My takeaway from this thread is that there is support for the proposed
__proto__ semantics on the wiki [1], with a few modifications/additions. Are
the following a correct summary of the deltas?
*** Accessor vs. Data property
Although there does not appear to be a direct security implication of exposing
Object.prototype.__proto__ as a true accessor property, there is a desire to be
conservative about exposing new __proto__ capabilities beyond what is actually
defacto available on browsers today. As a result, the initial value of
__proto__ should appear as a data property to developers, but remain internally
an accessor property.
*** Object literals
The wiki does not currently discuss the semantics of __proto__ in object
literals. Given the desire to allow __proto__ to be removed, it seems more
details are needed to nail down what this does:
delete Object.prototype.__proto__
{ __proto__: {x: 1} }
I believe there are two options:
(1) __proto__ in object literals always sets the [[Prototype]], irrespective
of the value of Object.prototype.__proto__ or
(2) __proto__ is treated as a [[Put]] instead of a [[DefineProperty]] in the
Object Intialiser rules
The second option appears more inline with the goals of the wiki proposal.
When there are multiple __proto__ in an object literal, I believe it has been
suggested that this produce a SyntaxError.
*** JSON
I believe there is a requirement that JSON.parse('{"__proto__": {}}') return
an object with an own data property named __proto__ whose value is {}.
Browsers currently disagree on this though.
Thanks,
Luke
[1] http://wiki.ecmascript.org/doku.php?id=strawman:magic_proto_property
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