var request = null;
function createRequest() {

try {
  request = new XMLHttpRequest();
} catch (trymicrosoft) {
  try {
    request = new ActiveXObject("Msxml2.XMLHTTP");
  } catch (othermicrosoft) {
    try {
      request = new ActiveXObject("Microsoft.XMLHTTP");
    } catch (failed) {
      request = null;
    }
  }

}

if (request == null)
  alert("Error creating request object!");

 }

var class_id="";

var subject_id="";


function getTopics()
 {
  createRequest();   
  class_id=document.getElementById('select_class').value;
  subject_id=document.getElementById('select_subject').value;
  var url = "audio_ajax_user.php?oper=getTopics&class_id="+class_id+"&subject_id="+subject_id ;
  request.open("GET", url, true);
  request.onreadystatechange = showClassRecords;
  request.send(null);

}


function showClassRecords()
{
if (request.readyState == 4) {
    if (request.status == 200) {
    document.getElementById("topic").innerHTML =request.responseText;
	}
  }
}