setIntervall without multiply

setIntervall without multiply

I'm doing a chat using prepend() into a setInterval();

Code:
  1. setInterval(function(){
  2.       $.post("ajax/compartilhamentos.php",function(data){
  3.             $(".compartilhamentos").prepend(data);
  4.       });
  5. }, 5000);

the problem is that if something has already been loaded I do not want it to load again, and so just prepend new "data".

does anyone know how ?