code: function _getNotifier(target) {
          if (!notifierMap.has(target)) {
              var notifier = Object.create(NotifierPrototype);
              // we does not really need to hide this, since anyway the host object is accessible from outside of the
              // implementation. we just make it unwritable
              Object.defineProperty(notifier, '__target', { value : target });
              changeObserversMap.set(notifier, []);
              activeChangesMap.set(notifier, {});
              notifierMap.set(target, notifier);
          }
          return notifierMap.get(target);
      }
docs: Implementation of the internal algorithm 'GetNotifier' described in the proposal. [Corresponding Section in ECMAScript wiki](http://wiki.ecmascript.org/doku.php?id=harmony:observe_internals#getnotifier)