var http_request = false;

function makeRequest(url) {

   if (window.XMLHttpRequest) { // Mozilla, Safari,...
       http_request = new XMLHttpRequest();
   } else if (window.ActiveXObject) { // IE
       http_request = new ActiveXObject("Microsoft.XMLHTTP");
   }
   http_request.onreadystatechange = alertContents;
   http_request.open('GET', url, true);
   http_request.send(null);

}

function alertContents() {

   if (http_request.readyState == 4) {
       if (http_request.status == 200) {
           //alert(http_request.responseText);
       } else {
           alert('There was a problem with the request.');
       }
   }

}