Allen Wirfs-Brock wrote:
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.
This isn't what we seemed to agree on at past TC39 meetings.
It's also not what the engines trying to converge on ES6 semantics have
implemented.
/be
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
<http://wiki.ecmascript.org/lib/exe/fetch.php?id=meetings:meeting_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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