var ajaxreq=false, ajaxCallback;
function ajaxRequest(filename,mode) {
  try {
    ajaxreq=new XMLHttpRequest();
  } catch (error) {
    try {
      ajaxreq=new ActiveXObject("Microsoft.XMLHTTP");
    } catch (error) {
      return false;
    }
  }
  ajaxreq.open("GET", filename,mode);
  ajaxreq.onreadystatechange=ajaxResponse;
  ajaxreq.send(null);
}

function ajaxResponse() {
  if(ajaxreq.readyState!=4) return;
  if(ajaxreq.status==200) {
    if(ajaxCallback) ajaxCallback();
  } else alert("Request failed: "+ajaxreq.statusText);
  return true;
  }