code: function _cleanObserver(observer) {
          if (!attachedNotifierCountMap.get(observer) && !pendingChangesMap.has(observer)) {
              attachedNotifierCountMap.delete(observer);
              var index = observerCallbacks.indexOf(observer);
              if (index !== -1) {
                  observerCallbacks.splice(index, 1);
              }
          }
      }
docs: Remove reference all reference to an observer callback, if this one is not used anymore. In the proposal the ObserverCallBack has a weak reference over observers, Without this possibility we need to clean this list to avoid memory leak