检测八位数字是否为有效日期的正则

<html> 
<head> 
<title>测试八位数字是否为有效日期</title> 
</head> 
<script language="javascript"><!-- 
    /* 
        // Regex Example in JavaScript 
        // Rainsome Studio         
        // 2009-07-16 in Shanghai 
        //测试八位数字是否为有效日期 
    */     
    function fun1() 
    { 
        var str1=document.getElementById("str1").value; 
        var str2=document.getElementById("str2").value;     
        var regex1 = new RegExp(str2,'g'); 
        return regex1.test(str1);     
    } 
    function fun2(){alert(fun1());}

// --></script> 
<body> 
         
<span>String : </span><input id="str1" type="text" value="19990228" size="100"/> 
        
 
        <span>Regex : </span><input id="str2" type="text" 
            value='^(?:(?:(?:(?=\d{2}(?:(?:[02468][048])|(?:[13579][26])))\d{4}02(?!00)[0-2]\d))|(?:\d{4}(?:(?:(?:(?:0[469])|(?:11))(?!00)(?:(?:[0-2]\d)|(?:30)))|(?:(?:(?:0[13578])|(?:1[02]))(?!00)(?:(?:[0-2]\d)|(?:3[01])))|(?:02(?!(?:00)|(?:29))[0-2]\d))))$' 
            size="100"/> 
        
 
        <input type="button" value="OK" onclick="javascript:fun2();"/> 
         
</body> 
</html>

[Ctrl+A 全选注:如需引入外部Js需刷新才能执行]