="display:inline-block">
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</span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token comment" style="color:#999988;font-style:italic">/**</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> * 更新视图</span></span><span class="token-line" style="color:#393A34"><span class="token comment" style="color:#999988;font-style:italic"> **/</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token function" style="color:#d73a49">update</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">(</span><span class="token punctuation" style="color:#393A34">)</span><span class="token plain"> </span><span class="token punctuation" style="color:#393A34">{</span><span class="token plain"></span></span><span class="token-line" style="color:#393A34"><span class="token plain"> </span><span class="token keyword" style="color:#00009f">const</span><span class="token plain"> value </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token keyword" style="color:#00009f">get</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"> oldValue </span><span class="token operator" style="color:#393A34">=</span><span class="token plain"> </span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">value</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">// 调用 callback 更新视图</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">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">cb</span><span class="token punctuation" style="color:#393A34">.</span><span class="token method function property-access" style="color:#d73a49">call</span><span class="token punctuation" style="color:#393A34">(</span><span class="token keyword" style="color:#00009f">this</span><span class="token punctuation" style="color:#393A34">.</span><span class="token property-access">vm</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> value</span><span class="token punctuation" style="color:#393A34">,</span><span class="token plain"> oldValue</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 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="23-数据更新"></a>2.3 数据更新<a class="hash-link" href="#23-数据更新" title="Direct link to heading">#</a></h4><p>state 属性更新时会触发属性的 setter，setter 中会触发 Dep 的更新，Dep 通知 1.2 中收集到的 watcher 更新，watcher 获取到更新的数据之后触发更新视图。</p><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="3-无法监听到的变化"></a>3. 无法监听到的变化<a class="hash-link" href="#3-无法监听到的变化" title="Direct link to heading">#</a></h3><p>由于受到 JavaScript 设计的限制，Vue2 使用的 <code>Object.defineProperty</code> 并不能完全劫持所有数据的变化，以下是几种无法正常劫持的变化：</p><ul><li>无法劫持新创建的属性，为了解决这个问题，Vue 提供了 <code>Vue.set</code> 以创建新属性。</li><li>无法劫持数组的变化，为了解决这个问题，Vue 对数组原生方法进行了劫持。</li><li>无法劫持利用索引修改数组元素，这个问题同样可以用 <code>Vue.set</code> 解决。</li></ul><h3><a aria-hidden="true" tabindex="-1" class="anchor anchor__h3 anchorWithHideOnScrollNavbar_3R7-" id="4-vue2-与-vue3-的差异"></a>4. Vue2 与 Vue3 的差异<a class="hash-link" href="#4-vue2-与-vue3-的差异" title="Direct link to heading">#</a></h3><p>Vue2 与 Vue3 数据绑定机制的主要差异是劫持方式。Vue2 使用的是 <code>Object.defineProperty</code> 而 Vue3 使用的是 <code>Proxy</code>。<code>Proxy</code> 可以创建一个对象的代理，从而实现对这个对象基本操作的拦截和自定义。</p><table><thead><tr><th>特性</th><th>defineProperty</th><th>Proxy</th></tr></thead><tbody><tr><td>劫持新创建属性</td><td>否</td><td>是</td></tr><tr><td>劫持数组变化</td><td>否</td><td>是</td></tr><tr><td>劫持索引修改数组元素</td><td>否</td><td>是</td></tr><tr><td>兼容性</td><td>IE8及以上</td><td>不支持IE</td></tr></tbody></table><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://vuejs.org/" target="_blank" rel="noopener noreferrer">Vuejs 官网</a></li><li><a href="https://github.com/vuejs/vue" target="_blank" rel="noopener noreferrer">Vuejs 源码</a></li></ol></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Docs pages navigation"><div class="pagination-nav__item"><a class="pagination-nav__link" href="/awesome-interview/book1/engineer-webpack-workflow"><div class="pagination-nav__sublabel">Previous</div><div class="pagination-nav__label">« 工程化：Webpack 工作流程</div></a></div><div class="pagination-nav__item pagination-nav__item--next"><a class="pagination-nav__link" href="/awesome-interview/book1/frame-vue-computed-watch"><div class="pagination-nav__sublabel">Next</div><div class="pagination-nav__label">框架：Vue 的 computed 和 watch 的区别 »</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-前置概念" class="table-of-contents__link">1. 前置概念</a></li><li><a href="#2-实现原理" class="table-of-contents__link">2. 实现原理</a></li><li><a href="#3-无法监听到的变化" class="table-of-contents__link">3. 无法监听到的变化</a></li><li><a href="#4-vue2-与-vue3-的差异" class="table-of-contents__link">4. Vue2 与 Vue3 的差异</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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