On Sep 11, 2013, at 6:07 PM, Boris Zbarsky <[email protected]> wrote: > 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]] > athttp://dev.w3.org/2006/webapi/WebIDL/#named-properties-object and > http://dev.w3.org/2006/webapi/WebIDL/#interface-prototype-object (item 1 at > the latter).
Ah, got it, thanks. I’d only spotted the partial description in http://dev.w3.org/2006/webapi/WebIDL/#Global > 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 Window.prototype! > >> 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. Got it. >> (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. Hmmm, interesting. I was thinking that in the case that a shadowing property was put to the named property object itself, then deleted, this needed further description (as the old property reappears) – but I guess that it just covered by the current spec [[GetOwnProperty]] implementation. Many thanks, Gavin
