On Apr 21, 2013, at 5:22 AM, David Bruant wrote:
> Hi Axel,
>
> Le 21/04/2013 01:37, Axel Rauschmayer a écrit :
>> __proto__ can be globally switched off by deleting
>> Object.prototype.__proto__. I’m assuming that that is useful for
>> security-related applications (Caja et al.). But I’m wondering: doesn’t that
>> go too far? I’m seeing three ways of using __proto__:
>>
>> 1. Read the [[Prototype]] of an object. Already possible via
>> Object.getPrototypeOf().
>> 2. Set the [[Prototype]] of a fresh object created via an object literal
>> (i.e., an alternative to the rejected <| operator). Already (kind of)
>> possible via Object.create().
> Also possible with class syntax and the "extends" keyword (with all the
> @@create internal semantics).
>
>> 3. Mutate the [[Prototype]] of an existing object.
>>
>> Globally, I would only want to switch off #3.
> You can re-enable #1 by re-adding Object.prototype.__proto__ as your own
> getter wrapping Object.getPrototypeOf. Or maybe instead of "delete
> Object.prototype.__proto__", just do:
> Object.defineProperty(Object.prototype, "__proto__", {set: undefined});
I still think that Dunder proto should not be exposed at all by
Object.getOwnPropertyDescriptor (or any other reflection) and that there is no
need to leak either a working or always throwing __proto__ setter function into
the hands of a ES programmer.
My preferred spec for it is at
http://wiki.ecmascript.org/lib/exe/fetch.php?id=meetings%3Ameeting_may_21_2013&cache=cache&media=meetings:rev_15_proto_.pdf
Note that the behavior that some people have expressed a preference for (Dunder
proto is observably an accessor property but its set function when retrieved
always throws) will also require an exotic Object prototype object to specify
so my proposal is not adding any spec. complexity.
As an exercise to the reader, it isn't hard to demonstrate that specified
approach could be expressed by using a Proxy to defined Object.prototype (if
the proxy handler had access to [[SetInheritance]]). Since proxy objects are
allowed to occur on the [[Prototype]] chain, if an implementation has the
mechanism to implement Proxy it will also have the mechanism necessary to
implement this definition of Dunder proto.
Allen
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