code: function _cb(err, result) {
      if (result && result._class === 'hudson.model.Queue$LeftItem') {
        cb(true);
      } else {
        cb(false);
      }
    }
docs: hudson.model.Queue$WaitingItem indicates that the item is still waiting in the queue hudson.model.Queue$LeftItem indicates that the item left the queue and the build has started