//----------------------------------------------------------------
//--- AJAX helper library
//----------------------------------------------------------------
//
// Define a list of Microsoft XML HTTP ProgIDs.
//
var XMLHTTPREQUEST_MS_PROGIDS = new Array(
  "Msxml2.XMLHTTP.7.0",
  "Msxml2.XMLHTTP.6.0",
  "Msxml2.XMLHTTP.5.0",
  "Msxml2.XMLHTTP.4.0",
  "MSXML2.XMLHTTP.3.0",
  "MSXML2.XMLHTTP",
  "Microsoft.XMLHTTP"
);

//
// Define ready state constants.
//
var XMLHTTPREQUEST_READY_STATE_UNINITIALIZED = 0; // open() has not been called
var XMLHTTPREQUEST_READY_STATE_LOADING       = 1; // open() has been called but send() has not been called
var XMLHTTPREQUEST_READY_STATE_LOADED        = 2; // send() has been called and the response status and headers have been received
var XMLHTTPREQUEST_READY_STATE_INTERACTIVE   = 3; // the response data is being downloaded
var XMLHTTPREQUEST_READY_STATE_COMPLETED     = 4; // the request has completed and all response data has been downloaded

//
// Returns XMLHttpRequest object.
//
function getXMLHttpRequest() {
  var httpRequest = null;

  // Create the appropriate HttpRequest object for the browser.
  if (window.XMLHttpRequest != null)
    httpRequest = new window.XMLHttpRequest();
  else if (window.ActiveXObject != null) {
    // Must be IE, find the right ActiveXObject.
    var success = false;
    for (var i = 0; i < XMLHTTPREQUEST_MS_PROGIDS.length && !success; i++) {
      try {
        httpRequest = new ActiveXObject(XMLHTTPREQUEST_MS_PROGIDS[i]);
        success = true;
      } catch (ex) {
	  }
    }
  }

  // Display an error if we couldn't create one.
  if (httpRequest == null)
    alert("Error in HttpRequest():\n\nCannot create an XMLHttpRequest object.");

  // Return it.
  return httpRequest;
}