I presume that we can having null prototype means being on top of the inheritance chain, hence the correct answer for that case would be 0, same as for plain {}.

Added an example test case for showing that.

Thanks, updated random test.

Thank you for your note.

Added a clarification for that issue:

So, every prototype actually inherits Object through inheritance chain (except for Object prototype itself, which has null prototype, and prototypes created with Object.create(null)).

Added random tests, please check.

Thank you dolamroth, very cool