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class="sidebar-link">最新提案</a></li><li><a href="/blog/pages/e97bc1e5626b082c/" aria-current="page" class="active sidebar-link">装饰器</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level2"><a href="/blog/pages/e97bc1e5626b082c/#类的装饰" class="sidebar-link">类的装饰</a></li><li class="sidebar-sub-header level2"><a href="/blog/pages/e97bc1e5626b082c/#方法的装饰" class="sidebar-link">方法的装饰</a></li><li class="sidebar-sub-header level2"><a href="/blog/pages/e97bc1e5626b082c/#为什么装饰器不能用于函数" class="sidebar-link">为什么装饰器不能用于函数？</a></li><li class="sidebar-sub-header level2"><a href="/blog/pages/e97bc1e5626b082c/#core-decorators-js" class="sidebar-link">core-decorators.js</a></li><li class="sidebar-sub-header level2"><a href="/blog/pages/e97bc1e5626b082c/#使用装饰器实现自动发布事件" class="sidebar-link">使用装饰器实现自动发布事件</a></li><li class="sidebar-sub-header level2"><a href="/blog/pages/e97bc1e5626b082c/#mixin" class="sidebar-link">Mixin</a></li><li class="sidebar-sub-header level2"><a href="/blog/pages/e97bc1e5626b082c/#trait" class="sidebar-link">Trait</a></li></ul></li><li><a href="/blog/pages/1cf50330655efc69/" class="sidebar-link">函数式编程</a></li><li><a href="/blog/pages/6a8e2dc558da1b39/" class="sidebar-link">Mixin</a></li><li><a href="/blog/pages/8e8f80f69b775a56/" class="sidebar-link">SIMD</a></li><li><a href="/blog/pages/ea6f3b870f6dab69/" class="sidebar-link">参考链接</a></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/es6/#《ES6 教程》笔记" data-v-06970110>《ES6 教程》笔记</a></li></ul> <div class="info" data-v-06970110><div title="作者" class="author iconfont icon-touxiang" data-v-06970110><a href="javascript:;" data-v-06970110>阮一峰</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-06970110><a href="javascript:;" data-v-06970110>2020-02-09</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,iVBORw0KGgoAAAANSUhEUgAAAB4AAAAeCAYAAAA7MK6iAAAAAXNSR0IArs4c6QAABH1JREFUSA3tVl1oHFUUPmdmd2ltklqbpJDiNnXFmgbFktho7YMPNiJSSZM0+CAYSkUELVhM6YuwIPpgoOKDqOBDC0XE2CQoNtQXBUFTTcCi+Wlh1V2TQExsUzcltd3M9Tt3ZjZzZ2fT+OJTL8yeM+eee757fmeJbq//KQL8X3DUSFOcfr7cRsRtxNQMWueeVzOkaITIGqQHNg5y8+jNW9ldM7A6nTpAjuolUikAwq7CE3WcM2RRDz+XGVgN3FptU/aUSlvq9Pa3iZ1+sgAqJyyAFqkipd9dqiwHF3P65YycLWc/6sqGrvoEoIp6DOFaX5h6+dnfjkWprwqsPk0dUGq5vySwDImC10KxFHgGL1SWoc92O3eVht09qdXNH11I2SsTsJYqMWzihqGMi+A+Garf3BAuuLI5oGlULyNfyB/HYNujwktOfRrMr5t77NmevqaUopx0grnKAyvVpmwUDB4x6FPXuGvYLTDwWsejwgtgkYKPqRJg8SV6xaiZ3ZTppGneS4yfH5/66fZSDHv+QZci/+h5c5UHtpy67JUqGppM0sh0Nc1dW6/N1W5Yoqat8/TU/VnadmdeW2PLLSyh0cvxBs3KbqTmwYPpxN4do/mzE8nEpvX/UMu2Wbp74zUAK5q6WkHns7V0eWkdPbPzd3rxkTGybadYySumVzhcaJFbs5UrEkQ/+CK8gF5dnh/6ciIZ73gwQ927L1IitoxKLXYP3SjYdOrHHfTZhRRlFyrorafPk20B3HPD1y2G3qKZME5Jcf3t/HUC13/8tSd++vqFveMUTwAUxSUFI1QekR1+bIze3D9MF2aq6cPvG72CgnldWCFqyRw3lwH8ZMerjTD9ElRO7Gv44wNpC90aASqGfVlz/Rx17srQ57/UU26hkhQqUB7dBR71WmzQhHUnblGmVOEw0jhbV1n9OlXUDCIRGaNV5Jp43N516fN7JmnTHdfp7Hgy0luO4aMhtkLL8Bi3bUWYvzh5Mn1dTxrL6QmGuRhGL/TiTTxRoEdTszSaq9GR0NGA3KdkOz3hqSV3MIDhQ5IVX/Ivx3umBti2es2h4eZby7x8br1rkf7Mo90AqC8aQ3sJeNzqFRu+vSANAQe3PL7l0HGOAdwDCeZYvNKeoZp1Qfs6Aipndh86HmFRi0LAnEO47wsqM6cdfjh3jBPUzhZy7nvlUfFsamED1VQt6aISHVymXZ/B2aCtIG8AI8xfobj2d3en1wWVhOeHELKmLQ1s211s88comkv4UCwWyF787mJdYXtNfhKAXVqnKTq8QZvGAGGOfaTo5pGZ/PwbUCr5+DPr/1J92JNHr9aOl/F3iI5+O1nfybsGxoimvZ3ViWSluDITw3P37mypheDIPY0tw7+O/5ApbkYw+zpfaUVu32Pi98+defdUhEpZkRFq0aqyNh9FuL9hpYbEm6iwi0z2REd09ZmyENEbuhjDWzKvZXTqKYaBIr3tt5kuPtQBZFvEUwHt60vfCNu41XsksH9Ij1BMMz1Y0OOunHNShFIP5868g5zeXmuLwL9T4b6Q2+KejgAAAABJRU5ErkJggg==">装饰器<!----></h1>  <div class="theme-vdoing-content content__default"><h1 id="装饰器"><a href="#装饰器" class="header-anchor">#</a> 装饰器</h1> <p>[说明] Decorator 提案经过了大幅修改，目前还没有定案，不知道语法会不会再变。下面的内容完全依据以前的提案，已经有点过时了。等待定案以后，需要完全重写。</p> <p>装饰器（Decorator）是一种与类（class）相关的语法，用来注释或修改类和类方法。许多面向对象的语言都有这项功能，目前有一个<a href="https://github.com/tc39/proposal-decorators" target="_blank" rel="noopener noreferrer">提案<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>将其引入了 ECMAScript。
    26. 

  26. 

  27. 装饰器是一种函数，写成<code>@ + 函数名</code>。它可以放在类和类方法的定义前面。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>@frozen <span class="token keyword">class</span> <span class="token class-name">Foo</span> <span class="token punctuation">{</span>
    28. 

  28.   @<span class="token function">configurable</span><span class="token punctuation">(</span><span class="token boolean">false</span><span class="token punctuation">)</span>
    29. 

  29.   @<span class="token function">enumerable</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span>
    30. 

  30.   <span class="token function">method</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    31. 

  31. 

  32.   @<span class="token function">throttle</span><span class="token punctuation">(</span><span class="token number">500</span><span class="token punctuation">)</span>
    33. 

  33.   <span class="token function">expensiveMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    34. 

  34. <span class="token punctuation">}</span>
    35. 

  35. </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></div></div><p>上面代码一共使用了四个装饰器，一个用在类本身，另外三个用在类方法。它们不仅增加了代码的可读性，清晰地表达了意图，而且提供一种方便的手段，增加或修改类的功能。</p> <h2 id="类的装饰"><a href="#类的装饰" class="header-anchor">#</a> 类的装饰</h2> <p>装饰器可以用来装饰整个类。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>@testable
    36. 

  36. <span class="token keyword">class</span> <span class="token class-name">MyTestableClass</span> <span class="token punctuation">{</span>
    37. 

  37.   <span class="token comment">// ...</span>
    38. 

  38. <span class="token punctuation">}</span>
    39. 

  39. 

  40. <span class="token keyword">function</span> <span class="token function">testable</span><span class="token punctuation">(</span><span class="token parameter">target</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    41. 

  41.   target<span class="token punctuation">.</span>isTestable <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
    42. 

  42. <span class="token punctuation">}</span>
    43. 

  43. 

  44. MyTestableClass<span class="token punctuation">.</span>isTestable <span class="token comment">// true</span>
    45. 

  45. </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></div></div><p>上面代码中，<code>@testable</code>就是一个装饰器。它修改了<code>MyTestableClass</code>这个类的行为，为它加上了静态属性<code>isTestable</code>。<code>testable</code>函数的参数<code>target</code>是<code>MyTestableClass</code>类本身。</p> <p>基本上，装饰器的行为就是下面这样。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>@decorator
    46. 

  46. <span class="token keyword">class</span> <span class="token class-name">A</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    47. 

  47. 

  48. <span class="token comment">// 等同于</span>
    49. 

  49. 

  50. <span class="token keyword">class</span> <span class="token class-name">A</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    51. 

  51. <span class="token constant">A</span> <span class="token operator">=</span> <span class="token function">decorator</span><span class="token punctuation">(</span><span class="token constant">A</span><span class="token punctuation">)</span> <span class="token operator">||</span> <span class="token constant">A</span><span class="token punctuation">;</span>
    52. 

  52. </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>也就是说，装饰器是一个对类进行处理的函数。装饰器函数的第一个参数，就是所要装饰的目标类。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">testable</span><span class="token punctuation">(</span><span class="token parameter">target</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    53. 

  53.   <span class="token comment">// ...</span>
    54. 

  54. <span class="token punctuation">}</span>
    55. 

  55. </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><p>上面代码中，<code>testable</code>函数的参数<code>target</code>，就是会被装饰的类。</p> <p>如果觉得一个参数不够用，可以在装饰器外面再封装一层函数。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">testable</span><span class="token punctuation">(</span><span class="token parameter">isTestable</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    56. 

  56.   <span class="token keyword">return</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">target</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    57. 

  57.     target<span class="token punctuation">.</span>isTestable <span class="token operator">=</span> isTestable<span class="token punctuation">;</span>
    58. 

  58.   <span class="token punctuation">}</span>
    59. 

  59. <span class="token punctuation">}</span>
    60. 

  60. 

  61. @<span class="token function">testable</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span>
    62. 

  62. <span class="token keyword">class</span> <span class="token class-name">MyTestableClass</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    63. 

  63. MyTestableClass<span class="token punctuation">.</span>isTestable <span class="token comment">// true</span>
    64. 

  64. 

  65. @<span class="token function">testable</span><span class="token punctuation">(</span><span class="token boolean">false</span><span class="token punctuation">)</span>
    66. 

  66. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    67. 

  67. MyClass<span class="token punctuation">.</span>isTestable <span class="token comment">// false</span>
    68. 

  68. </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></div></div><p>上面代码中，装饰器<code>testable</code>可以接受参数，这就等于可以修改装饰器的行为。</p> <p>注意，装饰器对类的行为的改变，是代码编译时发生的，而不是在运行时。这意味着，装饰器能在编译阶段运行代码。也就是说，装饰器本质就是编译时执行的函数。</p> <p>前面的例子是为类添加一个静态属性，如果想添加实例属性，可以通过目标类的<code>prototype</code>对象操作。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">testable</span><span class="token punctuation">(</span><span class="token parameter">target</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    69. 

  69.   target<span class="token punctuation">.</span>prototype<span class="token punctuation">.</span>isTestable <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
    70. 

  70. <span class="token punctuation">}</span>
    71. 

  71. 

  72. @testable
    73. 

  73. <span class="token keyword">class</span> <span class="token class-name">MyTestableClass</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    74. 

  74. 

  75. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyTestableClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    76. 

  76. obj<span class="token punctuation">.</span>isTestable <span class="token comment">// true</span>
    77. 

  77. </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></div></div><p>上面代码中，装饰器函数<code>testable</code>是在目标类的<code>prototype</code>对象上添加属性，因此就可以在实例上调用。</p> <p>下面是另外一个例子。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// mixins.js</span>
    78. 

  78. <span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">mixins</span><span class="token punctuation">(</span><span class="token parameter"><span class="token operator">...</span>list</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    79. 

  79.   <span class="token keyword">return</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">target</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    80. 

  80.     Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span>target<span class="token punctuation">.</span>prototype<span class="token punctuation">,</span> <span class="token operator">...</span>list<span class="token punctuation">)</span>
    81. 

  81.   <span class="token punctuation">}</span>
    82. 

  82. <span class="token punctuation">}</span>
    83. 

  83. 

  84. <span class="token comment">// main.js</span>
    85. 

  85. <span class="token keyword">import</span> <span class="token punctuation">{</span> mixins <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'./mixins'</span>
    86. 

  86. 

  87. <span class="token keyword">const</span> Foo <span class="token operator">=</span> <span class="token punctuation">{</span>
    88. 

  88.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    89. 

  89. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    90. 

  90. 

  91. @<span class="token function">mixins</span><span class="token punctuation">(</span>Foo<span class="token punctuation">)</span>
    92. 

  92. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    93. 

  93. 

  94. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    95. 

  95. obj<span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 'foo'</span>
    96. 

  96. </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></div></div><p>上面代码通过装饰器<code>mixins</code>，把<code>Foo</code>对象的方法添加到了<code>MyClass</code>的实例上面。可以用<code>Object.assign()</code>模拟这个功能。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> Foo <span class="token operator">=</span> <span class="token punctuation">{</span>
    97. 

  97.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    98. 

  98. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    99. 

  99. 

  100. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    101. 

  101. 

  102. Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token class-name">MyClass</span><span class="token punctuation">.</span>prototype<span class="token punctuation">,</span> Foo<span class="token punctuation">)</span><span class="token punctuation">;</span>
    103. 

  103. 

  104. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    105. 

  105. obj<span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 'foo'</span>
    106. 

  106. </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></div></div><p>实际开发中，React 与 Redux 库结合使用时，常常需要写成下面这样。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">class</span> <span class="token class-name">MyReactComponent</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><span class="token punctuation">}</span>
    107. 

  107. 

  108. <span class="token keyword">export</span> <span class="token keyword">default</span> <span class="token function">connect</span><span class="token punctuation">(</span>mapStateToProps<span class="token punctuation">,</span> mapDispatchToProps<span class="token punctuation">)</span><span class="token punctuation">(</span>MyReactComponent<span class="token punctuation">)</span><span class="token punctuation">;</span>
    109. 

  109. </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><p>有了装饰器，就可以改写上面的代码。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>@<span class="token function">connect</span><span class="token punctuation">(</span>mapStateToProps<span class="token punctuation">,</span> mapDispatchToProps<span class="token punctuation">)</span>
    110. 

  110. <span class="token keyword">export</span> <span class="token keyword">default</span> <span class="token keyword">class</span> <span class="token class-name">MyReactComponent</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><span class="token punctuation">}</span>
    111. 

  111. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>相对来说，后一种写法看上去更容易理解。</p> <h2 id="方法的装饰"><a href="#方法的装饰" class="header-anchor">#</a> 方法的装饰</h2> <p>装饰器不仅可以装饰类，还可以装饰类的属性。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">class</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
    112. 

  112.   @readonly
    113. 

  113.   <span class="token function">name</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span><span class="token keyword">this</span><span class="token punctuation">.</span>first<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span><span class="token keyword">this</span><span class="token punctuation">.</span>last<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span> <span class="token punctuation">}</span>
    114. 

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

  115. </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></div></div><p>上面代码中，装饰器<code>readonly</code>用来装饰“类”的<code>name</code>方法。</p> <p>装饰器函数<code>readonly</code>一共可以接受三个参数。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">readonly</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> name<span class="token punctuation">,</span> descriptor</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    116. 

  116.   <span class="token comment">// descriptor对象原来的值如下</span>
    117. 

  117.   <span class="token comment">// {</span>
    118. 

  118.   <span class="token comment">//   value: specifiedFunction,</span>
    119. 

  119.   <span class="token comment">//   enumerable: false,</span>
    120. 

  120.   <span class="token comment">//   configurable: true,</span>
    121. 

  121.   <span class="token comment">//   writable: true</span>
    122. 

  122.   <span class="token comment">// };</span>
    123. 

  123.   descriptor<span class="token punctuation">.</span>writable <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
    124. 

  124.   <span class="token keyword">return</span> descriptor<span class="token punctuation">;</span>
    125. 

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

  126. 

  127. <span class="token function">readonly</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token punctuation">.</span>prototype<span class="token punctuation">,</span> <span class="token string">'name'</span><span class="token punctuation">,</span> descriptor<span class="token punctuation">)</span><span class="token punctuation">;</span>
    128. 

  128. <span class="token comment">// 类似于</span>
    129. 

  129. Object<span class="token punctuation">.</span><span class="token function">defineProperty</span><span class="token punctuation">(</span><span class="token class-name">Person</span><span class="token punctuation">.</span>prototype<span class="token punctuation">,</span> <span class="token string">'name'</span><span class="token punctuation">,</span> descriptor<span class="token punctuation">)</span><span class="token punctuation">;</span>
    130. 

  130. </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></div></div><p>装饰器第一个参数是类的原型对象，上例是<code>Person.prototype</code>，装饰器的本意是要“装饰”类的实例，但是这个时候实例还没生成，所以只能去装饰原型（这不同于类的装饰，那种情况时<code>target</code>参数指的是类本身）；第二个参数是所要装饰的属性名，第三个参数是该属性的描述对象。</p> <p>另外，上面代码说明，装饰器（readonly）会修改属性的描述对象（descriptor），然后被修改的描述对象再用来定义属性。</p> <p>下面是另一个例子，修改属性描述对象的<code>enumerable</code>属性，使得该属性不可遍历。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">class</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
    131. 

  131.   @nonenumerable
    132. 

  132.   <span class="token keyword">get</span> <span class="token function">kidCount</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>children<span class="token punctuation">.</span>length<span class="token punctuation">;</span> <span class="token punctuation">}</span>
    133. 

  133. <span class="token punctuation">}</span>
    134. 

  134. 

  135. <span class="token keyword">function</span> <span class="token function">nonenumerable</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> name<span class="token punctuation">,</span> descriptor</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    136. 

  136.   descriptor<span class="token punctuation">.</span>enumerable <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
    137. 

  137.   <span class="token keyword">return</span> descriptor<span class="token punctuation">;</span>
    138. 

  138. <span class="token punctuation">}</span>
    139. 

  139. </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></div></div><p>下面的<code>@log</code>装饰器，可以起到输出日志的作用。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">class</span> <span class="token class-name">Math</span> <span class="token punctuation">{</span>
    140. 

  140.   @log
    141. 

  141.   <span class="token function">add</span><span class="token punctuation">(</span><span class="token parameter">a<span class="token punctuation">,</span> b</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    142. 

  142.     <span class="token keyword">return</span> a <span class="token operator">+</span> b<span class="token punctuation">;</span>
    143. 

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

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

  145. 

  146. <span class="token keyword">function</span> <span class="token function">log</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> name<span class="token punctuation">,</span> descriptor</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    147. 

  147.   <span class="token keyword">var</span> oldValue <span class="token operator">=</span> descriptor<span class="token punctuation">.</span>value<span class="token punctuation">;</span>
    148. 

  148. 

  149.   descriptor<span class="token punctuation">.</span><span class="token function-variable function">value</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    150. 

  150.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">Calling </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>name<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> with</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">,</span> arguments<span class="token punctuation">)</span><span class="token punctuation">;</span>
    151. 

  151.     <span class="token keyword">return</span> <span class="token function">oldValue</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">,</span> arguments<span class="token punctuation">)</span><span class="token punctuation">;</span>
    152. 

  152.   <span class="token punctuation">}</span><span class="token punctuation">;</span>
    153. 

  153. 

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

  155. <span class="token punctuation">}</span>
    156. 

  156. 

  157. <span class="token keyword">const</span> math <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Math</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    158. 

  158. 

  159. <span class="token comment">// passed parameters should get logged now</span>
    160. 

  160. math<span class="token punctuation">.</span><span class="token function">add</span><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 punctuation">;</span>
    161. 

  161. </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></div></div><p>上面代码中，<code>@log</code>装饰器的作用就是在执行原始的操作之前，执行一次<code>console.log</code>，从而达到输出日志的目的。</p> <p>装饰器有注释的作用。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>@testable
    162. 

  162. <span class="token keyword">class</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
    163. 

  163.   @readonly
    164. 

  164.   @nonenumerable
    165. 

  165.   <span class="token function">name</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span><span class="token keyword">this</span><span class="token punctuation">.</span>first<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span><span class="token keyword">this</span><span class="token punctuation">.</span>last<span class="token interpolation-punctuation punctuation">}</span></span><span class="token template-punctuation string">`</span></span> <span class="token punctuation">}</span>
    166. 

  166. <span class="token punctuation">}</span>
    167. 

  167. </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></div></div><p>从上面代码中，我们一眼就能看出，<code>Person</code>类是可测试的，而<code>name</code>方法是只读和不可枚举的。</p> <p>下面是使用 Decorator 写法的<a href="https://github.com/ionic-team/stencil" target="_blank" rel="noopener noreferrer">组件<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>，看上去一目了然。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>@<span class="token function">Component</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    168. 

  168.   <span class="token literal-property property">tag</span><span class="token operator">:</span> <span class="token string">'my-component'</span><span class="token punctuation">,</span>
    169. 

  169.   <span class="token literal-property property">styleUrl</span><span class="token operator">:</span> <span class="token string">'my-component.scss'</span>
    170. 

  170. <span class="token punctuation">}</span><span class="token punctuation">)</span>
    171. 

  171. <span class="token keyword">export</span> <span class="token keyword">class</span> <span class="token class-name">MyComponent</span> <span class="token punctuation">{</span>
    172. 

  172.   @<span class="token function">Prop</span><span class="token punctuation">(</span><span class="token punctuation">)</span> first<span class="token operator">:</span> string<span class="token punctuation">;</span>
    173. 

  173.   @<span class="token function">Prop</span><span class="token punctuation">(</span><span class="token punctuation">)</span> last<span class="token operator">:</span> string<span class="token punctuation">;</span>
    174. 

  174.   @<span class="token function">State</span><span class="token punctuation">(</span><span class="token punctuation">)</span> isVisible<span class="token operator">:</span> boolean <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
    175. 

  175. 

  176.   <span class="token function">render</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    177. 

  177.     <span class="token keyword">return</span> <span class="token punctuation">(</span>
    178. 

  178.       <span class="token operator">&lt;</span>p<span class="token operator">&gt;</span>Hello<span class="token punctuation">,</span> my name is <span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span>first<span class="token punctuation">}</span> <span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span>last<span class="token punctuation">}</span><span class="token operator">&lt;</span><span class="token operator">/</span>p<span class="token operator">&gt;</span>
    179. 

  179.     <span class="token punctuation">)</span><span class="token punctuation">;</span>
    180. 

  180.   <span class="token punctuation">}</span>
    181. 

  181. <span class="token punctuation">}</span>
    182. 

  182. </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></div></div><p>如果同一个方法有多个装饰器，会像剥洋葱一样，先从外到内进入，然后由内向外执行。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">dec</span><span class="token punctuation">(</span><span class="token parameter">id</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
    183. 

  183.   console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'evaluated'</span><span class="token punctuation">,</span> id<span class="token punctuation">)</span><span class="token punctuation">;</span>
    184. 

  184.   <span class="token keyword">return</span> <span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> property<span class="token punctuation">,</span> descriptor</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'executed'</span><span class="token punctuation">,</span> id<span class="token punctuation">)</span><span class="token punctuation">;</span>
    185. 

  185. <span class="token punctuation">}</span>
    186. 

  186. 

  187. <span class="token keyword">class</span> <span class="token class-name">Example</span> <span class="token punctuation">{</span>
    188. 

  188.     @<span class="token function">dec</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span>
    189. 

  189.     @<span class="token function">dec</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span>
    190. 

  190.     <span class="token function">method</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token punctuation">}</span>
    191. 

  191. <span class="token punctuation">}</span>
    192. 

  192. <span class="token comment">// evaluated 1</span>
    193. 

  193. <span class="token comment">// evaluated 2</span>
    194. 

  194. <span class="token comment">// executed 2</span>
    195. 

  195. <span class="token comment">// executed 1</span>
    196. 

  196. </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></div></div><p>上面代码中，外层装饰器<code>@dec(1)</code>先进入，但是内层装饰器<code>@dec(2)</code>先执行。</p> <p>除了注释，装饰器还能用来类型检查。所以，对于类来说，这项功能相当有用。从长期来看，它将是 JavaScript 代码静态分析的重要工具。</p> <h2 id="为什么装饰器不能用于函数"><a href="#为什么装饰器不能用于函数" class="header-anchor">#</a> 为什么装饰器不能用于函数？</h2> <p>装饰器只能用于类和类的方法，不能用于函数，因为存在函数提升。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> counter <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
    197. 

  197. 

  198. <span class="token keyword">var</span> <span class="token function-variable function">add</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    199. 

  199.   counter<span class="token operator">++</span><span class="token punctuation">;</span>
    200. 

  200. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    201. 

  201. 

  202. @add
    203. 

  203. <span class="token keyword">function</span> <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    204. 

  204. <span class="token punctuation">}</span>
    205. 

  205. </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></div></div><p>上面的代码，意图是执行后<code>counter</code>等于 1，但是实际上结果是<code>counter</code>等于 0。因为函数提升，使得实际执行的代码是下面这样。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>@add
    206. 

  206. <span class="token keyword">function</span> <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    207. 

  207. <span class="token punctuation">}</span>
    208. 

  208. 

  209. <span class="token keyword">var</span> counter<span class="token punctuation">;</span>
    210. 

  210. <span class="token keyword">var</span> add<span class="token punctuation">;</span>
    211. 

  211. 

  212. counter <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
    213. 

  213. 

  214. <span class="token function-variable function">add</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    215. 

  215.   counter<span class="token operator">++</span><span class="token punctuation">;</span>
    216. 

  216. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    217. 

  217. </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></div></div><p>下面是另一个例子。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> readOnly <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">&quot;some-decorator&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    218. 

  218. 

  219. @readOnly
    220. 

  220. <span class="token keyword">function</span> <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    221. 

  221. <span class="token punctuation">}</span>
    222. 

  222. </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></div></div><p>上面代码也有问题，因为实际执行是下面这样。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> readOnly<span class="token punctuation">;</span>
    223. 

  223. 

  224. @readOnly
    225. 

  225. <span class="token keyword">function</span> <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    226. 

  226. <span class="token punctuation">}</span>
    227. 

  227. 

  228. readOnly <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">&quot;some-decorator&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    229. 

  229. </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>总之，由于存在函数提升，使得装饰器不能用于函数。类是不会提升的，所以就没有这方面的问题。</p> <p>另一方面，如果一定要装饰函数，可以采用高阶函数的形式直接执行。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">doSomething</span><span class="token punctuation">(</span><span class="token parameter">name</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    230. 

  230.   console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'Hello, '</span> <span class="token operator">+</span> name<span class="token punctuation">)</span><span class="token punctuation">;</span>
    231. 

  231. <span class="token punctuation">}</span>
    232. 

  232. 

  233. <span class="token keyword">function</span> <span class="token function">loggingDecorator</span><span class="token punctuation">(</span><span class="token parameter">wrapped</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    234. 

  234.   <span class="token keyword">return</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    235. 

  235.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'Starting'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    236. 

  236.     <span class="token keyword">const</span> result <span class="token operator">=</span> <span class="token function">wrapped</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">,</span> arguments<span class="token punctuation">)</span><span class="token punctuation">;</span>
    237. 

  237.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'Finished'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    238. 

  238.     <span class="token keyword">return</span> result<span class="token punctuation">;</span>
    239. 

  239.   <span class="token punctuation">}</span>
    240. 

  240. <span class="token punctuation">}</span>
    241. 

  241. 

  242. <span class="token keyword">const</span> wrapped <span class="token operator">=</span> <span class="token function">loggingDecorator</span><span class="token punctuation">(</span>doSomething<span class="token punctuation">)</span><span class="token punctuation">;</span>
    243. 

  243. </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></div></div><h2 id="core-decorators-js"><a href="#core-decorators-js" class="header-anchor">#</a> core-decorators.js</h2> <p><a href="https://github.com/jayphelps/core-decorators.js" target="_blank" rel="noopener noreferrer">core-decorators.js<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>是一个第三方模块，提供了几个常见的装饰器，通过它可以更好地理解装饰器。</p> <p><strong>（1）@autobind</strong></p> <p><code>autobind</code>装饰器使得方法中的<code>this</code>对象，绑定原始对象。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> autobind <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'core-decorators'</span><span class="token punctuation">;</span>
    244. 

  244. 

  245. <span class="token keyword">class</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
    246. 

  246.   @autobind
    247. 

  247.   <span class="token function">getPerson</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    248. 

  248.     <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">;</span>
    249. 

  249.   <span class="token punctuation">}</span>
    250. 

  250. <span class="token punctuation">}</span>
    251. 

  251. 

  252. <span class="token keyword">let</span> person <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    253. 

  253. <span class="token keyword">let</span> getPerson <span class="token operator">=</span> person<span class="token punctuation">.</span>getPerson<span class="token punctuation">;</span>
    254. 

  254. 

  255. <span class="token function">getPerson</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">===</span> person<span class="token punctuation">;</span>
    256. 

  256. <span class="token comment">// true</span>
    257. 

  257. </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></div></div><p><strong>（2）@readonly</strong></p> <p><code>readonly</code>装饰器使得属性或方法不可写。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> readonly <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'core-decorators'</span><span class="token punctuation">;</span>
    258. 

  258. 

  259. <span class="token keyword">class</span> <span class="token class-name">Meal</span> <span class="token punctuation">{</span>
    260. 

  260.   @readonly
    261. 

  261.   entree <span class="token operator">=</span> <span class="token string">'steak'</span><span class="token punctuation">;</span>
    262. 

  262. <span class="token punctuation">}</span>
    263. 

  263. 

  264. <span class="token keyword">var</span> dinner <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Meal</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    265. 

  265. dinner<span class="token punctuation">.</span>entree <span class="token operator">=</span> <span class="token string">'salmon'</span><span class="token punctuation">;</span>
    266. 

  266. <span class="token comment">// Cannot assign to read only property 'entree' of [object Object]</span>
    267. 

  267. </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></div></div><p><strong>（3）@override</strong></p> <p><code>override</code>装饰器检查子类的方法，是否正确覆盖了父类的同名方法，如果不正确会报错。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> override <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'core-decorators'</span><span class="token punctuation">;</span>
    268. 

  268. 

  269. <span class="token keyword">class</span> <span class="token class-name">Parent</span> <span class="token punctuation">{</span>
    270. 

  270.   <span class="token function">speak</span><span class="token punctuation">(</span><span class="token parameter">first<span class="token punctuation">,</span> second</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    271. 

  271. <span class="token punctuation">}</span>
    272. 

  272. 

  273. <span class="token keyword">class</span> <span class="token class-name">Child</span> <span class="token keyword">extends</span> <span class="token class-name">Parent</span> <span class="token punctuation">{</span>
    274. 

  274.   @override
    275. 

  275.   <span class="token function">speak</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    276. 

  276.   <span class="token comment">// SyntaxError: Child#speak() does not properly override Parent#speak(first, second)</span>
    277. 

  277. <span class="token punctuation">}</span>
    278. 

  278. 

  279. <span class="token comment">// or</span>
    280. 

  280. 

  281. <span class="token keyword">class</span> <span class="token class-name">Child</span> <span class="token keyword">extends</span> <span class="token class-name">Parent</span> <span class="token punctuation">{</span>
    282. 

  282.   @override
    283. 

  283.   <span class="token function">speaks</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    284. 

  284.   <span class="token comment">// SyntaxError: No descriptor matching Child#speaks() was found on the prototype chain.</span>
    285. 

  285.   <span class="token comment">//</span>
    286. 

  286.   <span class="token comment">//   Did you mean &quot;speak&quot;?</span>
    287. 

  287. <span class="token punctuation">}</span>
    288. 

  288. </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></div></div><p><strong>（4）@deprecate (别名@deprecated)</strong></p> <p><code>deprecate</code>或<code>deprecated</code>装饰器在控制台显示一条警告，表示该方法将废除。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> deprecate <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'core-decorators'</span><span class="token punctuation">;</span>
    289. 

  289. 

  290. <span class="token keyword">class</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
    291. 

  291.   @deprecate
    292. 

  292.   <span class="token function">facepalm</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    293. 

  293. 

  294.   @<span class="token function">deprecate</span><span class="token punctuation">(</span><span class="token string">'We stopped facepalming'</span><span class="token punctuation">)</span>
    295. 

  295.   <span class="token function">facepalmHard</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    296. 

  296. 

  297.   @<span class="token function">deprecate</span><span class="token punctuation">(</span><span class="token string">'We stopped facepalming'</span><span class="token punctuation">,</span> <span class="token punctuation">{</span> <span class="token literal-property property">url</span><span class="token operator">:</span> <span class="token string">'http://knowyourmeme.com/memes/facepalm'</span> <span class="token punctuation">}</span><span class="token punctuation">)</span>
    298. 

  298.   <span class="token function">facepalmHarder</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    299. 

  299. <span class="token punctuation">}</span>
    300. 

  300. 

  301. <span class="token keyword">let</span> person <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    302. 

  302. 

  303. person<span class="token punctuation">.</span><span class="token function">facepalm</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    304. 

  304. <span class="token comment">// DEPRECATION Person#facepalm: This function will be removed in future versions.</span>
    305. 

  305. 

  306. person<span class="token punctuation">.</span><span class="token function">facepalmHard</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    307. 

  307. <span class="token comment">// DEPRECATION Person#facepalmHard: We stopped facepalming</span>
    308. 

  308. 

  309. person<span class="token punctuation">.</span><span class="token function">facepalmHarder</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    310. 

  310. <span class="token comment">// DEPRECATION Person#facepalmHarder: We stopped facepalming</span>
    311. 

  311. <span class="token comment">//</span>
    312. 

  312. <span class="token comment">//     See http://knowyourmeme.com/memes/facepalm for more details.</span>
    313. 

  313. <span class="token comment">//</span>
    314. 

  314. </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 class="line-number">25</span><br><span class="line-number">26</span><br></div></div><p><strong>（5）@suppressWarnings</strong></p> <p><code>suppressWarnings</code>装饰器抑制<code>deprecated</code>装饰器导致的<code>console.warn()</code>调用。但是，异步代码发出的调用除外。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> suppressWarnings <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'core-decorators'</span><span class="token punctuation">;</span>
    315. 

  315. 

  316. <span class="token keyword">class</span> <span class="token class-name">Person</span> <span class="token punctuation">{</span>
    317. 

  317.   @deprecated
    318. 

  318.   <span class="token function">facepalm</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    319. 

  319. 

  320.   @suppressWarnings
    321. 

  321.   <span class="token function">facepalmWithoutWarning</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    322. 

  322.     <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">facepalm</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    323. 

  323.   <span class="token punctuation">}</span>
    324. 

  324. <span class="token punctuation">}</span>
    325. 

  325. 

  326. <span class="token keyword">let</span> person <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Person</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    327. 

  327. 

  328. person<span class="token punctuation">.</span><span class="token function">facepalmWithoutWarning</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    329. 

  329. <span class="token comment">// no warning is logged</span>
    330. 

  330. </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></div></div><h2 id="使用装饰器实现自动发布事件"><a href="#使用装饰器实现自动发布事件" class="header-anchor">#</a> 使用装饰器实现自动发布事件</h2> <p>我们可以使用装饰器，使得对象的方法被调用时，自动发出一个事件。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> postal <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">&quot;postal/lib/postal.lodash&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    331. 

  331. 

  332. <span class="token keyword">export</span> <span class="token keyword">default</span> <span class="token keyword">function</span> <span class="token function">publish</span><span class="token punctuation">(</span><span class="token parameter">topic<span class="token punctuation">,</span> channel</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    333. 

  333.   <span class="token keyword">const</span> channelName <span class="token operator">=</span> channel <span class="token operator">||</span> <span class="token string">'/'</span><span class="token punctuation">;</span>
    334. 

  334.   <span class="token keyword">const</span> msgChannel <span class="token operator">=</span> postal<span class="token punctuation">.</span><span class="token function">channel</span><span class="token punctuation">(</span>channelName<span class="token punctuation">)</span><span class="token punctuation">;</span>
    335. 

  335.   msgChannel<span class="token punctuation">.</span><span class="token function">subscribe</span><span class="token punctuation">(</span>topic<span class="token punctuation">,</span> <span class="token parameter">v</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
    336. 

  336.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'频道: '</span><span class="token punctuation">,</span> channelName<span class="token punctuation">)</span><span class="token punctuation">;</span>
    337. 

  337.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'事件: '</span><span class="token punctuation">,</span> topic<span class="token punctuation">)</span><span class="token punctuation">;</span>
    338. 

  338.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'数据: '</span><span class="token punctuation">,</span> v<span class="token punctuation">)</span><span class="token punctuation">;</span>
    339. 

  339.   <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    340. 

  340. 

  341.   <span class="token keyword">return</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter">target<span class="token punctuation">,</span> name<span class="token punctuation">,</span> descriptor</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    342. 

  342.     <span class="token keyword">const</span> fn <span class="token operator">=</span> descriptor<span class="token punctuation">.</span>value<span class="token punctuation">;</span>
    343. 

  343. 

  344.     descriptor<span class="token punctuation">.</span><span class="token function-variable function">value</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    345. 

  345.       <span class="token keyword">let</span> value <span class="token operator">=</span> <span class="token function">fn</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">,</span> arguments<span class="token punctuation">)</span><span class="token punctuation">;</span>
    346. 

  346.       msgChannel<span class="token punctuation">.</span><span class="token function">publish</span><span class="token punctuation">(</span>topic<span class="token punctuation">,</span> value<span class="token punctuation">)</span><span class="token punctuation">;</span>
    347. 

  347.     <span class="token punctuation">}</span><span class="token punctuation">;</span>
    348. 

  348.   <span class="token punctuation">}</span><span class="token punctuation">;</span>
    349. 

  349. <span class="token punctuation">}</span>
    350. 

  350. </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></div></div><p>上面代码定义了一个名为<code>publish</code>的装饰器，它通过改写<code>descriptor.value</code>，使得原方法被调用时，会自动发出一个事件。它使用的事件“发布/订阅”库是<a href="https://github.com/postaljs/postal.js" target="_blank" rel="noopener noreferrer">Postal.js<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> <p>它的用法如下。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// index.js</span>
    351. 

  351. <span class="token keyword">import</span> publish <span class="token keyword">from</span> <span class="token string">'./publish'</span><span class="token punctuation">;</span>
    352. 

  352. 

  353. <span class="token keyword">class</span> <span class="token class-name">FooComponent</span> <span class="token punctuation">{</span>
    354. 

  354.   @<span class="token function">publish</span><span class="token punctuation">(</span><span class="token string">'foo.some.message'</span><span class="token punctuation">,</span> <span class="token string">'component'</span><span class="token punctuation">)</span>
    355. 

  355.   <span class="token function">someMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    356. 

  356.     <span class="token keyword">return</span> <span class="token punctuation">{</span> <span class="token literal-property property">my</span><span class="token operator">:</span> <span class="token string">'data'</span> <span class="token punctuation">}</span><span class="token punctuation">;</span>
    357. 

  357.   <span class="token punctuation">}</span>
    358. 

  358.   @<span class="token function">publish</span><span class="token punctuation">(</span><span class="token string">'foo.some.other'</span><span class="token punctuation">)</span>
    359. 

  359.   <span class="token function">anotherMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    360. 

  360.     <span class="token comment">// ...</span>
    361. 

  361.   <span class="token punctuation">}</span>
    362. 

  362. <span class="token punctuation">}</span>
    363. 

  363. 

  364. <span class="token keyword">let</span> foo <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FooComponent</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    365. 

  365. 

  366. foo<span class="token punctuation">.</span><span class="token function">someMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    367. 

  367. foo<span class="token punctuation">.</span><span class="token function">anotherMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    368. 

  368. </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></div></div><p>以后，只要调用<code>someMethod</code>或者<code>anotherMethod</code>，就会自动发出一个事件。</p> <div class="language-bash line-numbers-mode"><pre class="language-bash"><code>$ bash-node index.js
    369. 

  369. 频道:  component
    370. 

  370. 事件:  foo.some.message
    371. 

  371. 数据:  <span class="token punctuation">{</span> my: <span class="token string">'data'</span> <span class="token punctuation">}</span>
    372. 

  372. 

  373. 频道:  /
    374. 

  374. 事件:  foo.some.other
    375. 

  375. 数据:  undefined
    376. 

  376. </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></div></div><h2 id="mixin"><a href="#mixin" class="header-anchor">#</a> Mixin</h2> <p>在装饰器的基础上，可以实现<code>Mixin</code>模式。所谓<code>Mixin</code>模式，就是对象继承的一种替代方案，中文译为“混入”（mix in），意为在一个对象之中混入另外一个对象的方法。</p> <p>请看下面的例子。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> Foo <span class="token operator">=</span> <span class="token punctuation">{</span>
    377. 

  377.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    378. 

  378. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    379. 

  379. 

  380. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    381. 

  381. 

  382. Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span><span class="token class-name">MyClass</span><span class="token punctuation">.</span>prototype<span class="token punctuation">,</span> Foo<span class="token punctuation">)</span><span class="token punctuation">;</span>
    383. 

  383. 

  384. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    385. 

  385. obj<span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// 'foo'</span>
    386. 

  386. </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></div></div><p>上面代码之中，对象<code>Foo</code>有一个<code>foo</code>方法，通过<code>Object.assign</code>方法，可以将<code>foo</code>方法“混入”<code>MyClass</code>类，导致<code>MyClass</code>的实例<code>obj</code>对象都具有<code>foo</code>方法。这就是“混入”模式的一个简单实现。</p> <p>下面，我们部署一个通用脚本<code>mixins.js</code>，将 Mixin 写成一个装饰器。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">export</span> <span class="token keyword">function</span> <span class="token function">mixins</span><span class="token punctuation">(</span><span class="token parameter"><span class="token operator">...</span>list</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    387. 

  387.   <span class="token keyword">return</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">target</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    388. 

  388.     Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span>target<span class="token punctuation">.</span>prototype<span class="token punctuation">,</span> <span class="token operator">...</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
    389. 

  389.   <span class="token punctuation">}</span><span class="token punctuation">;</span>
    390. 

  390. <span class="token punctuation">}</span>
    391. 

  391. </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></div></div><p>然后，就可以使用上面这个装饰器，为类“混入”各种方法。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> mixins <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'./mixins'</span><span class="token punctuation">;</span>
    392. 

  392. 

  393. <span class="token keyword">const</span> Foo <span class="token operator">=</span> <span class="token punctuation">{</span>
    394. 

  394.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    395. 

  395. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    396. 

  396. 

  397. @<span class="token function">mixins</span><span class="token punctuation">(</span>Foo<span class="token punctuation">)</span>
    398. 

  398. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    399. 

  399. 

  400. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    401. 

  401. obj<span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// &quot;foo&quot;</span>
    402. 

  402. </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></div></div><p>通过<code>mixins</code>这个装饰器，实现了在<code>MyClass</code>类上面“混入”<code>Foo</code>对象的<code>foo</code>方法。</p> <p>不过，上面的方法会改写<code>MyClass</code>类的<code>prototype</code>对象，如果不喜欢这一点，也可以通过类的继承实现 Mixin。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token keyword">extends</span> <span class="token class-name">MyBaseClass</span> <span class="token punctuation">{</span>
    403. 

  403.   <span class="token comment">/* ... */</span>
    404. 

  404. <span class="token punctuation">}</span>
    405. 

  405. </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><p>上面代码中，<code>MyClass</code>继承了<code>MyBaseClass</code>。如果我们想在<code>MyClass</code>里面“混入”一个<code>foo</code>方法，一个办法是在<code>MyClass</code>和<code>MyBaseClass</code>之间插入一个混入类，这个类具有<code>foo</code>方法，并且继承了<code>MyBaseClass</code>的所有方法，然后<code>MyClass</code>再继承这个类。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">let</span> <span class="token function-variable function">MyMixin</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter">superclass</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token keyword">class</span> <span class="token class-name">extends</span> superclass <span class="token punctuation">{</span>
    406. 

  406.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    407. 

  407.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo from MyMixin'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    408. 

  408.   <span class="token punctuation">}</span>
    409. 

  409. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    410. 

  410. </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></div></div><p>上面代码中，<code>MyMixin</code>是一个混入类生成器，接受<code>superclass</code>作为参数，然后返回一个继承<code>superclass</code>的子类，该子类包含一个<code>foo</code>方法。</p> <p>接着，目标类再去继承这个混入类，就达到了“混入”<code>foo</code>方法的目的。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token keyword">extends</span> <span class="token class-name">MyMixin</span><span class="token punctuation">(</span>MyBaseClass<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    411. 

  411.   <span class="token comment">/* ... */</span>
    412. 

  412. <span class="token punctuation">}</span>
    413. 

  413. 

  414. <span class="token keyword">let</span> c <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    415. 

  415. c<span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// &quot;foo from MyMixin&quot;</span>
    416. 

  416. </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></div></div><p>如果需要“混入”多个方法，就生成多个混入类。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token keyword">extends</span> <span class="token class-name">Mixin1</span><span class="token punctuation">(</span><span class="token function">Mixin2</span><span class="token punctuation">(</span>MyBaseClass<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    417. 

  417.   <span class="token comment">/* ... */</span>
    418. 

  418. <span class="token punctuation">}</span>
    419. 

  419. </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><p>这种写法的一个好处，是可以调用<code>super</code>，因此可以避免在“混入”过程中覆盖父类的同名方法。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">let</span> <span class="token function-variable function">Mixin1</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter">superclass</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token keyword">class</span> <span class="token class-name">extends</span> superclass <span class="token punctuation">{</span>
    420. 

  420.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    421. 

  421.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo from Mixin1'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    422. 

  422.     <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">super</span><span class="token punctuation">.</span>foo<span class="token punctuation">)</span> <span class="token keyword">super</span><span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    423. 

  423.   <span class="token punctuation">}</span>
    424. 

  424. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    425. 

  425. 

  426. <span class="token keyword">let</span> <span class="token function-variable function">Mixin2</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter">superclass</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token keyword">class</span> <span class="token class-name">extends</span> superclass <span class="token punctuation">{</span>
    427. 

  427.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    428. 

  428.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo from Mixin2'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    429. 

  429.     <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">super</span><span class="token punctuation">.</span>foo<span class="token punctuation">)</span> <span class="token keyword">super</span><span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    430. 

  430.   <span class="token punctuation">}</span>
    431. 

  431. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    432. 

  432. 

  433. <span class="token keyword">class</span> <span class="token class-name">S</span> <span class="token punctuation">{</span>
    434. 

  434.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    435. 

  435.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo from S'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    436. 

  436.   <span class="token punctuation">}</span>
    437. 

  437. <span class="token punctuation">}</span>
    438. 

  438. 

  439. <span class="token keyword">class</span> <span class="token class-name">C</span> <span class="token keyword">extends</span> <span class="token class-name">Mixin1</span><span class="token punctuation">(</span><span class="token function">Mixin2</span><span class="token punctuation">(</span><span class="token constant">S</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    440. 

  440.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    441. 

  441.     console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo from C'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    442. 

  442.     <span class="token keyword">super</span><span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    443. 

  443.   <span class="token punctuation">}</span>
    444. 

  444. <span class="token punctuation">}</span>
    445. 

  445. </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 class="line-number">25</span><br><span class="line-number">26</span><br></div></div><p>上面代码中，每一次<code>混入</code>发生时，都调用了父类的<code>super.foo</code>方法，导致父类的同名方法没有被覆盖，行为被保留了下来。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">new</span> <span class="token class-name">C</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
    446. 

  446. <span class="token comment">// foo from C</span>
    447. 

  447. <span class="token comment">// foo from Mixin1</span>
    448. 

  448. <span class="token comment">// foo from Mixin2</span>
    449. 

  449. <span class="token comment">// foo from S</span>
    450. 

  450. </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></div></div><h2 id="trait"><a href="#trait" class="header-anchor">#</a> Trait</h2> <p>Trait 也是一种装饰器，效果与 Mixin 类似，但是提供更多功能，比如防止同名方法的冲突、排除混入某些方法、为混入的方法起别名等等。</p> <p>下面采用<a href="https://github.com/CocktailJS/traits-decorator" target="_blank" rel="noopener noreferrer">traits-decorator<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>这个第三方模块作为例子。这个模块提供的<code>traits</code>装饰器，不仅可以接受对象，还可以接受 ES6 类作为参数。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> traits <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'traits-decorator'</span><span class="token punctuation">;</span>
    451. 

  451. 

  452. <span class="token keyword">class</span> <span class="token class-name">TFoo</span> <span class="token punctuation">{</span>
    453. 

  453.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    454. 

  454. <span class="token punctuation">}</span>
    455. 

  455. 

  456. <span class="token keyword">const</span> TBar <span class="token operator">=</span> <span class="token punctuation">{</span>
    457. 

  457.   <span class="token function">bar</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'bar'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    458. 

  458. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    459. 

  459. 

  460. @<span class="token function">traits</span><span class="token punctuation">(</span>TFoo<span class="token punctuation">,</span> TBar<span class="token punctuation">)</span>
    461. 

  461. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span> <span class="token punctuation">}</span>
    462. 

  462. 

  463. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    464. 

  464. obj<span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// foo</span>
    465. 

  465. obj<span class="token punctuation">.</span><span class="token function">bar</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// bar</span>
    466. 

  466. </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></div></div><p>上面代码中，通过<code>traits</code>装饰器，在<code>MyClass</code>类上面“混入”了<code>TFoo</code>类的<code>foo</code>方法和<code>TBar</code>对象的<code>bar</code>方法。</p> <p>Trait 不允许“混入”同名方法。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> traits <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'traits-decorator'</span><span class="token punctuation">;</span>
    467. 

  467. 

  468. <span class="token keyword">class</span> <span class="token class-name">TFoo</span> <span class="token punctuation">{</span>
    469. 

  469.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    470. 

  470. <span class="token punctuation">}</span>
    471. 

  471. 

  472. <span class="token keyword">const</span> TBar <span class="token operator">=</span> <span class="token punctuation">{</span>
    473. 

  473.   <span class="token function">bar</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'bar'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span><span class="token punctuation">,</span>
    474. 

  474.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    475. 

  475. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    476. 

  476. 

  477. @<span class="token function">traits</span><span class="token punctuation">(</span>TFoo<span class="token punctuation">,</span> TBar<span class="token punctuation">)</span>
    478. 

  478. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span> <span class="token punctuation">}</span>
    479. 

  479. <span class="token comment">// 报错</span>
    480. 

  480. <span class="token comment">// throw new Error('Method named: ' + methodName + ' is defined twice.');</span>
    481. 

  481. <span class="token comment">//        ^</span>
    482. 

  482. <span class="token comment">// Error: Method named: foo is defined twice.</span>
    483. 

  483. </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></div></div><p>上面代码中，<code>TFoo</code>和<code>TBar</code>都有<code>foo</code>方法，结果<code>traits</code>装饰器报错。</p> <p>一种解决方法是排除<code>TBar</code>的<code>foo</code>方法。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> traits<span class="token punctuation">,</span> excludes <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'traits-decorator'</span><span class="token punctuation">;</span>
    484. 

  484. 

  485. <span class="token keyword">class</span> <span class="token class-name">TFoo</span> <span class="token punctuation">{</span>
    486. 

  486.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    487. 

  487. <span class="token punctuation">}</span>
    488. 

  488. 

  489. <span class="token keyword">const</span> TBar <span class="token operator">=</span> <span class="token punctuation">{</span>
    490. 

  490.   <span class="token function">bar</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'bar'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span><span class="token punctuation">,</span>
    491. 

  491.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    492. 

  492. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    493. 

  493. 

  494. @<span class="token function">traits</span><span class="token punctuation">(</span>TFoo<span class="token punctuation">,</span> <span class="token literal-property property">TBar</span><span class="token operator">:</span><span class="token operator">:</span><span class="token function">excludes</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    495. 

  495. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span> <span class="token punctuation">}</span>
    496. 

  496. 

  497. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    498. 

  498. obj<span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// foo</span>
    499. 

  499. obj<span class="token punctuation">.</span><span class="token function">bar</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// bar</span>
    500. 

  500. </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></div></div><p>上面代码使用绑定运算符（::）在<code>TBar</code>上排除<code>foo</code>方法，混入时就不会报错了。</p> <p>另一种方法是为<code>TBar</code>的<code>foo</code>方法起一个别名。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">import</span> <span class="token punctuation">{</span> traits<span class="token punctuation">,</span> alias <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'traits-decorator'</span><span class="token punctuation">;</span>
    501. 

  501. 

  502. <span class="token keyword">class</span> <span class="token class-name">TFoo</span> <span class="token punctuation">{</span>
    503. 

  503.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    504. 

  504. <span class="token punctuation">}</span>
    505. 

  505. 

  506. <span class="token keyword">const</span> TBar <span class="token operator">=</span> <span class="token punctuation">{</span>
    507. 

  507.   <span class="token function">bar</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'bar'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span><span class="token punctuation">,</span>
    508. 

  508.   <span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">)</span> <span class="token punctuation">}</span>
    509. 

  509. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    510. 

  510. 

  511. @<span class="token function">traits</span><span class="token punctuation">(</span>TFoo<span class="token punctuation">,</span> <span class="token literal-property property">TBar</span><span class="token operator">:</span><span class="token operator">:</span><span class="token function">alias</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token literal-property property">foo</span><span class="token operator">:</span> <span class="token string">'aliasFoo'</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    512. 

  512. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span> <span class="token punctuation">}</span>
    513. 

  513. 

  514. <span class="token keyword">let</span> obj <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyClass</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    515. 

  515. obj<span class="token punctuation">.</span><span class="token function">foo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// foo</span>
    516. 

  516. obj<span class="token punctuation">.</span><span class="token function">aliasFoo</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// foo</span>
    517. 

  517. obj<span class="token punctuation">.</span><span class="token function">bar</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token comment">// bar</span>
    518. 

  518. </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></div></div><p>上面代码为<code>TBar</code>的<code>foo</code>方法起了别名<code>aliasFoo</code>，于是<code>MyClass</code>也可以混入<code>TBar</code>的<code>foo</code>方法了。</p> <p><code>alias</code>和<code>excludes</code>方法，可以结合起来使用。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>@<span class="token function">traits</span><span class="token punctuation">(</span>TExample<span class="token operator">:</span><span class="token operator">:</span><span class="token function">excludes</span><span class="token punctuation">(</span><span class="token string">'foo'</span><span class="token punctuation">,</span><span class="token string">'bar'</span><span class="token punctuation">)</span><span class="token operator">:</span><span class="token operator">:</span><span class="token function">alias</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token literal-property property">baz</span><span class="token operator">:</span><span class="token string">'exampleBaz'</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    519. 

  519. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    520. 

  520. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>上面代码排除了<code>TExample</code>的<code>foo</code>方法和<code>bar</code>方法，为<code>baz</code>方法起了别名<code>exampleBaz</code>。</p> <p><code>as</code>方法则为上面的代码提供了另一种写法。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code>@<span class="token function">traits</span><span class="token punctuation">(</span>TExample<span class="token operator">:</span><span class="token operator">:</span><span class="token keyword">as</span><span class="token punctuation">(</span><span class="token punctuation">{</span><span class="token literal-property property">excludes</span><span class="token operator">:</span><span class="token punctuation">[</span><span class="token string">'foo'</span><span class="token punctuation">,</span> <span class="token string">'bar'</span><span class="token punctuation">]</span><span class="token punctuation">,</span> <span class="token literal-property property">alias</span><span class="token operator">:</span> <span class="token punctuation">{</span><span class="token literal-property property">baz</span><span class="token operator">:</span> <span class="token string">'exampleBaz'</span><span class="token punctuation">}</span><span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    521. 

  521. <span class="token keyword">class</span> <span class="token class-name">MyClass</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>
    522. 

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