I wonder if v8 can optimise that if the object is constructed such that it can infer a 'type' for it (IIRC if v8 can see the list of keys at object construction

I wonder if v8 can optimise that if the object is constructed such that it can infer a 'type' for it (IIRC if v8 can see the list of keys at object construction time it remembers what they are for a bunch of things, no idea if this is one of them.)