1. 最笨的办法.......

function get() {    

　　var s = 22.127456 + "";

    var str = s.substring(0,s.indexOf(".") + 3);

    alert(str); }

2. 正则 效果不错

<script type="text/javascript">

　　onload = function(){    

　　var a = "23.456322";    

　　var aNew;    

　　var re = /([0-9]+\.[0-9]{2})[0-9]*/;

    aNew = a.replace(re,"$1");

     alert(aNew); }

</script>

3. 他就比较聪明了.....

<script> var num=22.127456; alert( Math.round(num*100)/100); </script>

4.会用新鲜东西的朋友.......

 <script> var num=22.127456; alert( num.toFixed(2)); </script>