On Wed, Jan 28, 2015 at 8:51 AM, Domenic Denicola <d...@domenic.me> wrote:
> From: Mark S. Miller [mailto:erig...@google.com] > > > On Tue, Jan 27, 2015 at 5:53 PM, Boris Zbarsky <bzbar...@mit.edu> wrote: > >> I'd like to understand better the suggestion here, because I'm not sure > I'm entirely following it. Specifically, I'd like to understand it in > terms of the internal methods defined by < > https://github.com/domenic/window-proxy-spec>. > >> > >> Presumably you're proposing that we keep all of that as-is except for > [[DefineOwnProperty]], right? > >> > >> For [[DefineOwnProperty]], are we basically talking about changing step > 1 to: > >> > >> 1) If the [[Configurable]] field of Desc is present and > Desc.[[Configurable]] is false, then throw a TypeError exception. > >> > >> while keeping everything else as-is, > > > > Exactly correct. I didn't realize until reading your reply is that this > is all that's necessary -- that it successfully covers all the cases I was > thinking about without any further case division. > > I'm having a bit of trouble understanding how this maps to the solution > described in your previous message, Mark. Your "I didn't realize until > reading your reply is that this is all that's necessary" indicates I'm > probably just missing something, so help appreciated. > > My question is, what happens if Desc.[[Configurable]] is not present, and > P does not already exist on W? By my reading, we then fall through to > calling the [[DefineOwnProperty]] internal method of W with arguments P and > Desc. > > Assuming W's [[DefineOwnProperty]] is that of an ordinary object, I > believe that takes us through OrdinaryDefineOwnProperty(W, P, Desc). Since > P does not exist on W, and W is extensible, that takes us to > ValidateAndApplyPropertyDescriptor(O, P, true, Desc, undefined). Then > according to step 2.c, " If the value of an attribute field of Desc is > absent, the attribute of the newly created property is set to its default > value." The default value is false, right? So won't this try to define a > non-configurable property on W? > In this situation, it will try and succeed. This more closely obeys the intent in the original code (e.g., the comment in the jQuery code), since it creates a non-configurable property on the *Window* W. It does not violate any invariant, since all that's observable on the *WindowProxy* (given the rest of your draft spec, which remain unchanged) is a configurable property of the same name. > > I would have thought the modification needed to be more like: > > [[DefineOwnProperty]] (P, Desc) > > 1. If desc.[[Configurable]] is not present, set desc.[[Configurable]] to > true. > 2. If desc.[[Configurable]] is false, then throw a TypeError exception. > 3. Return the result of calling the [[DefineOwnProperty]] internal method > of W with arguments P and Desc. > > (here I have inserted step 1, but step 2 and 3 are unchanged from the > previous incarnation). > -- Cheers, --MarkM
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