45个实用的JavaScript技巧、窍门和最佳实践

骑猪看日落 2022-09-22 11:53 182阅读 0赞

如你所知，JavaScript是世界上第一的编程语言，它是Web的语言，是移动混合应用（mobile hybrid apps）的语言（比如[PhoneGap][]或者[Appcelerator][]），是服务器端的语言（比如[NodeJS][]或者[Wakanda][]），并且拥有很多其他的实现。同时它也是很多新手的启蒙语言，因为它不但可以在浏览器上显示一个简单的alert信息，而且还可以用来控制一个机器人（使用[nodebot][]，或者[nodruino][]）。掌握JavaScript并且能够写出组织规范并性能高效的代码的开发人员，已经成为人才市场上的猎寻对象。

![keep-calm-and-learn-javascript][]

在这篇文章中，我将分享一组JavaScript的技巧、窍门和最佳实践，这些都是JavaScript程序员应该知晓的，不管他们是使用在浏览器/引擎上，还是服务器端（SSJS——Service Side JavaScript）JavaScript解释器上。

【译者注：原文作者总共写了44条（漏写了第3条），译者自己补了一条觉得比较重要的技巧。】

需要注意的是，这篇文章中的代码片段都在最新的Google Chrome（版本号30）上测试过，它使用V8 JavaScript引擎（V8 3.20.17.15）

1 – 在第一次给一个变量赋值的时候不要忘记使用`var`关键字

给一个未定义的变量赋值会导致创建一个全局变量。要避免全局变量。

2 – 使用===，而不是＝＝

==（或!=）操作符在需要的时候会自动执行类型转换。===（或!==）操作不会执行任何转换。它将比较值和类型，而且在速度上也被认为优于==。

3 – 使用闭包实现私有变量（译者添加）

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  </tr> 
 </tbody> 
</table>

4 – 在语句结尾处使用分号

在语句结尾处使用分号是一个很好的实践。如果你忘记写了你也不会被警告，因为多数情况下JavaScript解释器会帮你加上分号。

5 – 创建对象的构造函数

6 – 小心使用typeof、instanceof和constructor

7 – 创建一个自调用函数（Self-calling Funtion）

这个经常被称为自调用匿名函数（Self-Invoked Anonymous Function）或者即时调用函数表达式（IIFE-Immediately Invoked Function Expression)。这是一个在创建后立即自动执行的函数，通常如下：

8- 从数组中获取一个随机项

9 – 在特定范围内获取一个随机数

这个代码片段在你想要生成测试数据的时候非常有用，比如一个在最小最大值之间的一个随机薪水值。

10 – 在0和设定的最大值之间生成一个数字数组

11 – 生成一个随机的数字字母字符串

【译者注：特意查了一下Math.random()生成0到1之间的随机数，number.toString(36)是将这个数字转换成36进制（0-9，a-z），最后substr去掉前面的“0.”字符串】

12 – 打乱一个数字数组

13 – String的trim函数

在Java、C\#、PHP和很多其他语言中都有一个经典的 trim 函数，用来去除字符串中的空格符，而在JavaScript中并没有，所以我们需要在String对象上加上这个函数。

【译者注：去掉字符串的前后空格，不包括字符串内部空格】

14 – 附加（append）一个数组到另一个数组上

【译者注：其实concat可以直接实现两个数组的连接，但是它的返回值是一个新的数组。这里是直接改变array1】

15 – 将arguments对象转换成一个数组

【译者注：[arguments对象是一个类数组对象，但不是一个真正的数组][arguments]】

16 – 验证参数是否是数字（number）

17 – 验证参数是否是数组

注意：如果toString()方法被重写了（overridden），你使用这个技巧就不能得到想要的结果了。或者你可以使用：

如果你不在使用多重frames的情况下，你还可以使用 instanceof 方法。但如果你有多个上下文，你就会得到错误的结果。

【译者注：关于如何判断数组网上有不少讨论，大家可以google一下。[这篇][Link 1]就写的挺详细的。】

18 – 获取一个数字数组中的最大值或最小值

【译者注：这里使用了Function.prototype.apply方法传递参数的技巧】

19 – 清空一个数组

20 – 不要使用 delete 来删除一个数组中的项。

使用 splice 而不要使用 delete 来删除数组中的某个项。使用 delete 只是用 undefined 来替换掉原有的项，并不是真正的从数组中删除。

不要使用这种方式：

而使用：

delete 方法应该被用来删除一个对象的某个属性。

21 – 使用 length 来截短一个数组

跟上面的清空数组的方式类似，我们使用 length 属性来截短一个数组。

此外，如果你将一个数组的 length 设置成一个比现在大的值，那么这个数组的长度就会被改变，会增加新的 undefined 的项补上。 数组的 length 不是一个只读属性。

22 – 使用逻辑 AND/OR 做条件判断

逻辑 AND 还可以被使用来为函数参数设置默认值

23 – 使用 map() 方法来遍历一个数组里的项

24 – 四舍五入一个数字，保留N位小数

25 – 浮点数问题

为什么会这样？ 0.1+0.2等于0.30000000000000004。你要知道，所有的JavaScript数字在内部都是以64位二进制表示的浮点数，符合IEEE 754标准。更多的介绍，可以阅读[这篇博文][Link 2]。你可以使用 toFixed() 和 toPrecision() 方法解决这个问题。

26 – 使用for-in遍历一个对象内部属性的时候注意检查属性

下面的代码片段能够避免在遍历一个对象属性的时候访问原型的属性

27 – 逗号操作符

28 – 缓存需要计算和查询（calculation or querying）的变量

对于jQuery选择器，我们最好缓存这些DOM元素。

29 – 在调用 isFinite()之前验证参数

30 – 避免数组中的负数索引（negative indexes）

确保调用 indexOf 时的参数不是负数。

31 – 基于JSON的序列化和反序列化（serialization and deserialization）

32 – 避免使用 eval() 和 Function 构造函数

使用 eval 和 Function 构造函数是非常昂贵的操作，因为每次他们都会调用脚本引擎将源代码转换成可执行代码。

33 – 避免使用 with()

使用 with() 会插入一个全局变量。因此，同名的变量会被覆盖值而引起不必要的麻烦。

34 – 避免使用 for-in 来遍历一个数组

避免使用这样的方式：

更好的方式是：

附加的好处是，i 和 len 两个变量的取值都只执行了一次，会比下面的方式更高效：

为什么？因为arrayNumbers.length每次循环的时候都会被计算。

35 – 在调用 setTimeout() 和 setInterval() 的时候传入函数，而不是字符串。

如果你将字符串传递给 setTimeout() 或者 setInterval()，这个字符串将被如使用 eval 一样被解析，这个是非常耗时的。  
不要使用：

而用：

36 – 使用 switch/case 语句，而不是一长串的 if/else

在判断情况大于2种的时候，使用 switch/case 更高效，而且更优雅（更易于组织代码）。但在判断的情况超过10种的时候不要使用 switch/case。  
【译者注：查了一下文献，大家可以看一下[这篇介绍][Link 3]】

37 – 在判断数值范围时使用 switch/case

在下面的这种情况，使用 switch/case 判断数值范围的时候是合理的：

<table style="margin-left: 0px; font-size: 13px; border: none !important; margin-top: 0px !important; margin-right: 0px !important; margin-bottom: 0px !important; padding: 0px !important; border-collapse: collapse !important; border-spacing: 0px !important; width: auto !important; table-layout: auto !important; background: none !important;"> 
 <tbody style="border: 0px; margin: 0px; padding: 0px;"> 
  <tr style="border: none !important; margin: 0px !important; padding: 0px !important; vertical-align: top !important; background: none;"> 
   <td style="font-size: 13px; text-align: center; border: none !important; margin: 0px !important; padding: 0px !important; vertical-align: top !important; font-family: Monaco, MonacoRegular, 'Courier New', monospace !important; background-image: none; background-attachment: initial; background-color: rgb(238, 238, 238) !important; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"> 
    <div style="border: none; margin: 0px; padding-right: 0px; padding-left: 0px; text-align: left; white-space: nowrap; padding-top: 5px !important; padding-bottom: 3px !important; line-height: 15px !important; background: none;"> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       1 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       2 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       3 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       4 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       5 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       6 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       7 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       8 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       9 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       10 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       11 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       12 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       13 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       14 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       15 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       16 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       17 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       18 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       19 
     </div> 
    </div></td> 
   <td style="font-size: 13px; text-align: center; width: 581px; border: none !important; margin: 0px !important; padding: 0px !important; vertical-align: top !important; font-family: Monaco, MonacoRegular, 'Courier New', monospace !important; background: none;"> 
    <div style="margin: 0px; padding-right: 0px; padding-left: 0px; text-align: left; white-space: pre; overflow: visible; tab-size: 4; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; line-height: 15px !important; background: none !important;"> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: bold !important; color: rgb(128, 0, 128) !important;">function</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">getCategory</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">age</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">{ </span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: bold !important; color: rgb(128, 0, 128) !important;">var</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">category</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">=</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">switch</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: bold !important; color: rgb(128, 0, 128) !important;">true</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">{ </span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">case</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">isNaN</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">age</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">:</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">category</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">=</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">not</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">an </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">age</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
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     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">break</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
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     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">case</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">age</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">gt</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">=</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">50</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">:</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">category</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">=</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">Old</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">break</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">case</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">age</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">lt</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">=</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">20</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">:</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">category</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">=</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">Baby</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">break</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">default</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">:</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">category</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">=</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">Young</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">break</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
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     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">}</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">return</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">category</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
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     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">}</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">getCategory</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">5</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&nbsp;&nbsp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(153, 153, 153) !important; font-style: italic !important;">// will return &amp;quot;Baby&amp;quot;</span> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

【译者注：一般对于数值范围的判断，用 if/else 会比较合适。 switch/case 更适合对确定数值的判断】

38 – 为创建的对象指定prototype对象

写一个函数来创建一个以指定参数作为prototype的对象是有可能：

39 – 一个HTML转义函数

<table style="margin-left: 0px; font-size: 13px; border: none !important; margin-top: 0px !important; margin-right: 0px !important; margin-bottom: 0px !important; padding: 0px !important; border-collapse: collapse !important; border-spacing: 0px !important; width: auto !important; table-layout: auto !important; background: none !important;"> 
 <tbody style="border: 0px; margin: 0px; padding: 0px;"> 
  <tr style="border: none !important; margin: 0px !important; padding: 0px !important; vertical-align: top !important; background: none;"> 
   <td style="font-size: 13px; text-align: center; border: none !important; margin: 0px !important; padding: 0px !important; vertical-align: top !important; font-family: Monaco, MonacoRegular, 'Courier New', monospace !important; background-image: none; background-attachment: initial; background-color: rgb(238, 238, 238) !important; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;"> 
    <div style="border: none; margin: 0px; padding-right: 0px; padding-left: 0px; text-align: left; white-space: nowrap; padding-top: 5px !important; padding-bottom: 3px !important; line-height: 15px !important; background: none;"> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       1 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       2 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       3 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       4 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       5 
     </div> 
     <div style="border-right-width: 1px !important; border-top-style: none; border-right-style: solid !important; border-bottom-style: none; border-left-style: none; border-right-color: rgb(222, 222, 222) !important; margin: 0px; padding: 0px 5px; font-size: inherit !important; font-family: inherit; text-align: right !important; height: inherit; line-height: inherit !important; font-weight: inherit !important; min-width: 1.2em !important; color: rgb(170, 170, 170) !important; background: none;">
       6 
     </div> 
    </div></td> 
   <td style="font-size: 13px; text-align: center; width: 1397px; border: none !important; margin: 0px !important; padding: 0px !important; vertical-align: top !important; font-family: Monaco, MonacoRegular, 'Courier New', monospace !important; background: none;"> 
    <div style="margin: 0px; padding-right: 0px; padding-left: 0px; text-align: left; white-space: pre; overflow: visible; tab-size: 4; border: none !important; padding-top: 5px !important; padding-bottom: 3px !important; line-height: 15px !important; background: none !important;"> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: bold !important; color: rgb(128, 0, 128) !important;">function</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">escapeHTML</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">{ </span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: bold !important; color: rgb(128, 0, 128) !important;">var</span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">replacements</span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">{ </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">lt</span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">:</span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">quot</span> 
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     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

40 – 避免在循环内部使用 try-catch-finally

在运行时，每次当 catch 从句被执行的时候，被捕获的异常对象会赋值给一个变量，而在 try-catch-finally 结构中，每次都会新建这个变量。

避免这样的写法：

而使用：

41 – 为 XMLHttpRequests 设置超时。

在一个XHR请求占用很长时间后（比如由于网络问题），你可能需要中止这次请求，那么你可以对XHR调用配套使用 setTimeout()。

此外，一般你应该完全避免同步的Ajax请求。

42 – 处理WebSocket超时

通常，在一个WebSocket连接创建之后，如果你没有活动的话，服务器会在30秒之后断开（time out）你的连接。防火墙也会在一段时间不活动之后断开连接。

为了防止超时的问题，你可能需要间歇性地向服务器端发送空消息。要这样做的话，你可以在你的代码里添加下面的两个函数：一个用来保持连接，另一个用来取消连接的保持。通过这个技巧，你可以控制超时的问题。

使用一个 timerID：

keepAlive()方法应该被添加在webSOcket连接的 onOpen() 方法的最后，而 cancelKeepAlive() 添加在 onClose() 方法的最后。

43 – 牢记，[原始运算符始终比函数调用要高效][Link 4]。使用[VanillaJS][]。

举例来说，不使用：

而用：

44 – 编码的时候不要忘记使用代码整洁工具。在上线之前使用JSLint和代码压缩工具（minification）（比如JSMin）。《[省时利器：代码美化与格式化工具][Link 5]》

45 – JavaScript是不可思议的。[最好的JavaScript学习资源][JavaScript]。

# 总结 #

我知道还有很多其他的技巧，窍门和最佳实践，所以如果你有其他想要添加或者对我分享的这些有反馈或者纠正，请在评论中指出。

# 引用 #

在这篇文章中，我使用了一些我自己的代码片段，也有一些代码片段来自别人的文章或者论坛：

*  [JavaScript Performance Best Practices][] ([CC][])
 *  [Google Code JavaScript tips][]
 *  [StackOverFlow tips and tricks][]
 *  [TimeOut for XHR][]

[PhoneGap]: http://phonegap.com/
[Appcelerator]: http://www.appcelerator.com/
[NodeJS]: http://nodejs.org/
[Wakanda]: http://wakanda.org/
[nodebot]: http://nodebots.io/
[nodruino]: http://semu.github.io/noduino/
[keep-calm-and-learn-javascript]: /images/20220721/40a3704461c44a27994bfcb898c356b0.png
[arguments]: http://debuggable.com/posts/turning-javascript-s-arguments-object-into-an-array:4ac50ef8-3bd0-4a2d-8c2e-535ccbdd56cb
[Link 1]: http://perfectionkills.com/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/
[Link 2]: http://www.2ality.com/2012/04/number-encoding.html
[Link 3]: http://oreilly.com/server-administration/excerpts/even-faster-websites/writing-efficient-javascript.html#the_fastest_conditionals
[Link 4]: http://dev.opera.com/articles/view/efficient-javascript/?page=2#primitiveoperator
[VanillaJS]: http://vanilla-js.com/
[Link 5]: http://blog.jobbole.com/16979/
[JavaScript]: http://stackoverflow.com/questions/11246/best-resources-to-learn-javascript
[JavaScript Performance Best Practices]: http://developer.nokia.com/Community/Wiki/JavaScript_Performance_Best_Practices
[CC]: http://creativecommons.org/licenses/by-nc-sa/2.5/
[Google Code JavaScript tips]: https://code.google.com/p/jslibs/wiki/JavascriptTips
[StackOverFlow tips and tricks]: http://stackoverflow.com/questions/724826/javascript-tips-and-tricks-javascript-best-practices
[TimeOut for XHR]: http://stackoverflow.com/questions/6888409/settimeout-for-xhr-requests