JS converts numbers into three-digit comma-separated styles (sample code)

Copy the code code as follows:

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;

}