function ajax(url,fn)
{
 var xmlhttp;
 url=url+"&sid="+Math.random(); 
 
 if (window.XMLHttpRequest) xmlhttp=new XMLHttpRequest();
 else if (window.ActiveXObject) xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
 else alert("Your browser does not support XMLHTTP!");
 
 xmlhttp.onreadystatechange=function()
 { 
  if(xmlhttp.readyState==4) fn(xmlhttp.responseText);  
 }

 xmlhttp.open("GET",url,true);
 xmlhttp.send(null); 
}