Rw-asking: a weaklist that doesn't work and an object with elements that can't be copied or queried

Hello all,

Over two weeks ago I posted a question with the subject "JS log-dumping an 
object and circular references problem".   Although I've been able to create 
something that seems to work, two questions remain :

A "weaklist" that could solve the "circular references" problem does not 
want to have objects added to it.
Reference : seen.add(value))

Trying to copy one of the objects elements into a variable fails.  Directly 
trying to inspect the element fails to
Reference : var value = arr[item]
Also : typeof(arr[item])

I would appriciate it if someone could explain the failure of either of the 
above to me.

Regards,
Rudy Wieser