B.3.1 The __proto__ pseudo property

Brendan Eich brendan at mozilla.com
Tue Apr 23 06:37:23 PDT 2013

Andreas Rossberg wrote:
> On 22 April 2013 22:15, Allen Wirfs-Brock<allen at wirfs-brock.com>  wrote:
>> We don't currently have the concept of an object "belonging" to a realm.  Functions have a realm association, but not non-function object.
> I thought the current plan of record is to require this check for
> reflected uses of protosetter.call? So I don't see how we can avoid
> introducing that concept (and to answer Mark's question re
> implementation: in V8 at least it has always been available -- it may
> be that the DOM already requires it, but I'm not sure).

In practice, all engines must classify objects by realm, somehow. 
Usually by GC-page-cluster or "compartment".

> My only new(?) observation was that we already need that check for
> unreflected uses if we are serious about maintaining the invariant
> that I thought we intended to maintain. And as a consequence, we don't
> actually need any magic for __proto__. You should like that. :)

Yes! The magic goes away (except that ({__proto__: ...}) is still a 
special form).


More information about the es-discuss mailing list