On Tue, Jan 27, 2015 at 7:22 PM, Brendan Eich <bren...@mozilla.org> wrote:
> Mark S. Miller wrote: > >> The reason why the intent is unwarranted is that the descriptor omits >> "configurable:" rather than explicitly saying "configurable: true". If the >> owner object already has a configurable own property of the same name, then >> a defineProperty where the "configurable:" is omitted defines an own >> property preserving the configurability of the original own property. >> > > Wild, and genius. (blush) > How many more narrow escapes can we make and keep both web compat and > integrity? :-P > How many will we need? ;) > > Is there any downside? What is the bad case that observably changes > behavior, if any (not involving proxies)? You get the following non-intuitive but allowed behavior. if (!hasOwnProperty(W, P)) { defineProperty(W, P, { value: V }) console.log(getOwnPropertyDescriptor(W, P).configurable); // true } However, you could also get this behavior if W is a proxy, so it doesn't introduce any new cases beyond what's already possible. It is only surprising. That's not much of a downside, and I can't think of any other downside. I'm too tired to search the state space right now, throwing this out as a > challenge. -- Cheers, --MarkM
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