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;
}
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
