Allen Wirfs-Brock wrote:
On Apr 21, 2013, at 10:03 AM, Brendan Eich wrote:
Allen Wirfs-Brock wrote:
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.
It's not clear to me, yet what convergence we actually have.
Read the meeting notes to remind yourself:
https://mail.mozilla.org/pipermail/es-discuss/2013-February/028631.html
Look for
BE: (Review of latest changes to __proto__ in Firefox)
and read on.
Regardless, it's only observable via Object.getOwnPropertyDescriptor(Object.prototype,
"__proto__") which in my proposal returns undefined when Dunder proto is active
and in other proposals returns a function that when evaluated throws something.
No. From those notes:
EA: Throws if called with object and setter coming from different realms
The semantics of Dunder proto that have been discussed isn't just that of
an accessor property and can't be purely implemented as such so I no value in
trying to masquerade it as an accessor for getOwnPropertyDescriptor. Returning
get/set functions that always throws is just adding complexity that delivers no
value.
The proposal we've discussed does no such thing. What's implemented in
JSC, SpiderMonkey, V8 does no such thing.
js> var d = Object.getOwnPropertyDescriptor(Object.prototype, '__proto__')
js> d
({configurable:true, enumerable:false, get:function () {
[native code]
}, set:function () {
[native code]
}})
js> var o = {}
js> d.get.call(o)
({})
js> d.get.call(o) === Object.prototype
true
js> d.set.call(o, null)
js> d.get.call(o)
null
The censorship requires a realm-check. That seems (and seemed, to TC39
in January) better than a wart in Object.getOwnPropertyDescriptor that
turns a blind eye to the existence of '__proto__' in Object.prototype in
contradiction to plainly observable facts!
/be
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