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href="/blog/note/es6/#《ES6 教程》笔记" data-v-06225672>《ES6 教程》笔记</a></li></ul> <div class="info" data-v-06225672><div title="作者" class="author iconfont icon-touxiang" data-v-06225672><a href="javascript:;" data-v-06225672>阮一峰</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>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,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">编程风格<!----></h1>  <div class="theme-vdoing-content content__default"><h1 id="编程风格"><a href="#编程风格" class="header-anchor">#</a> 编程风格</h1> <p>本章探讨如何将 ES6 的新语法，运用到编码实践之中，与传统的 JavaScript 语法结合在一起，写出合理的、易于阅读和维护的代码。</p> <p>多家公司和组织已经公开了它们的风格规范，下面的内容主要参考了 <a href="https://github.com/airbnb/javascript" target="_blank" rel="noopener noreferrer">Airbnb<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> 公司的 JavaScript 风格规范。
    26. 

  26. </p> <h2 id="块级作用域"><a href="#块级作用域" class="header-anchor">#</a> 块级作用域</h2> <p><strong>（1）let 取代 var</strong></p> <p>ES6 提出了两个新的声明变量的命令：<code>let</code>和<code>const</code>。其中，<code>let</code>完全可以取代<code>var</code>，因为两者语义相同，而且<code>let</code>没有副作用。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token string">'use strict'</span><span class="token punctuation">;</span>
    27. 

  27. 

  28. <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    29. 

  29.   <span class="token keyword">let</span> x <span class="token operator">=</span> <span class="token string">'hello'</span><span class="token punctuation">;</span>
    30. 

  30. <span class="token punctuation">}</span>
    31. 

  31. 

  32. <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> <span class="token number">10</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    33. 

  33.   console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>i<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><span class="line-number">9</span><br></div></div><p>上面代码如果用<code>var</code>替代<code>let</code>，实际上就声明了两个全局变量，这显然不是本意。变量应该只在其声明的代码块内有效，<code>var</code>命令做不到这一点。</p> <p><code>var</code>命令存在变量提升效用，<code>let</code>命令没有这个问题。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token string">'use strict'</span><span class="token punctuation">;</span>
    36. 

  36. 

  37. <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    38. 

  38.   console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>x<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// ReferenceError</span>
    39. 

  39.   <span class="token keyword">let</span> x <span class="token operator">=</span> <span class="token string">'hello'</span><span class="token punctuation">;</span>
    40. 

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

  41. </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>上面代码如果使用<code>var</code>替代<code>let</code>，<code>console.log</code>那一行就不会报错，而是会输出<code>undefined</code>，因为变量声明提升到代码块的头部。这违反了变量先声明后使用的原则。</p> <p>所以，建议不再使用<code>var</code>命令，而是使用<code>let</code>命令取代。</p> <p><strong>（2）全局常量和线程安全</strong></p> <p>在<code>let</code>和<code>const</code>之间，建议优先使用<code>const</code>，尤其是在全局环境，不应该设置变量，只应设置常量。</p> <p><code>const</code>优于<code>let</code>有几个原因。一个是<code>const</code>可以提醒阅读程序的人，这个变量不应该改变；另一个是<code>const</code>比较符合函数式编程思想，运算不改变值，只是新建值，而且这样也有利于将来的分布式运算；最后一个原因是 JavaScript <strong>编译器会对<code>const</code>进行优化</strong>，所以多使用<code>const</code>，有利于提高程序的运行效率，也就是说<code>let</code>和<code>const</code>的本质区别，其实是编译器内部的处理不同。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    42. 

  42. <span class="token keyword">var</span> a <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">,</span> b <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">,</span> c <span class="token operator">=</span> <span class="token number">3</span><span class="token punctuation">;</span>
    43. 

  43. 

  44. <span class="token comment">// good</span>
    45. 

  45. <span class="token keyword">const</span> a <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>
    46. 

  46. <span class="token keyword">const</span> b <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
    47. 

  47. <span class="token keyword">const</span> c <span class="token operator">=</span> <span class="token number">3</span><span class="token punctuation">;</span>
    48. 

  48. 

  49. <span class="token comment">// best</span>
    50. 

  50. <span class="token keyword">const</span> <span class="token punctuation">[</span>a<span class="token punctuation">,</span> b<span class="token punctuation">,</span> c<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    51. 

  51. </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><code>const</code>声明常量还有两个好处，一是阅读代码的人立刻会意识到不应该修改这个值，二是防止了无意间修改变量值所导致的错误。</p> <p>所有的函数都应该设置为常量。</p> <p>长远来看，JavaScript 可能会有多线程的实现（比如 Intel 公司的 River Trail 那一类的项目），这时<code>let</code>表示的变量，只应出现在单线程运行的代码中，不能是多线程共享的，这样有利于保证线程安全。</p> <h2 id="字符串"><a href="#字符串" class="header-anchor">#</a> 字符串</h2> <p>静态字符串一律使用单引号或反引号，不使用双引号。动态字符串使用反引号。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    52. 

  52. <span class="token keyword">const</span> a <span class="token operator">=</span> <span class="token string">&quot;foobar&quot;</span><span class="token punctuation">;</span>
    53. 

  53. <span class="token keyword">const</span> b <span class="token operator">=</span> <span class="token string">'foo'</span> <span class="token operator">+</span> a <span class="token operator">+</span> <span class="token string">'bar'</span><span class="token punctuation">;</span>
    54. 

  54. 

  55. <span class="token comment">// acceptable</span>
    56. 

  56. <span class="token keyword">const</span> c <span class="token operator">=</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">foobar</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">;</span>
    57. 

  57. 

  58. <span class="token comment">// good</span>
    59. 

  59. <span class="token keyword">const</span> a <span class="token operator">=</span> <span class="token string">'foobar'</span><span class="token punctuation">;</span>
    60. 

  60. <span class="token keyword">const</span> b <span class="token operator">=</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">foo</span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>a<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string">bar</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">;</span>
    61. 

  61. </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><h2 id="解构赋值"><a href="#解构赋值" class="header-anchor">#</a> 解构赋值</h2> <p>使用数组成员对变量赋值时，优先使用解构赋值。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> arr <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    62. 

  62. 

  63. <span class="token comment">// bad</span>
    64. 

  64. <span class="token keyword">const</span> first <span class="token operator">=</span> arr<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    65. 

  65. <span class="token keyword">const</span> second <span class="token operator">=</span> arr<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    66. 

  66. 

  67. <span class="token comment">// good</span>
    68. 

  68. <span class="token keyword">const</span> <span class="token punctuation">[</span>first<span class="token punctuation">,</span> second<span class="token punctuation">]</span> <span class="token operator">=</span> arr<span class="token punctuation">;</span>
    69. 

  69. </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>函数的参数如果是对象的成员，优先使用解构赋值。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    70. 

  70. <span class="token keyword">function</span> <span class="token function">getFullName</span><span class="token punctuation">(</span><span class="token parameter">user</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    71. 

  71.   <span class="token keyword">const</span> firstName <span class="token operator">=</span> user<span class="token punctuation">.</span>firstName<span class="token punctuation">;</span>
    72. 

  72.   <span class="token keyword">const</span> lastName <span class="token operator">=</span> user<span class="token punctuation">.</span>lastName<span class="token punctuation">;</span>
    73. 

  73. <span class="token punctuation">}</span>
    74. 

  74. 

  75. <span class="token comment">// good</span>
    76. 

  76. <span class="token keyword">function</span> <span class="token function">getFullName</span><span class="token punctuation">(</span><span class="token parameter">obj</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    77. 

  77.   <span class="token keyword">const</span> <span class="token punctuation">{</span> firstName<span class="token punctuation">,</span> lastName <span class="token punctuation">}</span> <span class="token operator">=</span> obj<span class="token punctuation">;</span>
    78. 

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

  79. 

  80. <span class="token comment">// best</span>
    81. 

  81. <span class="token keyword">function</span> <span class="token function">getFullName</span><span class="token punctuation">(</span><span class="token parameter"><span class="token punctuation">{</span> firstName<span class="token punctuation">,</span> lastName <span class="token punctuation">}</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    82. 

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

  83. </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>如果函数返回多个值，优先使用对象的解构赋值，而不是数组的解构赋值。这样便于以后添加返回值，以及更改返回值的顺序。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    84. 

  84. <span class="token keyword">function</span> <span class="token function">processInput</span><span class="token punctuation">(</span><span class="token parameter">input</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    85. 

  85.   <span class="token keyword">return</span> <span class="token punctuation">[</span>left<span class="token punctuation">,</span> right<span class="token punctuation">,</span> top<span class="token punctuation">,</span> bottom<span class="token punctuation">]</span><span class="token punctuation">;</span>
    86. 

  86. <span class="token punctuation">}</span>
    87. 

  87. 

  88. <span class="token comment">// good</span>
    89. 

  89. <span class="token keyword">function</span> <span class="token function">processInput</span><span class="token punctuation">(</span><span class="token parameter">input</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    90. 

  90.   <span class="token keyword">return</span> <span class="token punctuation">{</span> left<span class="token punctuation">,</span> right<span class="token punctuation">,</span> top<span class="token punctuation">,</span> bottom <span class="token punctuation">}</span><span class="token punctuation">;</span>
    91. 

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

  92. 

  93. <span class="token keyword">const</span> <span class="token punctuation">{</span> left<span class="token punctuation">,</span> right <span class="token punctuation">}</span> <span class="token operator">=</span> <span class="token function">processInput</span><span class="token punctuation">(</span>input<span class="token punctuation">)</span><span class="token punctuation">;</span>
    94. 

  94. </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><h2 id="对象"><a href="#对象" class="header-anchor">#</a> 对象</h2> <p>单行定义的对象，最后一个成员不以逗号结尾。多行定义的对象，<strong>最后一个成员以逗号结尾</strong>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    95. 

  95. <span class="token keyword">const</span> a <span class="token operator">=</span> <span class="token punctuation">{</span> <span class="token literal-property property">k1</span><span class="token operator">:</span> v1<span class="token punctuation">,</span> <span class="token literal-property property">k2</span><span class="token operator">:</span> v2<span class="token punctuation">,</span> <span class="token punctuation">}</span><span class="token punctuation">;</span>
    96. 

  96. <span class="token keyword">const</span> b <span class="token operator">=</span> <span class="token punctuation">{</span>
    97. 

  97.   <span class="token literal-property property">k1</span><span class="token operator">:</span> v1<span class="token punctuation">,</span>
    98. 

  98.   <span class="token literal-property property">k2</span><span class="token operator">:</span> v2
    99. 

  99. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    100. 

  100. 

  101. <span class="token comment">// good</span>
    102. 

  102. <span class="token keyword">const</span> a <span class="token operator">=</span> <span class="token punctuation">{</span> <span class="token literal-property property">k1</span><span class="token operator">:</span> v1<span class="token punctuation">,</span> <span class="token literal-property property">k2</span><span class="token operator">:</span> v2 <span class="token punctuation">}</span><span class="token punctuation">;</span>
    103. 

  103. <span class="token keyword">const</span> b <span class="token operator">=</span> <span class="token punctuation">{</span>
    104. 

  104.   <span class="token literal-property property">k1</span><span class="token operator">:</span> v1<span class="token punctuation">,</span>
    105. 

  105.   <span class="token literal-property property">k2</span><span class="token operator">:</span> v2<span class="token punctuation">,</span>
    106. 

  106. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    107. 

  107. </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>对象尽量静态化，一旦定义，就不得随意添加新的属性。如果添加属性不可避免，要使用<code>Object.assign</code>方法。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    108. 

  108. <span class="token keyword">const</span> a <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
    109. 

  109. a<span class="token punctuation">.</span>x <span class="token operator">=</span> <span class="token number">3</span><span class="token punctuation">;</span>
    110. 

  110. 

  111. <span class="token comment">// if reshape unavoidable</span>
    112. 

  112. <span class="token keyword">const</span> a <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
    113. 

  113. Object<span class="token punctuation">.</span><span class="token function">assign</span><span class="token punctuation">(</span>a<span class="token punctuation">,</span> <span class="token punctuation">{</span> <span class="token literal-property property">x</span><span class="token operator">:</span> <span class="token number">3</span> <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    114. 

  114. 

  115. <span class="token comment">// good</span>
    116. 

  116. <span class="token keyword">const</span> a <span class="token operator">=</span> <span class="token punctuation">{</span> <span class="token literal-property property">x</span><span class="token operator">:</span> <span class="token keyword">null</span> <span class="token punctuation">}</span><span class="token punctuation">;</span>
    117. 

  117. a<span class="token punctuation">.</span>x <span class="token operator">=</span> <span class="token number">3</span><span class="token punctuation">;</span>
    118. 

  118. </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>如果对象的属性名是动态的，可以在创造对象的时候，使用属性表达式定义。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    119. 

  119. <span class="token keyword">const</span> obj <span class="token operator">=</span> <span class="token punctuation">{</span>
    120. 

  120.   <span class="token literal-property property">id</span><span class="token operator">:</span> <span class="token number">5</span><span class="token punctuation">,</span>
    121. 

  121.   <span class="token literal-property property">name</span><span class="token operator">:</span> <span class="token string">'San Francisco'</span><span class="token punctuation">,</span>
    122. 

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

  123. obj<span class="token punctuation">[</span><span class="token function">getKey</span><span class="token punctuation">(</span><span class="token string">'enabled'</span><span class="token punctuation">)</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
    124. 

  124. 

  125. <span class="token comment">// good</span>
    126. 

  126. <span class="token keyword">const</span> obj <span class="token operator">=</span> <span class="token punctuation">{</span>
    127. 

  127.   <span class="token literal-property property">id</span><span class="token operator">:</span> <span class="token number">5</span><span class="token punctuation">,</span>
    128. 

  128.   <span class="token literal-property property">name</span><span class="token operator">:</span> <span class="token string">'San Francisco'</span><span class="token punctuation">,</span>
    129. 

  129.   <span class="token punctuation">[</span><span class="token function">getKey</span><span class="token punctuation">(</span><span class="token string">'enabled'</span><span class="token punctuation">)</span><span class="token punctuation">]</span><span class="token operator">:</span> <span class="token boolean">true</span><span class="token punctuation">,</span>
    130. 

  130. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    131. 

  131. </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，对象<code>obj</code>的最后一个属性名，需要计算得到。这时最好采用属性表达式，在新建<code>obj</code>的时候，将该属性与其他属性定义在一起。这样一来，所有属性就在一个地方定义了。</p> <p>另外，对象的属性和方法，<strong>尽量采用简洁表达法</strong>，这样易于描述和书写。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> ref <span class="token operator">=</span> <span class="token string">'some value'</span><span class="token punctuation">;</span>
    132. 

  132. 

  133. <span class="token comment">// bad</span>
    134. 

  134. <span class="token keyword">const</span> atom <span class="token operator">=</span> <span class="token punctuation">{</span>
    135. 

  135.   <span class="token literal-property property">ref</span><span class="token operator">:</span> ref<span class="token punctuation">,</span>
    136. 

  136. 

  137.   <span class="token literal-property property">value</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span>
    138. 

  138. 

  139.   <span class="token function-variable function">addValue</span><span class="token operator">:</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">value</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    140. 

  140.     <span class="token keyword">return</span> atom<span class="token punctuation">.</span>value <span class="token operator">+</span> value<span class="token punctuation">;</span>
    141. 

  141.   <span class="token punctuation">}</span><span class="token punctuation">,</span>
    142. 

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

  143. 

  144. <span class="token comment">// good</span>
    145. 

  145. <span class="token keyword">const</span> atom <span class="token operator">=</span> <span class="token punctuation">{</span>
    146. 

  146.   ref<span class="token punctuation">,</span>
    147. 

  147. 

  148.   <span class="token literal-property property">value</span><span class="token operator">:</span> <span class="token number">1</span><span class="token punctuation">,</span>
    149. 

  149. 

  150.   <span class="token function">addValue</span><span class="token punctuation">(</span><span class="token parameter">value</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    151. 

  151.     <span class="token keyword">return</span> atom<span class="token punctuation">.</span>value <span class="token operator">+</span> value<span class="token punctuation">;</span>
    152. 

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

  153. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    154. 

  154. </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></div></div><h2 id="数组"><a href="#数组" class="header-anchor">#</a> 数组</h2> <p>使用<strong>扩展运算符（...）拷贝数组</strong>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    155. 

  155. <span class="token keyword">const</span> len <span class="token operator">=</span> items<span class="token punctuation">.</span>length<span class="token punctuation">;</span>
    156. 

  156. <span class="token keyword">const</span> itemsCopy <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    157. 

  157. <span class="token keyword">let</span> i<span class="token punctuation">;</span>
    158. 

  158. 

  159. <span class="token keyword">for</span> <span class="token punctuation">(</span>i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> len<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    160. 

  160.   itemsCopy<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">=</span> items<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
    161. 

  161. <span class="token punctuation">}</span>
    162. 

  162. 

  163. <span class="token comment">// good</span>
    164. 

  164. <span class="token keyword">const</span> itemsCopy <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token operator">...</span>items<span class="token punctuation">]</span><span class="token punctuation">;</span>
    165. 

  165. </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>使用 <strong>Array.from 方法，将类似数组的对象转为数组</strong>。</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> document<span class="token punctuation">.</span><span class="token function">querySelectorAll</span><span class="token punctuation">(</span><span class="token string">'.foo'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    166. 

  166. <span class="token keyword">const</span> nodes <span class="token operator">=</span> Array<span class="token punctuation">.</span><span class="token function">from</span><span class="token punctuation">(</span>foo<span class="token punctuation">)</span><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></div></div><h2 id="函数"><a href="#函数" class="header-anchor">#</a> 函数</h2> <p>立即执行函数可以写成箭头函数的形式。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
    168. 

  168.   console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">'Welcome to the Internet.'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    169. 

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

  170. </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>那些使用匿名函数当作参数的场合，<strong>尽量用箭头函数代替</strong>。因为这样更简洁，而且绑定了 this。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    171. 

  171. <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">x</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    172. 

  172.   <span class="token keyword">return</span> x <span class="token operator">*</span> x<span class="token punctuation">;</span>
    173. 

  173. <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    174. 

  174. 

  175. <span class="token comment">// good</span>
    176. 

  176. <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token parameter">x</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
    177. 

  177.   <span class="token keyword">return</span> x <span class="token operator">*</span> x<span class="token punctuation">;</span>
    178. 

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

  179. 

  180. <span class="token comment">// best</span>
    181. 

  181. <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span><span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token parameter">x</span> <span class="token operator">=&gt;</span> x <span class="token operator">*</span> x<span class="token punctuation">)</span><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></div></div><p>箭头函数取代<code>Function.prototype.bind</code>，不应再用 self/_this/that 绑定 this。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    183. 

  183. <span class="token keyword">const</span> self <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">;</span>
    184. 

  184. <span class="token keyword">const</span> <span class="token function-variable function">boundMethod</span> <span class="token operator">=</span> <span class="token keyword">function</span><span class="token punctuation">(</span><span class="token parameter"><span class="token operator">...</span>params</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    185. 

  185.   <span class="token keyword">return</span> <span class="token function">method</span><span class="token punctuation">.</span><span class="token function">apply</span><span class="token punctuation">(</span>self<span class="token punctuation">,</span> params<span class="token punctuation">)</span><span class="token punctuation">;</span>
    186. 

  186. <span class="token punctuation">}</span>
    187. 

  187. 

  188. <span class="token comment">// acceptable</span>
    189. 

  189. <span class="token keyword">const</span> boundMethod <span class="token operator">=</span> <span class="token function">method</span><span class="token punctuation">.</span><span class="token function">bind</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    190. 

  190. 

  191. <span class="token comment">// best</span>
    192. 

  192. <span class="token keyword">const</span> <span class="token function-variable function">boundMethod</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter"><span class="token operator">...</span>params</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token function">method</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> params<span class="token punctuation">)</span><span class="token punctuation">;</span>
    193. 

  193. </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>简单的、单行的、不会复用的函数，建议采用箭头函数。<strong>如果函数体较为复杂，行数较多，还是应该采用传统的函数写法。</strong></p> <p><strong>所有配置项都应该集中在一个对象，放在最后一个参数，布尔值不可以直接作为参数</strong>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    194. 

  194. <span class="token keyword">function</span> <span class="token function">divide</span><span class="token punctuation">(</span><span class="token parameter">a<span class="token punctuation">,</span> b<span class="token punctuation">,</span> option <span class="token operator">=</span> <span class="token boolean">false</span></span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
    195. 

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

  196. 

  197. <span class="token comment">// good</span>
    198. 

  198. <span class="token keyword">function</span> <span class="token function">divide</span><span class="token punctuation">(</span><span class="token parameter">a<span class="token punctuation">,</span> b<span class="token punctuation">,</span> <span class="token punctuation">{</span> option <span class="token operator">=</span> <span class="token boolean">false</span> <span class="token punctuation">}</span> <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    199. 

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

  200. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>不要在函数体内使用 arguments 变量，使用 rest 运算符（...）代替。因为 rest 运算符显式表明你想要获取参数，而且 arguments 是一个类似数组的对象，而 rest 运算符可以提供一个真正的数组。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    201. 

  201. <span class="token keyword">function</span> <span class="token function">concatenateAll</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    202. 

  202.   <span class="token keyword">const</span> args <span class="token operator">=</span> <span class="token class-name">Array</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">.</span><span class="token function">call</span><span class="token punctuation">(</span>arguments<span class="token punctuation">)</span><span class="token punctuation">;</span>
    203. 

  203.   <span class="token keyword">return</span> args<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token string">''</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    204. 

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

  205. 

  206. <span class="token comment">// good</span>
    207. 

  207. <span class="token keyword">function</span> <span class="token function">concatenateAll</span><span class="token punctuation">(</span><span class="token parameter"><span class="token operator">...</span>args</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    208. 

  208.   <span class="token keyword">return</span> args<span class="token punctuation">.</span><span class="token function">join</span><span class="token punctuation">(</span><span class="token string">''</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    209. 

  209. <span class="token punctuation">}</span>
    210. 

  210. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><p>使用默认值语法设置函数参数的默认值。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    211. 

  211. <span class="token keyword">function</span> <span class="token function">handleThings</span><span class="token punctuation">(</span><span class="token parameter">opts</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    212. 

  212.   opts <span class="token operator">=</span> opts <span class="token operator">||</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
    213. 

  213. <span class="token punctuation">}</span>
    214. 

  214. 

  215. <span class="token comment">// good</span>
    216. 

  216. <span class="token keyword">function</span> <span class="token function">handleThings</span><span class="token punctuation">(</span><span class="token parameter">opts <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token punctuation">}</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    217. 

  217.   <span class="token comment">// ...</span>
    218. 

  218. <span class="token punctuation">}</span>
    219. 

  219. </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><h2 id="map-结构"><a href="#map-结构" class="header-anchor">#</a> Map 结构</h2> <p>注意区分 Object 和 Map，只有模拟现实世界的实体对象时，才使用 Object。如果只是需要<code>key: value</code>的数据结构，使用 Map 结构。因为 Map 有内建的遍历机制。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">let</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Map</span><span class="token punctuation">(</span>arr<span class="token punctuation">)</span><span class="token punctuation">;</span>
    220. 

  220. 

  221. <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> key <span class="token keyword">of</span> map<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    222. 

  222.   console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span><span class="token punctuation">;</span>
    223. 

  223. <span class="token punctuation">}</span>
    224. 

  224. 

  225. <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> value <span class="token keyword">of</span> map<span class="token punctuation">.</span><span class="token function">values</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    226. 

  226.   console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span>value<span class="token punctuation">)</span><span class="token punctuation">;</span>
    227. 

  227. <span class="token punctuation">}</span>
    228. 

  228. 

  229. <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> item <span class="token keyword">of</span> map<span class="token punctuation">.</span><span class="token function">entries</span><span class="token punctuation">(</span><span class="token punctuation">)</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>item<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">,</span> item<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    231. 

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

  232. </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><h2 id="class"><a href="#class" class="header-anchor">#</a> Class</h2> <p>总是用 Class，取代需要 prototype 的操作。因为 Class 的写法更简洁，更易于理解。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    233. 

  233. <span class="token keyword">function</span> <span class="token function">Queue</span><span class="token punctuation">(</span><span class="token parameter">contents <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    234. 

  234.   <span class="token keyword">this</span><span class="token punctuation">.</span>_queue <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token operator">...</span>contents<span class="token punctuation">]</span><span class="token punctuation">;</span>
    235. 

  235. <span class="token punctuation">}</span>
    236. 

  236. <span class="token class-name">Queue</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function-variable function">pop</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>
    237. 

  237.   <span class="token keyword">const</span> value <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>_queue<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    238. 

  238.   <span class="token keyword">this</span><span class="token punctuation">.</span>_queue<span class="token punctuation">.</span><span class="token function">splice</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    239. 

  239.   <span class="token keyword">return</span> value<span class="token punctuation">;</span>
    240. 

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

  241. 

  242. <span class="token comment">// good</span>
    243. 

  243. <span class="token keyword">class</span> <span class="token class-name">Queue</span> <span class="token punctuation">{</span>
    244. 

  244.   <span class="token function">constructor</span><span class="token punctuation">(</span><span class="token parameter">contents <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token punctuation">]</span></span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    245. 

  245.     <span class="token keyword">this</span><span class="token punctuation">.</span>_queue <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token operator">...</span>contents<span class="token punctuation">]</span><span class="token punctuation">;</span>
    246. 

  246.   <span class="token punctuation">}</span>
    247. 

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

  248.     <span class="token keyword">const</span> value <span class="token operator">=</span> <span class="token keyword">this</span><span class="token punctuation">.</span>_queue<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    249. 

  249.     <span class="token keyword">this</span><span class="token punctuation">.</span>_queue<span class="token punctuation">.</span><span class="token function">splice</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    250. 

  250.     <span class="token keyword">return</span> value<span class="token punctuation">;</span>
    251. 

  251.   <span class="token punctuation">}</span>
    252. 

  252. <span class="token punctuation">}</span>
    253. 

  253. </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>使用<code>extends</code>实现继承，因为这样更简单，不会有破坏<code>instanceof</code>运算的危险。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    254. 

  254. <span class="token keyword">const</span> inherits <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">'inherits'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    255. 

  255. <span class="token keyword">function</span> <span class="token function">PeekableQueue</span><span class="token punctuation">(</span><span class="token parameter">contents</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    256. 

  256.   <span class="token function">Queue</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> contents<span class="token punctuation">)</span><span class="token punctuation">;</span>
    257. 

  257. <span class="token punctuation">}</span>
    258. 

  258. <span class="token function">inherits</span><span class="token punctuation">(</span>PeekableQueue<span class="token punctuation">,</span> Queue<span class="token punctuation">)</span><span class="token punctuation">;</span>
    259. 

  259. <span class="token class-name">PeekableQueue</span><span class="token punctuation">.</span>prototype<span class="token punctuation">.</span><span class="token function-variable function">peek</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>
    260. 

  260.   <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>_queue<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    261. 

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

  262. 

  263. <span class="token comment">// good</span>
    264. 

  264. <span class="token keyword">class</span> <span class="token class-name">PeekableQueue</span> <span class="token keyword">extends</span> <span class="token class-name">Queue</span> <span class="token punctuation">{</span>
    265. 

  265.   <span class="token function">peek</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    266. 

  266.     <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>_queue<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
    267. 

  267.   <span class="token punctuation">}</span>
    268. 

  268. <span class="token punctuation">}</span>
    269. 

  269. </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="模块"><a href="#模块" class="header-anchor">#</a> 模块</h2> <p>首先，Module 语法是 JavaScript 模块的标准写法，坚持使用这种写法。使用<code>import</code>取代<code>require</code>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    270. 

  270. <span class="token keyword">const</span> moduleA <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">'moduleA'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    271. 

  271. <span class="token keyword">const</span> func1 <span class="token operator">=</span> moduleA<span class="token punctuation">.</span>func1<span class="token punctuation">;</span>
    272. 

  272. <span class="token keyword">const</span> func2 <span class="token operator">=</span> moduleA<span class="token punctuation">.</span>func2<span class="token punctuation">;</span>
    273. 

  273. 

  274. <span class="token comment">// good</span>
    275. 

  275. <span class="token keyword">import</span> <span class="token punctuation">{</span> func1<span class="token punctuation">,</span> func2 <span class="token punctuation">}</span> <span class="token keyword">from</span> <span class="token string">'moduleA'</span><span class="token punctuation">;</span>
    276. 

  276. </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>使用<code>export</code>取代<code>module.exports</code>。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// commonJS的写法</span>
    277. 

  277. <span class="token keyword">var</span> React <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">'react'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    278. 

  278. 

  279. <span class="token keyword">var</span> Breadcrumbs <span class="token operator">=</span> React<span class="token punctuation">.</span><span class="token function">createClass</span><span class="token punctuation">(</span><span class="token punctuation">{</span>
    280. 

  280.   <span class="token function">render</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    281. 

  281.     <span class="token keyword">return</span> <span class="token operator">&lt;</span>nav <span class="token operator">/</span><span class="token operator">&gt;</span><span class="token punctuation">;</span>
    282. 

  282.   <span class="token punctuation">}</span>
    283. 

  283. <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    284. 

  284. 

  285. module<span class="token punctuation">.</span>exports <span class="token operator">=</span> Breadcrumbs<span class="token punctuation">;</span>
    286. 

  286. 

  287. <span class="token comment">// ES6的写法</span>
    288. 

  288. <span class="token keyword">import</span> React <span class="token keyword">from</span> <span class="token string">'react'</span><span class="token punctuation">;</span>
    289. 

  289. 

  290. <span class="token keyword">class</span> <span class="token class-name">Breadcrumbs</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>
    291. 

  291.   <span class="token function">render</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    292. 

  292.     <span class="token keyword">return</span> <span class="token operator">&lt;</span>nav <span class="token operator">/</span><span class="token operator">&gt;</span><span class="token punctuation">;</span>
    293. 

  293.   <span class="token punctuation">}</span>
    294. 

  294. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    295. 

  295. 

  296. <span class="token keyword">export</span> <span class="token keyword">default</span> Breadcrumbs<span class="token punctuation">;</span>
    297. 

  297. </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>如果模块只有一个输出值，就使用<code>export default</code>，如果模块有多个输出值，就不使用<code>export default</code>，<code>export default</code>与普通的<code>export</code>不要同时使用。</p> <p>不要在模块输入中使用通配符。因为这样可以确保你的模块之中，有一个默认输出（export default）。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token comment">// bad</span>
    298. 

  298. <span class="token keyword">import</span> <span class="token operator">*</span> <span class="token keyword">as</span> myObject <span class="token keyword">from</span> <span class="token string">'./importModule'</span><span class="token punctuation">;</span>
    299. 

  299. 

  300. <span class="token comment">// good</span>
    301. 

  301. <span class="token keyword">import</span> myObject <span class="token keyword">from</span> <span class="token string">'./importModule'</span><span class="token punctuation">;</span>
    302. 

  302. </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>如果模块默认输出一个函数，函数名的首字母应该小写。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">function</span> <span class="token function">makeStyleGuide</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    303. 

  303. <span class="token punctuation">}</span>
    304. 

  304. 

  305. <span class="token keyword">export</span> <span class="token keyword">default</span> makeStyleGuide<span class="token punctuation">;</span>
    306. 

  306. </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>如果模块默认输出一个对象，对象名的首字母应该大写。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">const</span> StyleGuide <span class="token operator">=</span> <span class="token punctuation">{</span>
    307. 

  307.   <span class="token literal-property property">es6</span><span class="token operator">:</span> <span class="token punctuation">{</span>
    308. 

  308.   <span class="token punctuation">}</span>
    309. 

  309. <span class="token punctuation">}</span><span class="token punctuation">;</span>
    310. 

  310. 

  311. <span class="token keyword">export</span> <span class="token keyword">default</span> StyleGuide<span class="token punctuation">;</span>
    312. 

  312. </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><h2 id="eslint-的使用"><a href="#eslint-的使用" class="header-anchor">#</a> ESLint 的使用</h2> <p>ESLint 是一个语法规则和代码风格的检查工具，可以用来保证写出语法正确、风格统一的代码。</p> <p>首先，安装 ESLint。</p> <div class="language-bash line-numbers-mode"><pre class="language-bash"><code>$ <span class="token function">npm</span> i <span class="token parameter variable">-g</span> eslint
    313. 

  313. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><p>然后，安装 Airbnb 语法规则，以及 import、a11y、react 插件。</p> <div class="language-bash line-numbers-mode"><pre class="language-bash"><code>$ <span class="token function">npm</span> i <span class="token parameter variable">-g</span> eslint-config-airbnb
    314. 

  314. $ <span class="token function">npm</span> i <span class="token parameter variable">-g</span> eslint-plugin-import eslint-plugin-jsx-a11y eslint-plugin-react
    315. 

  315. </code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>最后，在项目的根目录下新建一个<code>.eslintrc</code>文件，配置 ESLint。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token punctuation">{</span>
    316. 

  316.   <span class="token string-property property">&quot;extends&quot;</span><span class="token operator">:</span> <span class="token string">&quot;eslint-config-airbnb&quot;</span>
    317. 

  317. <span class="token punctuation">}</span>
    318. 

  318. </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>现在就可以检查，当前项目的代码是否符合预设的规则。</p> <p><code>index.js</code>文件的代码如下。</p> <div class="language-javascript line-numbers-mode"><pre class="language-javascript"><code><span class="token keyword">var</span> unusued <span class="token operator">=</span> <span class="token string">'I have no purpose!'</span><span class="token punctuation">;</span>
    319. 

  319. 

  320. <span class="token keyword">function</span> <span class="token function">greet</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    321. 

  321.     <span class="token keyword">var</span> message <span class="token operator">=</span> <span class="token string">'Hello, World!'</span><span class="token punctuation">;</span>
    322. 

  322.     <span class="token function">alert</span><span class="token punctuation">(</span>message<span class="token punctuation">)</span><span class="token punctuation">;</span>
    323. 

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

  324. 

  325. <span class="token function">greet</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    326. 

  326. </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>使用 ESLint 检查这个文件，就会报出错误。</p> <div class="language-bash line-numbers-mode"><pre class="language-bash"><code>$ eslint index.js
    327. 

  327. index.js
    328. 

  328.   <span class="token number">1</span>:1  error  Unexpected var, use <span class="token builtin class-name">let</span> or const instead          no-var
    329. 

  329.   <span class="token number">1</span>:5  error  unusued is defined but never used                 no-unused-vars
    330. 

  330.   <span class="token number">4</span>:5  error  Expected indentation of <span class="token number">2</span> characters but found <span class="token number">4</span>  indent
    331. 

  331.   <span class="token number">4</span>:5  error  Unexpected var, use <span class="token builtin class-name">let</span> or const instead          no-var
    332. 

  332.   <span class="token number">5</span>:5  error  Expected indentation of <span class="token number">2</span> characters but found <span class="token number">4</span>  indent
    333. 

  333. 

  334. ✖ <span class="token number">5</span> problems <span class="token punctuation">(</span><span class="token number">5</span> errors, <span class="token number">0</span> warnings<span class="token punctuation">)</span>
    335. 

  335. </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>上面代码说明，原文件有五个错误，其中两个是不应该使用<code>var</code>命令，而要使用<code>let</code>或<code>const</code>；一个是定义了变量，却没有使用；另外两个是行首缩进为 4 个空格，而不是规定的 2 个空格。</p></div></div>  <div class="page-edit"><div class="edit-link"><a href="https://github.com/heBody/blog/edit/master/docs/《ES6 教程》笔记/25.编程风格.md" target="_blank" rel="noopener noreferrer">编辑</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <div class="tags"><a href="/blog/tags/?tag=ES6" title="标签">#ES6</a></div> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2022/12/14, 19:36:42</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/blog/pages/a79ca2e64ceae213/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">Module 的加载实现</div></a> <a href="/blog/pages/32c35f7651d6e58e/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">读懂 ECMAScript 规格</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
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