jdarling/Object.observe — pull request #6 by moshemal (2013-12-31 16:01:59+00:00)
Title: Memory leak issue. Delete a notifier with no callbacks. This is done in Object.unobserve

Without the proposed modification, after calling:
Object.observe(someObject, someCallback);
Object.unobserve(someObject, someCallback);
A notifier for someObject and a reference to someObject will exist even if someObject is not used anymore.
This can cause a memory leak