code: function checkState() {
                  try {
                      var state = getDoc(io).readyState;
                      log('state = ' + state);
                      if (state && state.toLowerCase() == 'uninitialized')
                          setTimeout(checkState,50);
                  }
                  catch(e) {
                      log('Server abort: ' , e, ' (', e.name, ')');
                      cb(SERVER_ABORT);
                      if (timeoutHandle)
                          clearTimeout(timeoutHandle);
                      timeoutHandle = undefined;
                  }
              }
docs: look for server aborts