困扰了很长一段时间的Javascript的一个BUG

原文：http://blog.csdn.net/yycai/archive/2009/01/12/3760366.aspx

 

 

问了好多人，都没有得到一个满意的答复，终于忍不住在TopLanguage提问了一下，呵呵，终于有高人回复了，原来是一个bug：

http://code.google.com/p/chromium/issues/detail?id=2161

https://bugzilla.mozilla.org/show_bug.cgi?id=98409#c35

 

摘录如下：

Looking at the reduced test case, there is a regular expression literal on line 5.  
According to the spec, there is only one instance of a regular expression literal 
(ECMA 262 7.8.5), which is created when the literal is scanned.  So each time jsfGetFormDate is called, a new RegExp object is not created.  Instead the same 
RegExp object is reused over and over again.

Since the 'g' flag is specified, that means that the global property is true for the 
RegExp object (ECMA 262 15.10.4.1).  In the case where the global property is true, 
when exec successfully finds a match, the lastIndex property of the RegExp is set to one plus the index of the last input character matched so far (ECMA 262 15.10.2.1, 
15.10.6.2 step 11).  So in this case lastIndex is 10 after the first call to jsfGetFormDate, since the length of the input string is 10 and the complete string is 
matched.

Remember that there is only one instance of the regular expression literal RegExp 
object, so the next time jsfGetFormDate is called, the lastIndex property of the 
RegExp object is still 10.  So the next time exec is called, it attempts to match 
starting at index 10 of the input string (ECMA 262 15.10.6.2 step 7).  Since the 
input string is only 10 characters in length, no match is found.  Then it tries again 
starting at index 11 (ECMA 262 15.10.6.2 steps 8 and 9) and, because 11 is greater 
than the length of the input string (which is 10), it fails and returns null (ECMA 
262 15.10.6.2 step 6).

----------------------------------------

Potential workarounds:

1. Do not specify the global 'g' flag in the regular expression.

2. Instead of using a regular expression literal, instead use something like this:

     var p = '(0?//d{1,2})[///-]0?//d{1,2}[///-]//d{4}';
     var re = new RegExp(p, 'g');

   which will create a new RegExp object each time.



当然你也可以在每次使用之前把它的lastIndex属性设为0～～