Hi,
ES5 invariants are silent when it comes to function identity of
non-configurable accessors. That is, for a given object o,
Object.getOwnPropertyDescriptor(o, 'a').get ===
Object.getOwnPropertyDescriptor(o, 'a').get
(two seperate calls) is not guaranteed.
The built-in [[DefineOwnProperty]] (ES5.1 - 8.12.9) prevents from
changing of getter and setter functions when the property is not
configurable (step 11), but that's not an expected invariant for
self-hosted objects.
I think that the current definition of non-compatible descriptors (based
on Object.getOwnPropertyDescriptor and Object.defineProperty) used in
invariant checks makes impossible to use different functions and that
may be a problem.
The way things are going, WindowProxy [Unforgeable] properties will be
non-configurable getters. If, upon underlying window change, the
WindowProxy is expected to keep the exact same getter function, then, it
may result in capability leaks (attach something in a getter in one
iframe and get it back when the iframe@src has changed). One solution
could be to make these getters frozen; a better solution would be to not
"same getter identity" as an invariant for proxies reflecting
non-configurable accessors.
David
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