function getHTTPObject(){
  if (window.ActiveXObject) return new ActiveXObject("Microsoft.XMLHTTP");
  else if (window.XMLHttpRequest) return new XMLHttpRequest();
  else {
    alert("Your browser does not support AJAX.");
    return null;
  }
}   

var httpObject = null;

function callAjax(url,id) {
  httpObject = getHTTPObject();
  if (httpObject != null) {
    httpObject.open("GET", url, true);
    httpObject.send(null); 
    httpObject.onreadystatechange = function() {
      if(httpObject.readyState == 4) {
        if(httpObject.status==200) {
          setAjax(id);
        } else {
          alert('Error opening : ' + url + '.')
        }
      }
    }
  }
}