自动为数字千位数，百万位数添加逗号

<script type="text/javascript">

//获得原数字
var countStr = document.getElementById("lblCount").innerText;
var countLength = countStr.length;
var str = "";
for (var i = 0; i < parseInt((countLength-1) / 3) ; i++) {
var j = 0;
if(countStr.indexOf(",")>-1)
{

//例：123456,789 index等于6

//这里等于从6开始继续，相当于为原来的9开始计算
j = countStr.length-countStr.indexOf(",");
//alert(j);
}
countStr = countStr.substring(0, countStr.length - 3 - j) + "," + countStr.substring(countStr.length - 3 - j, countStr.length);
}
document.getElementById("lblCount").innerText = countStr;

</script>

第二种：

function formatNumber(num){
if(!/^(+|-)?(d+)(.d+)?$/.test(num)){return num;}
var a = RegExp.$1, b = RegExp.$2, c = RegExp.$3;
var re = new RegExp().compile("(\d)(\d{3})(,|$)");
while(re.test(b)) b = b.replace(re,"$1,$2$3");
return a +""+ b +""+ c;
}