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  19.   <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="前端" class="dropdown-title"><a href="/blog/web/" class="link-title">前端</a> <span class="title" style="display:none;">前端</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><h4>前端文章</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/blog/pages/8143cc480faf9a11/" class="nav-link">JavaScript</a></li></ul></li><li class="dropdown-item"><h4>学习笔记</h4> <ul class="dropdown-subitem-wrapper"><li class="dropdown-subitem"><a href="/blog/note/javascript/" class="nav-link">《JavaScript教程》</a></li><li class="dropdown-subitem"><a href="/blog/note/js/" class="nav-link">《JavaScript高级程序设计》</a></li><li class="dropdown-subitem"><a href="/blog/note/es6/" class="nav-link">《ES6 教程》</a></li><li class="dropdown-subitem"><a href="/blog/note/vue/" class="nav-link">《Vue》</a></li><li class="dropdown-subitem"><a href="/blog/note/react/" class="nav-link">《React》</a></li><li class="dropdown-subitem"><a href="/blog/note/typescript-axios/" class="nav-link">《TypeScript 从零实现 axios》</a></li><li class="dropdown-subitem"><a href="/blog/note/git/" class="nav-link">《Git》</a></li><li class="dropdown-subitem"><a href="/blog/pages/51afd6/" class="nav-link">TypeScript</a></li><li class="dropdown-subitem"><a href="/blog/pages/4643cd/" class="nav-link">JS设计模式总结</a></li></ul></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="页面" class="dropdown-title"><a href="/blog/ui/" class="link-title">页面</a> <span class="title" style="display:none;">页面</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/pages/8309a5b876fc95e3/" class="nav-link">HTML</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/0a83b083bdf257cb/" class="nav-link">CSS</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="技术" class="dropdown-title"><a href="/blog/technology/" class="link-title">技术</a> <span class="title" style="display:none;">技术</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/pages/9a7ee40fc232253e/" class="nav-link">技术文档</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/4c778760be26d8b3/" class="nav-link">GitHub技巧</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/117708e0af7f0bd9/" class="nav-link">Nodejs</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/41f87d890d0a02af/" class="nav-link">博客搭建</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="更多" class="dropdown-title"><a href="/blog/more/" class="link-title">更多</a> <span class="title" style="display:none;">更多</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/pages/f2a556/" class="nav-link">学习</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/aea6571b7a8bae86/" class="nav-link">面试</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/2d615df9a36a98ed/" class="nav-link">心情杂货</a></li><li class="dropdown-item"><!----> <a href="/blog/pages/baaa02/" class="nav-link">实用技巧</a></li><li class="dropdown-item"><!----> <a href="/blog/friends/" class="nav-link">友情链接</a></li></ul></div></div><div class="nav-item"><a href="/blog/about/" class="nav-link">关于</a></div><div class="nav-item"><a href="/blog/pages/beb6c0bd8a66cea6/" class="nav-link">收藏</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="索引" class="dropdown-title"><a href="/blog/archives/" class="link-title">索引</a> <span class="title" style="display:none;">索引</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/blog/categories/" class="nav-link">分类</a></li><li class="dropdown-item"><!----> <a href="/blog/tags/" class="nav-link">标签</a></li><li class="dropdown-item"><!----> <a href="/blog/archives/" class="nav-link">归档</a></li></ul></div></div> <a href="https://github.com/heBody/blog" target="_blank" rel="noopener noreferrer" class="repo-link">
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  22.   个人游戏网站
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    24. 

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  25.     <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></nav>  <ul class="sidebar-links"><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>核心概念</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>高级指引</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Hook</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>案例演示</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/blog/pages/87146f/" aria-current="page" class="active sidebar-link">案例演示</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level2"><a href="/blog/pages/87146f/#案例代码" class="sidebar-link">案例代码</a></li><li class="sidebar-sub-header level2"><a href="/blog/pages/87146f/#为什么不可变性在-react-中非常重要" class="sidebar-link">为什么不可变性在 React 中非常重要</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/blog/pages/87146f/#直接修改数据" class="sidebar-link">直接修改数据</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/87146f/#新数据替换旧数据" class="sidebar-link">新数据替换旧数据</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/87146f/#简化复杂的功能" class="sidebar-link">简化复杂的功能</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/87146f/#跟踪数据的改变" class="sidebar-link">跟踪数据的改变</a></li><li class="sidebar-sub-header level4"><a href="/blog/pages/87146f/#" class="sidebar-link"></a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/87146f/#确定在-react-中何时重新渲染" class="sidebar-link">确定在 React 中何时重新渲染</a></li><li class="sidebar-sub-header level3"><a href="/blog/pages/87146f/#-2" class="sidebar-link"></a></li></ul></li></ul></li></ul></section></li></ul> </aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-06970110><div class="articleInfo" data-v-06970110><ul class="breadcrumbs" data-v-06970110><li data-v-06970110><a href="/blog/" title="首页" class="iconfont icon-home router-link-active" data-v-06970110></a></li> <li data-v-06970110><a href="/blog/note/react/#《React》笔记" data-v-06970110>《React》笔记</a></li><li data-v-06970110><a href="/blog/note/react/#案例演示" data-v-06970110>案例演示</a></li></ul> <div class="info" data-v-06970110><div title="作者" class="author iconfont icon-touxiang" data-v-06970110><a href="https://github.com/heBody" target="_blank" title="作者" class="beLink" data-v-06970110>heBody</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-06970110><a href="javascript:;" data-v-06970110>2021-03-27</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="data:image/png;base64,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">案例演示<!----></h1>  <div class="theme-vdoing-content content__default"><h1 id="案例演示"><a href="#案例演示" class="header-anchor">#</a> 案例演示</h1> <p>本节内容根据官方文档的 <a href="https://zh-hans.reactjs.org/tutorial/tutorial.html" target="_blank" rel="noopener noreferrer">教程<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> 编写。</p> <p><a href="https://codepen.io/gaearon/pen/gWWZgR?editors=0010" target="_blank" rel="noopener noreferrer">在线demo<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></p> <h2 id="案例代码"><a href="#案例代码" class="header-anchor">#</a> 案例代码</h2> <div class="language-jsx line-numbers-mode"><pre class="language-jsx"><code><span class="token keyword">import</span> React <span class="token keyword">from</span> <span class="token string">'react'</span>
    26. 

  26. <span class="token keyword">import</span> ReactDOM <span class="token keyword">from</span> <span class="token string">'react-dom'</span>
    27. 

  27. <span class="token keyword">import</span> <span class="token string">'./index.css'</span>
    28. 

  28. 

  29. <span class="token comment">// 正方形格子 (没有state时可以使用函数组件)</span>
    30. 

  30. <span class="token keyword">function</span> <span class="token function">Square</span> <span class="token punctuation">(</span><span class="token parameter">props</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    31. 

  31.   <span class="token comment">// return 返回一个React元素</span>
    32. 

  32.   <span class="token keyword">return</span> <span class="token punctuation">(</span>
    33. 

  33.     <span class="token comment">// &lt;button&gt; 是内置组件，onClick属性是内置组件内规定的点击方法</span>
    34. 

  34.     <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>button</span>
    35. 

  35.       <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>square<span class="token punctuation">&quot;</span></span>
    36. 

  36.       <span class="token attr-name">onClick</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span>props<span class="token punctuation">.</span>onClick<span class="token punctuation">}</span></span>
    37. 

  37.     <span class="token punctuation">&gt;</span></span><span class="token plain-text">
    38. 

  38.       </span><span class="token punctuation">{</span>props<span class="token punctuation">.</span>value<span class="token punctuation">}</span><span class="token plain-text">
    39. 

  39.     </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>button</span><span class="token punctuation">&gt;</span></span>
    40. 

  40.   <span class="token punctuation">)</span>
    41. 

  41. <span class="token punctuation">}</span>
    42. 

  42. 

  43. <span class="token comment">// `棋盘`组件（格子集合）</span>
    44. 

  44. <span class="token keyword">class</span> <span class="token class-name">Board</span> <span class="token keyword">extends</span> <span class="token class-name">React<span class="token punctuation">.</span>Component</span> <span class="token punctuation">{</span>
    45. 

  45.   <span class="token function">renderSquare</span> <span class="token punctuation">(</span><span class="token parameter">i</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    46. 

  46.     <span class="token comment">// 加小括号是防止自动添加分号而破坏结构</span>
    47. 

  47.     <span class="token keyword">return</span> <span class="token punctuation">(</span>
    48. 

  48.       <span class="token comment">// 向Square组件传递了两个参数 value 和 onClick</span>
    49. 

  49.       <span class="token comment">// 注意：这里的onClick是传参，而不是直接绑定点击事件</span>
    50. 

  50.       <span class="token comment">// 事件命名规范：on[Event]={ this.handle[Event] }</span>
    51. 

  51.       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span><span class="token class-name">Square</span></span>
    52. 

  52.         <span class="token attr-name">value</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span>props<span class="token punctuation">.</span>squares<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">}</span></span>
    53. 

  53.         <span class="token attr-name">onClick</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token keyword">this</span><span class="token punctuation">.</span>props<span class="token punctuation">.</span><span class="token function">onClick</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">}</span></span>
    54. 

  54.       <span class="token punctuation">/&gt;</span></span>
    55. 

  55.     <span class="token punctuation">)</span>
    56. 

  56.   <span class="token punctuation">}</span>
    57. 

  57. 

  58.   <span class="token comment">// render 方法描述你想在屏幕看到的内容</span>
    59. 

  59.   <span class="token function">render</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    60. 

  60.     <span class="token keyword">return</span> <span class="token punctuation">(</span>
    61. 

  61.       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    62. 

  62.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>board-row<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    63. 

  63.           </span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">renderSquare</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">}</span><span class="token plain-text">
    64. 

  64.           </span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">renderSquare</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">}</span><span class="token plain-text">
    65. 

  65.           </span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">renderSquare</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">}</span><span class="token plain-text">
    66. 

  66.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    67. 

  67.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>board-row<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    68. 

  68.           </span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">renderSquare</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">)</span><span class="token punctuation">}</span><span class="token plain-text">
    69. 

  69.           </span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">renderSquare</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">}</span><span class="token plain-text">
    70. 

  70.           </span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">renderSquare</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">}</span><span class="token plain-text">
    71. 

  71.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    72. 

  72.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>board-row<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    73. 

  73.           </span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">renderSquare</span><span class="token punctuation">(</span><span class="token number">6</span><span class="token punctuation">)</span><span class="token punctuation">}</span><span class="token plain-text">
    74. 

  74.           </span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">renderSquare</span><span class="token punctuation">(</span><span class="token number">7</span><span class="token punctuation">)</span><span class="token punctuation">}</span><span class="token plain-text">
    75. 

  75.           </span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">renderSquare</span><span class="token punctuation">(</span><span class="token number">8</span><span class="token punctuation">)</span><span class="token punctuation">}</span><span class="token plain-text">
    76. 

  76.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    77. 

  77.       </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
    78. 

  78.     <span class="token punctuation">)</span>
    79. 

  79.   <span class="token punctuation">}</span>
    80. 

  80. <span class="token punctuation">}</span>
    81. 

  81. 

  82. <span class="token comment">// `棋盘游戏`组件（最外层）</span>
    83. 

  83. <span class="token keyword">class</span> <span class="token class-name">Game</span> <span class="token keyword">extends</span> <span class="token class-name">React<span class="token punctuation">.</span>Component</span> <span class="token punctuation">{</span>
    84. 

  84.   <span class="token function">constructor</span><span class="token punctuation">(</span><span class="token parameter">props</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    85. 

  85.     <span class="token comment">// JavaScript class 继承中的构造函数内必需以super开头</span>
    86. 

  86.     <span class="token keyword">super</span><span class="token punctuation">(</span>props<span class="token punctuation">)</span>
    87. 

  87.     <span class="token comment">// state 是当前组件私有的</span>
    88. 

  88.     <span class="token keyword">this</span><span class="token punctuation">.</span>state <span class="token operator">=</span> <span class="token punctuation">{</span>
    89. 

  89.       <span class="token literal-property property">history</span><span class="token operator">:</span> <span class="token punctuation">[</span>
    90. 

  90.         <span class="token punctuation">{</span>
    91. 

  91.           <span class="token literal-property property">squares</span><span class="token operator">:</span> <span class="token function">Array</span><span class="token punctuation">(</span><span class="token number">9</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">fill</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">)</span>
    92. 

  92.         <span class="token punctuation">}</span>
    93. 

  93.       <span class="token punctuation">]</span><span class="token punctuation">,</span>
    94. 

  94.       <span class="token literal-property property">stepNumber</span><span class="token operator">:</span> <span class="token number">0</span><span class="token punctuation">,</span> <span class="token comment">// 当前正在查看的历史记录</span>
    95. 

  95.       <span class="token literal-property property">xIsNext</span><span class="token operator">:</span> <span class="token boolean">true</span><span class="token punctuation">,</span>
    96. 

  96.     <span class="token punctuation">}</span>
    97. 

  97.   <span class="token punctuation">}</span>
    98. 

  98. 

  99.   <span class="token comment">// 处理格子点击（由子组件触发）</span>
    100. 

  100.   <span class="token function">handleClick</span> <span class="token punctuation">(</span><span class="token parameter">i</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    101. 

  101.     <span class="token comment">// 这里的slice方法在`回到过去`时，会在副本中把`未来`历史记录丢弃掉，当setState时会抹去原来的`未来`记录。</span>
    102. 

  102.     <span class="token keyword">const</span> history <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>history<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token keyword">this</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>stepNumber <span class="token operator">+</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    103. 

  103.     <span class="token keyword">const</span> current <span class="token operator">=</span> history<span class="token punctuation">[</span>history<span class="token punctuation">.</span>length <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">]</span>
    104. 

  104.     <span class="token keyword">const</span> squares <span class="token operator">=</span> current<span class="token punctuation">.</span>squares<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// slice() 取数组副本</span>
    105. 

  105. 

  106.     <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token function">calculateWinner</span><span class="token punctuation">(</span>squares<span class="token punctuation">)</span> <span class="token operator">||</span> squares<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 当有获胜者 或 当前格子已落棋</span>
    107. 

  107.       <span class="token keyword">return</span><span class="token punctuation">;</span>
    108. 

  108.     <span class="token punctuation">}</span>
    109. 

  109.     squares<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>xIsNext <span class="token operator">?</span> <span class="token string">'X'</span> <span class="token operator">:</span> <span class="token string">'O'</span>
    110. 

  110.     <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    111. 

  111.       <span class="token comment">// concat不会改变原数组，而push会改变原数组</span>
    112. 

  112.       <span class="token literal-property property">history</span><span class="token operator">:</span> history<span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span><span class="token punctuation">[</span><span class="token punctuation">{</span>
    113. 

  113.         squares
    114. 

  114.       <span class="token punctuation">}</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
    115. 

  115.       <span class="token literal-property property">stepNumber</span><span class="token operator">:</span> history<span class="token punctuation">.</span>length<span class="token punctuation">,</span>
    116. 

  116.       <span class="token literal-property property">xIsNext</span><span class="token operator">:</span> <span class="token operator">!</span><span class="token keyword">this</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>xIsNext
    117. 

  117.     <span class="token punctuation">}</span><span class="token punctuation">)</span>
    118. 

  118.   <span class="token punctuation">}</span>
    119. 

  119. 

  120.   <span class="token comment">// 跳转历史步骤</span>
    121. 

  121.   <span class="token function">jumpTo</span> <span class="token punctuation">(</span><span class="token parameter">step</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    122. 

  122.     <span class="token comment">// 这里并未修改history</span>
    123. 

  123.     <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">setState</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    124. 

  124.       <span class="token literal-property property">stepNumber</span><span class="token operator">:</span> step<span class="token punctuation">,</span>
    125. 

  125.       <span class="token literal-property property">xIsNext</span><span class="token operator">:</span> <span class="token punctuation">(</span>step <span class="token operator">%</span> <span class="token number">2</span><span class="token punctuation">)</span> <span class="token operator">===</span> <span class="token number">0</span>
    126. 

  126.     <span class="token punctuation">}</span><span class="token punctuation">)</span>
    127. 

  127.   <span class="token punctuation">}</span>
    128. 

  128. 

  129.   <span class="token function">render</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    130. 

  130.     <span class="token keyword">const</span> history <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>history
    131. 

  131.     <span class="token keyword">const</span> current <span class="token operator">=</span> history<span class="token punctuation">[</span><span class="token keyword">this</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>stepNumber<span class="token punctuation">]</span>
    132. 

  132.     <span class="token keyword">const</span> winner <span class="token operator">=</span> <span class="token function">calculateWinner</span><span class="token punctuation">(</span>current<span class="token punctuation">.</span>squares<span class="token punctuation">)</span>
    133. 

  133. 

  134.     <span class="token comment">// 历史步骤 （map方法把原数组映射为另一个数组）</span>
    135. 

  135.     <span class="token keyword">const</span> moves <span class="token operator">=</span> history<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">step<span class="token punctuation">,</span> move</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
    136. 

  136.       <span class="token keyword">const</span> desc <span class="token operator">=</span> move <span class="token operator">?</span>
    137. 

  137.         <span class="token string">'Go to move #'</span> <span class="token operator">+</span> move <span class="token operator">:</span>
    138. 

  138.         <span class="token string">'Go to game start'</span><span class="token punctuation">;</span>
    139. 

  139.       <span class="token keyword">return</span> <span class="token punctuation">(</span>
    140. 

  140.         <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>li</span> <span class="token attr-name">key</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span>move<span class="token punctuation">}</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    141. 

  141.           </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>button</span> <span class="token attr-name">onClick</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">jumpTo</span><span class="token punctuation">(</span>move<span class="token punctuation">)</span><span class="token punctuation">}</span></span><span class="token punctuation">&gt;</span></span><span class="token punctuation">{</span>desc<span class="token punctuation">}</span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>button</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    142. 

  142.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>li</span><span class="token punctuation">&gt;</span></span>
    143. 

  143.       <span class="token punctuation">)</span>
    144. 

  144.     <span class="token punctuation">}</span><span class="token punctuation">)</span>
    145. 

  145. 

  146.     <span class="token keyword">let</span> status
    147. 

  147.     <span class="token keyword">if</span> <span class="token punctuation">(</span>winner<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    148. 

  148.       status <span class="token operator">=</span> <span class="token string">'获胜者: '</span> <span class="token operator">+</span> winner<span class="token punctuation">;</span>
    149. 

  149.     <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    150. 

  150.       status <span class="token operator">=</span> <span class="token string">'下一步玩家: '</span> <span class="token operator">+</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span>state<span class="token punctuation">.</span>xIsNext <span class="token operator">?</span> <span class="token string">'X'</span> <span class="token operator">:</span> <span class="token string">'O'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    151. 

  151.     <span class="token punctuation">}</span>
    152. 

  152. 

  153.     <span class="token comment">// 注意：这里的onClick是传参，而不是直接绑定点击事件</span>
    154. 

  154.     <span class="token keyword">return</span> <span class="token punctuation">(</span>
    155. 

  155.       <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>game<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    156. 

  156.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>game-board<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    157. 

  157.           </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span><span class="token class-name">Board</span></span>
    158. 

  158.             <span class="token attr-name">squares</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span>current<span class="token punctuation">.</span>squares<span class="token punctuation">}</span></span>
    159. 

  159.             <span class="token attr-name">onClick</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span><span class="token punctuation">(</span><span class="token parameter">i</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">handleClick</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">}</span></span>
    160. 

  160.           <span class="token punctuation">/&gt;</span></span><span class="token plain-text">
    161. 

  161.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    162. 

  162.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>game-info<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    163. 

  163.           </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">{</span>status<span class="token punctuation">}</span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    164. 

  164.           </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>ol</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">{</span>moves<span class="token punctuation">}</span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>ol</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    165. 

  165.         </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    166. 

  166.       </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
    167. 

  167.     <span class="token punctuation">)</span>
    168. 

  168.   <span class="token punctuation">}</span>
    169. 

  169. <span class="token punctuation">}</span>
    170. 

  170. 

  171. ReactDOM<span class="token punctuation">.</span><span class="token function">render</span><span class="token punctuation">(</span>
    172. 

  172.   <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span><span class="token class-name">Game</span></span> <span class="token punctuation">/&gt;</span></span><span class="token punctuation">,</span>
    173. 

  173.   document<span class="token punctuation">.</span><span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token string">'root'</span><span class="token punctuation">)</span>
    174. 

  174. <span class="token punctuation">)</span>
    175. 

  175. 

  176. <span class="token comment">// 计算获胜者</span>
    177. 

  177. <span class="token keyword">function</span> <span class="token function">calculateWinner</span> <span class="token punctuation">(</span><span class="token parameter">squares</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    178. 

  178.   <span class="token comment">// 获胜条件的排列方式</span>
    179. 

  179.   <span class="token keyword">const</span> lines <span class="token operator">=</span> <span class="token punctuation">[</span>
    180. 

  180.     <span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
    181. 

  181.     <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
    182. 

  182.     <span class="token punctuation">[</span><span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">7</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
    183. 

  183.     <span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
    184. 

  184.     <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">7</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
    185. 

  185.     <span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
    186. 

  186.     <span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
    187. 

  187.     <span class="token punctuation">[</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
    188. 

  188.   <span class="token punctuation">]</span><span class="token punctuation">;</span>
    189. 

  189. 

  190.   <span class="token comment">// 判断某个排列方式中的值是相同的即获胜，并返回获胜者</span>
    191. 

  191.   <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> lines<span class="token punctuation">.</span>length<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    192. 

  192.     <span class="token keyword">const</span> <span class="token punctuation">[</span>a<span class="token punctuation">,</span> b<span class="token punctuation">,</span> c<span class="token punctuation">]</span> <span class="token operator">=</span> lines<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
    193. 

  193.     <span class="token keyword">if</span> <span class="token punctuation">(</span>squares<span class="token punctuation">[</span>a<span class="token punctuation">]</span> <span class="token operator">&amp;&amp;</span> squares<span class="token punctuation">[</span>a<span class="token punctuation">]</span> <span class="token operator">===</span> squares<span class="token punctuation">[</span>b<span class="token punctuation">]</span> <span class="token operator">&amp;&amp;</span> squares<span class="token punctuation">[</span>a<span class="token punctuation">]</span> <span class="token operator">===</span> squares<span class="token punctuation">[</span>c<span class="token punctuation">]</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    194. 

  194.       <span class="token keyword">return</span> squares<span class="token punctuation">[</span>a<span class="token punctuation">]</span><span class="token punctuation">;</span>
    195. 

  195.     <span class="token punctuation">}</span>
    196. 

  196.   <span class="token punctuation">}</span>
    197. 

  197.   <span class="token keyword">return</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
    198. 

  198. <span class="token punctuation">}</span>
    199. 

  199. 

  200. </code></pre> <div class="line-numbers-wrapper"><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><span 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class="line-number">150</span><br><span class="line-number">151</span><br><span class="line-number">152</span><br><span class="line-number">153</span><br><span class="line-number">154</span><br><span class="line-number">155</span><br><span class="line-number">156</span><br><span class="line-number">157</span><br><span class="line-number">158</span><br><span class="line-number">159</span><br><span class="line-number">160</span><br><span class="line-number">161</span><br><span class="line-number">162</span><br><span class="line-number">163</span><br><span class="line-number">164</span><br><span class="line-number">165</span><br><span class="line-number">166</span><br><span class="line-number">167</span><br><span class="line-number">168</span><br><span class="line-number">169</span><br><span class="line-number">170</span><br><span class="line-number">171</span><br><span class="line-number">172</span><br><span class="line-number">173</span><br><span class="line-number">174</span><br><span class="line-number">175</span><br></div></div><h2 id="为什么不可变性在-react-中非常重要"><a href="#为什么不可变性在-react-中非常重要" class="header-anchor">#</a> 为什么不可变性在 React 中非常重要</h2> <p>案例中，在修改<code>state</code>时并非直接修改对象属性内的某个直，而是先使用<code>.slice()</code> 方法创建了数组的一个副本。然后在通过<code>setState()</code>方法，替换掉整个数组。</p> <p>一般来说，有两种改变数据的方式。第一种方式是直接<em>修改</em>变量的值，第二种方式是使用新的一份数据替换旧数据。</p> <h3 id="直接修改数据"><a href="#直接修改数据" class="header-anchor">#</a> 直接修改数据</h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> player <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token literal-property property">score</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token literal-property property">name</span><span class="token operator">:</span> <span class="token string">'Jeff'</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
    201. 

  201. player<span class="token punctuation">.</span>score <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
    202. 

  202. <span class="token comment">// player 修改后的值为 {score: 2, name: 'Jeff'}</span>
    203. 

  203. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><h3 id="新数据替换旧数据"><a href="#新数据替换旧数据" class="header-anchor">#</a> 新数据替换旧数据</h3> <div class="language-js line-numbers-mode"><pre class="language-js"><code><span class="token keyword">var</span> player <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token literal-property property">score</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token literal-property property">name</span><span class="token operator">:</span> <span class="token string">'Jeff'</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
    204. 

  204. 

  205. <span class="token keyword">var</span> newPlayer <span class="token operator">=</span> Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">,</span> player<span class="token punctuation">,</span> <span class="token punctuation">{</span><span class="token literal-property property">score</span><span class="token operator">:</span> <span class="token number">2</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    206. 

  206. <span class="token comment">// player 的值没有改变, 但是 newPlayer 的值是 {score: 2, name: 'Jeff'}</span>
    207. 

  207. 

  208. <span class="token comment">// 使用对象展开语法，就可以写成：</span>
    209. 

  209. <span class="token comment">// var newPlayer = {...player, score: 2};</span>
    210. 

  210. </code></pre> <div class="line-numbers-wrapper"><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>不直接修改（或改变底层数据）这种方式和前一种方式的结果是一样的，这种方式有以下几点好处：</p> <h3 id="简化复杂的功能"><a href="#简化复杂的功能" class="header-anchor">#</a> 简化复杂的功能</h3> <p><strong>不可变性使得复杂的特性更容易实现</strong>。在后面的章节里，我们会实现一种叫做“时间旅行”的功能。“时间旅行”可以使我们回顾井字棋的历史步骤，并且可以“跳回”之前的步骤。这个功能并不是只有游戏才会用到——撤销和恢复功能在开发中是一个很常见的需求。<strong>不直接在数据上修改可以让我们追溯并复用游戏的历史记录</strong>。</p> <h3 id="跟踪数据的改变"><a href="#跟踪数据的改变" class="header-anchor">#</a> 跟踪数据的改变</h3> <p>如果直接修改数据，那么就很难跟踪到数据的改变。跟踪数据的改变需要可变对象可以与改变之前的版本进行对比，这样整个对象树都需要被遍历一次。</p> <p>**跟踪不可变数据的变化相对来说就容易多了。**如果发现对象变成了一个新对象，那么我们就可以说对象发生改变了。</p> <h4 id=""><a href="#" class="header-anchor">#</a></h4> <h3 id="确定在-react-中何时重新渲染"><a href="#确定在-react-中何时重新渲染" class="header-anchor">#</a> 确定在 React 中何时重新渲染</h3> <p>不可变性最主要的优势在于它可以帮助我们在 React 中创建 <em>pure components</em>。我们可以很轻松的确定不可变数据是否发生了改变，从而确定何时对组件进行重新渲染。</p> <p>查阅<a href="https://zh-hans.reactjs.org/docs/optimizing-performance.html#examples" target="_blank" rel="noopener noreferrer">性能优化<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a>章节，以了解更多有关 <code>shouldComponentUpdate()</code> 函数及如何构建 <em>pure components</em> 的内容。</p> <h3 id="-2"><a href="#-2" class="header-anchor">#</a></h3></div></div>  <div class="page-edit"><div class="edit-link"><a href="https://github.com/heBody/blog/edit/master/docs/《React》笔记/04.案例演示/01.案例演示.md" target="_blank" rel="noopener noreferrer">编辑</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <div class="tags"><a href="/blog/tags/?tag=React" title="标签">#React</a></div> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2022/12/14, 19:36:42</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/blog/pages/cf1018/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">自定义 Hook</div></a> <!----></div> <div class="page-nav"><p class="inner"><span class="prev">
    211. 

  211.         ←
    212. 

  212.         <a href="/blog/pages/cf1018/" class="prev">自定义 Hook</a></span> <!----></p></div></div></div> <div class="article-list"><div class="article-title"><a href="/blog/archives/" class="iconfont icon-bi">最近更新</a></div> <div class="article-wrapper"><dl><dd>01</dd> <dt><a href="/blog/pages/922650/"><div>
    213. 

  213.             Git修改分支名
    214. 

  214.             <!----></div></a> <span class="date">08-11</span></dt></dl><dl><dd>02</dd> <dt><a href="/blog/pages/55f894/"><div>
    215. 

  215.             CSS给table的tbody添加滚动条
    216. 

  216.             <!----></div></a> <span class="date">06-29</span></dt></dl><dl><dd>03</dd> <dt><a href="/blog/pages/829589/"><div>
    217. 

  217.             我做了一个手写春联小网页，祝大家虎年暴富
    218. 

  218.             <span class="title-tag">
    219. 

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