XHR and fallback

XHR.js

// simple request with a fallback

function getXHR() { 
  if (window.XMLHttpRequest) {
    return new XMLHttpRequest(); 
  } 
  try { 
    return new ActiveXObject('MSXML2.XMLHTTP.6.0');
  }
  catch (err) { 
    try { 
      // fallback.
      return new ActiveXObject('MSXML2.XMLHTTP.3.0');
    }
    catch (err) { 
      alert('AJAX is not enabled.'); 
      return null;
    } 
  } 
}