Javascript Tips (Updating...)

一时失言乱红尘 2021-11-10 13:04 198阅读 0赞

1.判断一个object的类型

if ((typeof o == "object") && (o.constructor == Date))
        // Then do something with the Date object...
       if ((typeof o == "object") && (o instanceof Date))
        // Then do something with the Date object...

<table> 
 <thead> 
  <tr> 
   <th>Variable</th> 
   <th>typeof Variable</th> 
   <th>Variable.constructor</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>{ an: “object” }</td> 
   <td>object</td> 
   <td>Object</td> 
  </tr> 
  <tr> 
   <td>[ “an”, “array” ]</td> 
   <td>object</td> 
   <td>Array</td> 
  </tr> 
  <tr> 
   <td>function(){}</td> 
   <td>function</td> 
   <td>Function</td> 
  </tr> 
  <tr> 
   <td>“a string”</td> 
   <td>string</td> 
   <td>String</td> 
  </tr> 
  <tr> 
   <td>55</td> 
   <td>number</td> 
   <td>Number</td> 
  </tr> 
  <tr> 
   <td>true</td> 
   <td>boolean</td> 
   <td>Boolean</td> 
  </tr> 
  <tr> 
   <td>new User()</td> 
   <td>object</td> 
   <td>User</td> 
  </tr> 
 </tbody> 
</table>

2. javascript中的字符串连接  
    众所周知在C\#中，StringBuilder的效率比String.Concat的效率要高几个数量级  
    具体参阅： [String.Concat versus Text.Stringbuilder][]  
    javascript里面也有同样问题，之前做了一个小测试，看看各浏览器的链接效率。  
     [Which browser is faster :<][Which browser is faster]   
    可以看出，在除了IE的浏览器内，都对Js的字符串连接操作做了优化。so在IE中做大量的字符串连接操作时，应该考虑下性能问题咯。

转载于:https://www.cnblogs.com/chnldw/archive/2007/04/11/709417.html

[String.Concat versus Text.Stringbuilder]: http://codebetter.com/blogs/raymond.lewallen/archive/2004/12/02/34739.aspx
[Which browser is faster]: http://www.cnblogs.com/chnldw/archive/2007/09/24/904362.html