var listenerClient;
if (window.XMLHttpRequest) { // Mozilla, Safari, ...
    listenerClient = new XMLHttpRequest();
} else if (window.ActiveXObject) { // IE
    listenerClient = new ActiveXObject("Microsoft.XMLHTTP");
}
listenerClient.onreadystatechange = listenerHandler;

function startListenerUpdate() {
  listenerClient.open("GET", "listeners_serv.php", true);
  listenerClient.send(null);
}
function listenerHandler() {
 if(listenerClient.readyState == 4 && listenerClient.status == 200) {
  if(listenerClient.responseText != null) {
   updateListenerDiv(listenerClient.responseText);
   } else {
    return 0;
   }
 } else {
  return 0;
 }
}
function updateListenerDiv(data) {
  var divListener=document.getElementById("listeners");
  divListener.innerHTML=data;
  if (window.XMLHttpRequest) { // Mozilla, Safari, ...
      listenerClient = new XMLHttpRequest();
  } else if (window.ActiveXObject) { // IE
      listenerClient = new ActiveXObject("Microsoft.XMLHTTP");
  }
  listenerClient.onreadystatechange = listenerHandler;
  setTimeout("startListenerUpdate()",30000);
}