简单的正则表达式
验证四位数字，若是4位数字，则弹出true，否则，弹出false。
<html>
<head>
<title>用户验证</title>
<script type="text/javascript">
function save(){
var strvar = document.getElementById('input_id').value;
//var reg = (/^(V?\d{4}_)/);
var reg = (/^(\d{4})$/);
//var reg = (/^(\d{1,4})(-|\/)(\d{1,2})\2(\d{1,2})$/);
if(reg.test(strvar)){
alert(reg.test(strvar));
}else{
alert(reg.test(strvar));
}
}
//var reg = /^(V?\d{4})*$/;
//return reg.test(str);
</script>
</head>
<body>
<input type="test" name="Email" id="input_id" onchange="save()">
</body>
</html>