I'm conflicted - the spec uses web IDL, which is incessantly over-prescriptive - I think in the context of a JS implementation, since there's no way to *not* set the key as the string form, it's not necessary - in addition, this is just the string form of the `i` var, which is always an integer - so while it can't hurt, it might make things slightly less performant while not actually providing any benefit.

Either way, it's minor.