On Nov 29, 2014, at 3:38 PM, Nicholas C. Zakas wrote:
> In Rev 28, B.3.1 it states:
> It is a Syntax Error if PropertyNameList of PropertyDefinitionList contains
> any duplicate entries for"__proto__" and at least two of those entries were
> obtained from productions of the formPropertyDefinition : PropertyName :
> AssignmentExpression .
> I noted that the duplicate name restriction was eliminated back in July[1]
> and was just wondering if __proto__ is indeed a special case?
>
> Thanks.
>
> [1]
> https://github.com/rwaldron/tc39-notes/blob/46d2396e02fd73121b5985d5a0fafbcdbf9c9072/es6/2014-07/jul-29.md#41-review-latest-draft
Yes, `__proto__ : <expr>` in an object literal is a special form with
different semantics than the other PropertyDefinition forms. The relaxation of
the duplicate entry was explicitly not applied to it.
It's worth noting that:
__proto__: <expr>
and
["__proto__"] : <expr>
do not mean the same thing.
The first form does a [[SetPrototypeOf]] and is the form that the above early
error applies to.
The second form does a [[DefineProperty]] and does not place any restrictions
of duplicates.
Allen
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