code: function getXhrOrXdr(id, suppliedXhr) {
          var xhrOrXdr = requestData[id] && requestData[id].xhr;
  
          if (!xhrOrXdr) {
              if (suppliedXhr) {
                  xhrOrXdr = suppliedXhr;
              }
              else {
                  if (options.cors.expected) {
                      xhrOrXdr = getCorsAjaxTransport();
                  }
                  else {
                      xhrOrXdr = qq.createXhrInstance();
                  }
              }
  
              requestData[id].xhr = xhrOrXdr;
          }
  
          return xhrOrXdr;
      }
docs: Returns either a new XHR/XDR instance, or an existing one for the associated `File` or `Blob`.