JS将数字转换成三位逗号分隔的样式

function formatNum(num)

{

if(!/^(\+|-)?(\d+)(\.\d+)?$/.test(num)){alert("wrong!"); 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;

}

来源：http://www.cnblogs.com/usea/archive/2009/03/12/1409709.html