<body>
<p id="demo">123456789</p>
<button onclick="geshihua()">格式化数字</button>
<p id="demo3"></p>
</body>
<script src="http://libs.baidu.com/jquery/2.0.0/jquery.js"></script>
<script>
function geshihua(){
var dataval = parseInt($("#demo").text());
var data2 = dataval.toFixed(2).replace(/\d{1,3}(?=(\d{3})+(\.\d*)?$)/g,'$&,');
return $("#demo3").text(data2);
}
</script>