function createRequestObject() {

   var req;

   if(window.XMLHttpRequest){
      // Firefox, Safari, Opera...
      req = new XMLHttpRequest();
   } else if(window.ActiveXObject) {
      // Internet Explorer 5+
      req = new ActiveXObject("Microsoft.XMLHTTP");
   } else {

      alert('Problem creating the XMLHttpRequest object');
   }

   return req;

}

var http = createRequestObject();