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] Démarrage rapide de Node.js](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
