JavaScript 中的 RegExp 对象用于正则表达式相关的操作，这个对象提供了一个方法 test 来判定某个字符串是否满足某个 pattern. 返回值是 true/false.
今天我碰到了一个问题：
<script type=text/javascript>
<!--
var re = /^\d+(?:\.\d)?$/ig;
alert(re.test(112.3));
alert(re.test(33));
//-->
</script>
这里两个测试的字符串应该都满足正则表达式中的模式，返回 true. 可是测试结果却依次是：true, false.
我估计问题的原因可能是因为 RegExp 对象是有状态的，并且在 test 方法的执行时会在某个步骤中利用到状态信息，这样就造成了错误。
（注：RegExp 全局对象有一些静态属性和方法，比如 RegExp.$1... RegExp$9, 等）
解决这个问题的办法也很简单，就是每次重新初始化一次正则表达式对象：
<script type=text/javascript>
<!--
alert(/^\d+(?:\.\d)?$/ig.test(112.3));
alert(/^\d+(?:\.\d)?$/ig.test(33));
//-->
</script>
在我看来，JavaScript 中正则表达式的这个行为设计的很奇怪，应该说是和正常使用习惯有那么一点点的不同。虽然使用了很久的 JavaScript, 却一直没有注意到这个奇怪的现象。其他语言比如 Python, C# 等都不是这样的。
了解这个问题详细原因的朋友，请不吝指教。
posted on 2007-01-08 15:23 木野狐 阅读(330) 评论(1) 编辑 收藏 引用 网摘 所属分类: ASP,JS,CSS
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# re: 注意 JavaScript 中 RegExp 对象的 test 方法 2007-01-08 23:33 Derek
lastIndex Property See Also
RegExp Object Properties | Regular Expression Syntax
Applies To: RegExp Object
Requirements
Version 3
Returns the character position where the next match begins in a searched string.
RegExp.lastIndex
The object associated with this property is always the global RegExp object.
Remarks
The lastIndex property is zero-based, that is, the index of the first character is zero. Its initial value is –1. Its value is modified whenever a successful match is made.
The lastIndex property is modified by the exec and test methods of the RegExp object, and the match, replace, and split methods of the String object.
The following rules apply to values of lastIndex:
If there is no match, lastIndex is set to -1.
If lastIndex is greater than the length of the string, test and exec fail and lastIndex is set to -1.
If lastIndex is equal to the length of the string, the regular expression matches if the pattern matches the empty string. Otherwise, the match fails and lastIndex is reset to -1.
Otherwise, lastIndex is set to the next position following the most recent match.
http://www.cnblogs.com/RChen/archive/2007/01/08/regexp_test.html
