code: function _xdr(url) {
          return new Promise(function(resolve, reject) {
              var req = new XMLHttpRequest();
              req.open('get', url);
              req.onerror = reject;
              req.onreadystatechange = function onreadystatechange() {
                  if (req.readyState === 4) {
                      if ((req.status >= 200 && req.status < 300) ||
                          (url.substr(0, 7) === 'file://' && req.responseText)) {
                          resolve(req.responseText);
                      } else {
                          reject(new Error('HTTP status: ' + req.status + ' retrieving ' + url));
                      }
                  }
              };
              req.send();
          });
  
      }
docs: Make a X-Domain request to url and callback.
  
  @param {String} url
  @returns {Promise} with response text if fulfilled