<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title>Untitled Page</title>
<script src="http://code.jquery.com/jquery-1.11.1.min.js" type="text/javascript"></script>
</head>
<body>
<input id="txt_num" type="text" />
<input id="btn_submit" type="button" value="提交" />
<script type="text/javascript">
$(function () {
$("#btn_submit").click(function(){
var num = $("#txt_num").val();
if(!isNaN(num)){
var dot = num.indexOf(".");
if(dot != -1){
var dotCnt = num.substring(dot+1,num.length);
if(dotCnt.length > 2){
alert("小数位已超过2位！");
}
}
}else{
alert("数字不合法！");
}
});
});
</script>
</body>
</html>