var xmlrequest;
function newXMLHttpRequest() {
  var xmlreq = false;  
  if (window.XMLHttpRequest) {
  
    xmlreq = new XMLHttpRequest();
  } else if (window.ActiveXObject) {
  
    try {    
      xmlreq = new ActiveXObject("Msxml2.XMLHTTP");      
    } catch (e1) {
    
      try {
        xmlreq = new ActiveXObject("Microsoft.XMLHTTP");
      } catch (e2) {
      }
    }
  }
  return xmlreq;
}
//send a request to server with url
function sendRequestToSetSession(url)
{	
	xmlrequest=newXMLHttpRequest();
	xmlrequest.onreadystatechange=callback;
	xmlrequest.open("get",url,true);
	xmlrequest.send(null);
}
//if username is validate then return YES
// if not validate then return NO
function callback(){
	if(xmlrequest.readyState==4){
		if(xmlrequest.status==200){

		}
	}
}