Perhaps @@unscopable shouldn't be a Set...

Brendan Eich brendan at
Wed Apr 30 11:36:50 PDT 2014

Including Tom because proxies and MOP.


Erik Arvidsson wrote:
> This was never resolved and the spec is incomplete here
> On Wed Sep 25 2013 at 6:17:32 PM, Allen Wirfs-Brock 
> <allen at <mailto:allen at>> wrote:
>     So here is another concern, about the scheme we agreed to last week.
>     It needs to match a found own property against the possibility of
>     an own @@unscopable property on the same object and that  object
>     may be somewhere up the inheritance chain of the actual with
>     object.  The means that [[HasProperty]]/[[Get]]/[[Set]] can not be
>     used to do those resolve binding in an ObjectEnvironmentRecord
>     because they don't tell us where the property was found.  Instead,
>     ObjectEnvironmentRecord needs to reimplement its own property
>     lookup using [[GetOwnProperty]] and [[GetInheritanceOf]].
>      However, if the with object is a proxy that means we may be
>     bypassing the actual inheritance mechanism implemented by the
>     Proxy's 'has'/'get'/'set' traps and that could introduce
>     observable semantics irregularities.
>     Specifying the duplicated lookup is doable but a pain.  That and
>     the semantic issues WRT proxies makes me a lot less comfortable
>     with the added complexity of supporting @@unscopable.
>     Allen 

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