New ES6 draft now available

Tom Van Cutsem at
Mon Nov 26 09:44:02 PST 2012

2012/11/25 Allen Wirfs-Brock <allen at>

> On Nov 25, 2012, at 12:41 PM, Tom Van Cutsem wrote:
> However, with [[HasProperty]] removed, I assume the "in"-operator no
> longer triggers the "has" trap when it encounters a proxy, instead doing
> the proto-chain-walk itself and calling "hasOwn" on each level. This is OK,
> although it introduces an inconsistency with the other proto-chain-walking
> algorithms, which stop when encountering a proxy, letting the proxy take
> over from that point (this is the case for the "get", "set" and "enumerate"
> traps).
> [[HasProperty]] is replaced with a HasProperty abstract operation (9.3.6)
> that indeed makes generic calls to [[HasOwnProperty]] and
> [[GetInheritance]]  in a loop.  This also slightly bothers me. I guess I
> convinced my self that an object that wanted to use a non-standard
> inheritance path could hide that by reporting its inherited properties to
> be own properties.
> I also occasionally find it troubling  inheritance semantics are
> replicated in three different places [[GetP]], [[SetP]], and HasProperty
> and that it is quite possible to get them out of sync.   I've come to
> accept the replication/possible inconsistency but maybe we really do need
> to bring back [[HasProperty]] so that it is possible to consistently
> over-ride all three.  I'd might be happy to swap
> [[Feeze]]/[[Seal]]/i[[sFrozen]]/[[isSealed]] for [[HasProperty]]  :-)

Yes, this is a good point: one must be able to consistently override all
inheritance-related operations. Requiring an object with multiple
prototypes to report all inherited properties as "own" feels broken.

W.r.t. freeze and friends, I thought you were considering a more generic
[[GetIntegrity]]/[[SetIntegrity]] operation.

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