SOURCE

var arr = [];
function main(num){
  if(num==null) return;
  var n = parseInt(num).toString();
  s(n)
}
function s(num){
  if(num.length>3){
    arr[arr.length]=num.slice(-3);
    s(num.slice(0,-3));
  }else{
    arr[arr.length]=num;
  }
}
main(123456789)
document.write(arr.reverse().join(','))

<script>
var arr = [];
function main(num){
  if(num==null) return;
  var n = parsenInt(num).toString();
  s(n)
}
function s(num){
  if(num.length>3){
    arr[arr.length]=num.slice(-3);
    s(num.slice(0,-3));
  }else{
    arr[arr.length]=num;
  }
}
main(123456789)
document.write(arr.reverse().join(','))
</script>