var request = false;
   try {
     request = new XMLHttpRequest();
   } catch (trymicrosoft) {
     try {
       request = new ActiveXObject("Msxml2.XMLHTTP");
     } catch (othermicrosoft) {
       try {
         request = new ActiveXObject("Microsoft.XMLHTTP");
       } catch (failed) {
         request = false;
       }  
     }
   }
 if (!request)
     alert("Error initializing XMLHttpRequest!");
   var url = "viewer.aspx";
   request.open("GET", url, true);
   request.onreadystatechange = viewer;
   request.send(null);	
 function viewer(){
  if (request.readyState == 4)
  {
       if (request.status == 200)
       {
       var response = request.responseText;
        }
      else if (request.status == 404)
         alert("Request URL does not exist");
       else
         alert("Error: status code is " + request.status);	
	}else{
	
	}
	
}