1    var x=12345678;
2    x=x.toString();
3    var lastThree = x.substring(x.length-3);
4    var otherNumbers = x.substring(0,x.length-3);
5    if(otherNumbers != '')
6        lastThree = ',' + lastThree;
7    var res = otherNumbers.replace(/\B(?=(\d{2})+(?!\d))/g, ",") + lastThree;
8    alert(res);