[whatwg] [[GetOwnProperty]] for named properties of the Window object
bzbarsky at MIT.EDU
Wed Sep 11 18:07:54 PDT 2013
On 9/11/13 6:05 PM, Gavin Barraclough wrote:
> Interesting, I had just assumed this was okay – is it not spec-compliant for Window.prototype to be a named properties object?
No, it's not. The spec defines exactly what the prototype chain looks
like here. See the definitions of [[Prototype]] at
http://dev.w3.org/2006/webapi/WebIDL/#interface-prototype-object (item 1
at the latter).
So the chain by default is window -> Window.prototype -> named
properties object -> EventTarget.prototype -> Object.prototype.
This allows specification of the named properties object without having
to worry about weird interactions with name collisions on
Window.prototype, whether with properties it has by default or
properties someone wants to add to it. Note that the named properties
object does not allow [[DefineOwnProperty]], so if it were
Window.prototype then you wouldn't be able to add any properties to
> I believe these properties are implemented as shadowable in the same way as [Replaceable] properties
[Replaceable] properties need the magic they have because they're
accessor properties, which normally can't be shadowed via assignment.
But named properties on the named properties object are value
properties, so simply making them writable allows them to be shadowed.
In fact, that's the only way to make them shadowable.
> (and then assume a modified behaviour of ES [Put] for properties with this attribute, to permit overwrite even if readonly).
I don't think a special [Put] is needed if the properties aren't readonly.
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