Unscopeable

Erik Arvidsson erik.arvidsson at gmail.com
Wed Aug 21 07:46:55 PDT 2013


On Wed, Aug 21, 2013 at 10:07 AM, Andreas Rossberg <rossberg at google.com> wrote:
> On 21 August 2013 15:41, Erik Arvidsson <erik.arvidsson at gmail.com> wrote:
>> One way to think of it is that the with is acting on a view of the
>> object that does not have the blacklisted properties. This can be
>> implemented using proxies. I'll leave that as an exercise.
>
> I see.
>
>>> * How would it interact with mutation?
>>
>> Another hole we didn't cover. Here is my proposal:
>>
>> The @@unscopable is only accessed once, when the object environment
>> record is created.
>
> Hm, that would seem rather inconsistent with the way adding/removing
> properties can dynamically change the domain of a 'with'. Consider:
>
>   function safeenrich(o) {
>     o.a = 1
>     o[@@unscopable] = o[@@unscopable] || []
>     o[@@unscopable].push('a')
>   }
>
>   let o = {}
>   let a = 0
>   with (o) {
>     a  // 0
>     safeenrich(o)
>     a  // 1
>   }

I don't think it is worth covering these kind of new scenarios. We are
patching a broken feature here.

Still, it is easy to allow that if we really wanted to. We can make
ObjectEnvironment [[HasBinding]] do object.[[Get]](@@unscopeable)
every time then.

-- 
erik


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