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