ZiuChen.github.io/assets/note_React.md.37738659.js

import{_ as s,o as n,c as a,a as l}from"./app.ab8d0b9f.js";const C=JSON.parse('{"title":"React","description":"","frontmatter":{},"headers":[{"level":2,"title":"邂逅React","slug":"邂逅react","link":"#邂逅react","children":[{"level":3,"title":"React开发依赖","slug":"react开发依赖","link":"#react开发依赖","children":[]},{"level":3,"title":"Babel与React的关系","slug":"babel与react的关系","link":"#babel与react的关系","children":[]},{"level":3,"title":"React初体验","slug":"react初体验","link":"#react初体验","children":[]},{"level":3,"title":"第一个React程序","slug":"第一个react程序","link":"#第一个react程序","children":[]},{"level":3,"title":"组件化开发","slug":"组件化开发","link":"#组件化开发","children":[]},{"level":3,"title":"提前绑定this","slug":"提前绑定this","link":"#提前绑定this","children":[]}]}],"relativePath":"note/React.md","lastUpdated":1681490337000}'),p={name:"note/React.md"},e=l(`<h1 id="react" tabindex="-1">React <a class="header-anchor" href="#react" aria-hidden="true">#</a></h1><h2 id="邂逅react" tabindex="-1">邂逅React <a class="header-anchor" href="#邂逅react" aria-hidden="true">#</a></h2><h3 id="react开发依赖" tabindex="-1">React开发依赖 <a class="header-anchor" href="#react开发依赖" aria-hidden="true">#</a></h3><ul><li><code>react</code> 包含React的核心代码</li><li><code>react-dom</code> 将React渲染到不同平台需要的核心代码</li><li><code>babel</code> 将JSX转换成React代码的工具</li></ul><p>为什么要拆分成这么多的包？</p><ul><li>不同的库各司其职，让库变得纯粹</li><li><code>react</code>包中包含了 React Web 和 React Native 共同拥有的<strong>核心代码</strong></li><li><code>react-dom</code> 针对Web和Native完成的事情不同 <ul><li>Web端：<code>react-dom</code>会将JSX渲染成真实DOM，展示在浏览器中</li><li>Native端：<code>react-dom</code>会将JSX渲染成原生的控件（如Android中的Button，iOS中的UIButton）</li></ul></li></ul><h3 id="babel与react的关系" tabindex="-1">Babel与React的关系 <a class="header-anchor" href="#babel与react的关系" aria-hidden="true">#</a></h3><p>Babel是什么？</p><ul><li>Babel又名Babel.js</li><li>是目前前端使用非常广泛的编译器、转换器（Compiler/Transformer）</li><li>提供对ES6语法的Polyfill，将ES6语法转为大多数浏览器都支持的ES5语法</li></ul><p>二者之间的联系</p><ul><li>默认情况下React开发可以不使用Babel</li><li>但是我们不可能使用React.createElement来编写代码</li><li>通过Babel，我们可以直接编写JSX（JavaScript XML），让Babel帮我们转化为React.createElement</li></ul><h3 id="react初体验" tabindex="-1">React初体验 <a class="header-anchor" href="#react初体验" aria-hidden="true">#</a></h3><p>我们通过CDN方式引入react、react-dom、babel这三个依赖</p><p>并且创建<code>#root</code>根节点，作为渲染React组件的容器，再新建一个script标签，键入以下内容</p><div class="language-html line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">html</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">id</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">root</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">&gt;&lt;/</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">script</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">src</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">https://unpkg.com/react@18/umd/react.development.js</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">crossorigin</span><span style="color:#89DDFF;">&gt;&lt;/</span><span style="color:#F07178;">script</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">script</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">src</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">https://unpkg.com/react-dom@18/umd/react-dom.development.js</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">crossorigin</span><span style="color:#89DDFF;">&gt;&lt;/</span><span style="color:#F07178;">script</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">script</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">src</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">https://unpkg.com/babel-standalone@6/babel.min.js</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">crossorigin</span><span style="color:#89DDFF;">&gt;&lt;/</span><span style="color:#F07178;">script</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">script</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">type</span><span style="color:#89DDFF;">=</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">text/babel</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">  ReactDOM</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">render</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;">Hello, React!</span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;,</span><span style="color:#A6ACCD;"> document</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">querySelector</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">#root</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">script</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>这时，一个内容为<code>Hello, React!</code>的div标签就被渲染到页面上了</p><p>需要注意的是：<code>ReactDOM.render</code>这种写法适用于React18之前，在React18之后建议用下面的代码渲染根节点：</p><div class="language-tsx line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">tsx</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> root </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> ReactDOM</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">createRoot</span><span style="color:#A6ACCD;">(document</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">querySelector</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">#root</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"><span style="color:#A6ACCD;">root</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">render</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">h1</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;">Hello, React!</span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">h1</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="第一个react程序" tabindex="-1">第一个React程序 <a class="header-anchor" href="#第一个react程序" aria-hidden="true">#</a></h3><p>设想我们现在有这样一个需求：点击按钮使文本<code>Hello, World!</code>变为<code>Hello, React!</code></p><p>我们很容易就能写出如下代码：</p><div class="language-tsx line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">tsx</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> root </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> ReactDOM</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">createRoot</span><span style="color:#A6ACCD;">(document</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">querySelector</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">#root</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> msg </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, World!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#82AAFF;">render</span><span style="color:#A6ACCD;">() </span><span style="color:#676E95;font-style:italic;">// initial render</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">function</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">handleChangeClick</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#A6ACCD;">msg</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, React!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#A6ACCD;">root</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">render</span><span style="color:#A6ACCD;">(</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">h1</span><span style="color:#89DDFF;">&gt;{</span><span style="color:#A6ACCD;">msg</span><span style="color:#89DDFF;">}&lt;/</span><span style="color:#F07178;">h1</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">onClick</span><span style="color:#89DDFF;">={</span><span style="color:#A6ACCD;">handleChangeClick</span><span style="color:#89DDFF;">}&gt;</span><span style="color:#A6ACCD;">Change Text</span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br></div></div><p>在Vue中，如果我们对数据进行了修改，Vue的数据响应式会自动帮我们完成视图的更新</p><p>然而在React中，当我们修改了数据需要通知React，让React重新渲染视图。在这里，我们可以把渲染的过程封装为一个函数，方便我们重复调用，触发重新渲染</p><div class="language-tsx line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">tsx</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> root </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> ReactDOM</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">createRoot</span><span style="color:#A6ACCD;">(document</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">querySelector</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">#root</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> msg </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, World!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"></span>
<span class="line"><span style="color:#82AAFF;">render</span><span style="color:#A6ACCD;">() </span><span style="color:#676E95;font-style:italic;">// initial render</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">function</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">handleChangeClick</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#A6ACCD;">msg</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, React!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#82AAFF;">render</span><span style="color:#F07178;">() </span><span style="color:#676E95;font-style:italic;">// re-render</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">function</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">render</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#A6ACCD;">root</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">render</span><span style="color:#F07178;">(</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">      </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">h1</span><span style="color:#89DDFF;">&gt;{</span><span style="color:#A6ACCD;">msg</span><span style="color:#89DDFF;">}&lt;/</span><span style="color:#F07178;">h1</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">      </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">onClick</span><span style="color:#89DDFF;">={</span><span style="color:#A6ACCD;">handleChangeClick</span><span style="color:#89DDFF;">}&gt;</span><span style="color:#A6ACCD;">Change Text</span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#F07178;">  )</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div><p>这个案例中，我们使用<code>{}</code>语法，将动态的JS语法嵌入到JSX代码中</p><h3 id="组件化开发" tabindex="-1">组件化开发 <a class="header-anchor" href="#组件化开发" aria-hidden="true">#</a></h3><p>React有两种组件：类组件与函数组件，React18+推荐使用函数组件+Hooks</p><h4 id="类组件" tabindex="-1">类组件 <a class="header-anchor" href="#类组件" aria-hidden="true">#</a></h4><p>我们使用类组件来逐步重构上面的案例：</p><div class="language-tsx line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">tsx</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#C792EA;">class</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">App</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">extends</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">React</span><span style="color:#89DDFF;">.</span><span style="color:#FFCB6B;">Component</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#C792EA;">constructor</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#A6ACCD;">super</span><span style="color:#F07178;">()</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">this.</span><span style="color:#A6ACCD;">state</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">      msg</span><span style="color:#89DDFF;">:</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, World!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#F07178;">render</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;font-style:italic;">return</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">h2</span><span style="color:#89DDFF;">&gt;{this.</span><span style="color:#A6ACCD;">state</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">msg</span><span style="color:#89DDFF;">}&lt;/</span><span style="color:#F07178;">h2</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> root </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> ReactDOM</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">createRoot</span><span style="color:#A6ACCD;">(document</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">querySelector</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">#root</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"><span style="color:#A6ACCD;">root</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">render</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&lt;</span><span style="color:#FFCB6B;">App</span><span style="color:#89DDFF;"> /&gt;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><ul><li><p>类组件必须实现render方法，render方法返回值为后续React渲染到页面的内容</p></li><li><p>组件内数据分为两类</p><ul><li>参与页面更新的数据 <ul><li>当数据变化时，需要触发组件重新渲染</li></ul></li><li>不参与页面更新的数据 <ul><li>数据不会变化，或变化后也不需要重新渲染视图</li></ul></li></ul></li><li><p>需要触发视图重新渲染的数据，我们将其成为：<strong>参与数据流</strong></p><ul><li>定义在对象的<code>state</code>属性中</li><li>可以通过在构造函数中通过 <code>this.state = { name: &#39;Ziu&#39; }</code> 来定义状态</li><li>当数据发生变化，可以调用 <code>this.setState</code> 来更新数据，通知React执行视图更新</li><li>update操作时，会重新调用render函数，使用最新的数据来渲染界面</li></ul></li></ul><p>:::success 需要注意的是，在constructor中我们调用了<code>super</code>，因为App类是继承自React.Component类，调用<code>super</code>即调用了其父类的构造函数，让我们的App组件可以继承一些内置属性/方法如<code>state setState render</code> :::</p><p>至此我们完成了数据的迁移，下面我们来完成事件函数的迁移。</p><p>有了之前的介绍，我们很容易的可以写出下面的代码：</p><div class="language-tsx line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">tsx</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#C792EA;">class</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">App</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">extends</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">React</span><span style="color:#89DDFF;">.</span><span style="color:#FFCB6B;">Component</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#C792EA;">constructor</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#A6ACCD;">super</span><span style="color:#F07178;">()</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">this.</span><span style="color:#A6ACCD;">state</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">      msg</span><span style="color:#89DDFF;">:</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, World!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#F07178;">changeText</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">this.</span><span style="color:#82AAFF;">setState</span><span style="color:#F07178;">(</span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">      msg</span><span style="color:#89DDFF;">:</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, React!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span><span style="color:#F07178;">)</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#F07178;">render</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;font-style:italic;">return</span><span style="color:#F07178;"> (</span></span>
<span class="line"><span style="color:#F07178;">      </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">h2</span><span style="color:#89DDFF;">&gt;{this.</span><span style="color:#A6ACCD;">state</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">msg</span><span style="color:#89DDFF;">}&lt;/</span><span style="color:#F07178;">h2</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">onClick</span><span style="color:#89DDFF;">={this.</span><span style="color:#A6ACCD;">changeText</span><span style="color:#89DDFF;">}&gt;</span><span style="color:#A6ACCD;">Change Text</span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">      </span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#F07178;">    )</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> root </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> ReactDOM</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">createRoot</span><span style="color:#A6ACCD;">(document</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">querySelector</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">#root</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"><span style="color:#A6ACCD;">root</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">render</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&lt;</span><span style="color:#FFCB6B;">App</span><span style="color:#89DDFF;"> /&gt;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br></div></div><p>我们可以写一个实例方法changeText来修改msg，然而此时changeText函数是不会正常工作的，我们在changeText中打log发现函数被正常触发了</p><p>为什么this.setState失效了？这和this的绑定有关：绑定的<code>changeText</code>在被调用时，向上找<code>this</code>找到的是<code>undefined</code></p><p>举一个类似情况的例子：</p><div class="language-ts line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">ts</span><pre class="shiki material-theme-palenight"><code><span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> app </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">new</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">App</span><span style="color:#A6ACCD;">()</span></span>
<span class="line"><span style="color:#A6ACCD;">app</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">changeText</span><span style="color:#A6ACCD;">() </span><span style="color:#676E95;font-style:italic;">// this =&gt; app</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> func </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> app</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">changeText</span></span>
<span class="line"><span style="color:#82AAFF;">func</span><span style="color:#A6ACCD;">() </span><span style="color:#676E95;font-style:italic;">// this =&gt; undefined</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>在非严格模式下，直接调用func时的this指向的是window，严格模式下则为undefined</p><p>为了解决this绑定的问题，我们需要显式把函数调用绑定给当前组件，这时组件就可以正常工作了。</p><div class="language-tsx line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">tsx</span><pre class="shiki material-theme-palenight has-highlighted-lines"><code><span class="line"><span style="color:#C792EA;">class</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">App</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">extends</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">React</span><span style="color:#89DDFF;">.</span><span style="color:#FFCB6B;">Component</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#C792EA;">constructor</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#A6ACCD;">super</span><span style="color:#F07178;">()</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">this.</span><span style="color:#A6ACCD;">state</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">      msg</span><span style="color:#89DDFF;">:</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, World!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#F07178;">changeText</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">this.</span><span style="color:#82AAFF;">setState</span><span style="color:#F07178;">(</span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">      msg</span><span style="color:#89DDFF;">:</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, React!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">}</span><span style="color:#F07178;">)</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">  </span><span style="color:#F07178;">render</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;font-style:italic;">return</span><span style="color:#F07178;"> (</span></span>
<span class="line"><span style="color:#F07178;">      </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">h2</span><span style="color:#89DDFF;">&gt;{this.</span><span style="color:#A6ACCD;">state</span><span style="color:#89DDFF;">.</span><span style="color:#A6ACCD;">msg</span><span style="color:#89DDFF;">}&lt;/</span><span style="color:#F07178;">h2</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line highlighted"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">onClick</span><span style="color:#89DDFF;">={this.</span><span style="color:#A6ACCD;">changeText</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">bind</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">this</span><span style="color:#A6ACCD;">)</span><span style="color:#89DDFF;">}&gt;</span><span style="color:#A6ACCD;">Change Text</span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#A6ACCD;">      </span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">div</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#F07178;">    )</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span>
<span class="line"><span style="color:#C792EA;">const</span><span style="color:#A6ACCD;"> root </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> ReactDOM</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">createRoot</span><span style="color:#A6ACCD;">(document</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">querySelector</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">#root</span><span style="color:#89DDFF;">&#39;</span><span style="color:#A6ACCD;">))</span></span>
<span class="line"><span style="color:#A6ACCD;">root</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">render</span><span style="color:#A6ACCD;">(</span><span style="color:#89DDFF;">&lt;</span><span style="color:#FFCB6B;">App</span><span style="color:#89DDFF;"> /&gt;</span><span style="color:#A6ACCD;">)</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br></div></div><h3 id="提前绑定this" tabindex="-1">提前绑定this <a class="header-anchor" href="#提前绑定this" aria-hidden="true">#</a></h3><p>在render函数中频繁通过<code>.bind</code>毕竟不太优雅，好在也有另一种方式：可以在constructor中提前对实例方法进行this绑定：</p><div class="language-tsx line-numbers-mode"><button title="Copy Code" class="copy"></button><span class="lang">tsx</span><pre class="shiki material-theme-palenight has-highlighted-lines"><code><span class="line"><span style="color:#89DDFF;">...</span></span>
<span class="line"><span style="color:#82AAFF;">constructor</span><span style="color:#A6ACCD;">() </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#A6ACCD;">super</span><span style="color:#F07178;">()</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">this.</span><span style="color:#A6ACCD;">state</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">    msg</span><span style="color:#89DDFF;">:</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">&#39;</span><span style="color:#C3E88D;">Hello, World!</span><span style="color:#89DDFF;">&#39;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">}</span></span>
<span class="line highlighted"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">this.</span><span style="color:#A6ACCD;">changeText</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">=</span><span style="color:#F07178;"> </span><span style="color:#89DDFF;">this.</span><span style="color:#A6ACCD;">changeText</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">bind</span><span style="color:#F07178;">(</span><span style="color:#89DDFF;">this</span><span style="color:#F07178;">)</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#82AAFF;">render</span><span style="color:#A6ACCD;">() </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">...</span></span>
<span class="line"><span style="color:#F07178;">    </span><span style="color:#89DDFF;">&lt;</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;"> </span><span style="color:#C792EA;">onClick</span><span style="color:#89DDFF;">={this.</span><span style="color:#A6ACCD;">changeText</span><span style="color:#89DDFF;">}&gt;</span><span style="color:#A6ACCD;">Change Text</span><span style="color:#89DDFF;">&lt;/</span><span style="color:#F07178;">button</span><span style="color:#89DDFF;">&gt;</span></span>
<span class="line"><span style="color:#F07178;">  </span><span style="color:#89DDFF;">...</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#89DDFF;">...</span></span>
<span class="line"></span></code></pre><div class="line-numbers-wrapper" aria-hidden="true"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div>`,46),o=[e];function t(c,r,F,D,y,i){return n(),a("div",null,o)}const b=s(p,[["render",t]]);export{C as __pageData,b as default};