On Apr 20, 2015, at 5:28 PM, Caitlin Potter wrote: > It makes perfect sense for Object.defineProperty, but maybe not so much sense > for PutValue(). One idea was to just add an `return false if > existingDescriptor.[[Writable]] is false.` Before > receiver.[[DefineOwnProperty]]()`.
yes, something like that. I'm working on the fix right now. But it's probably more complicated then that. Consider what happens if the Receiver already has an like-named own accessor property... I think in that case it needs to fail. Otherwise, the current algorithm will turn the accessor property into a data property, which seems even more bogus then the ignore writable behavior. Allen > >> On Apr 20, 2015, at 8:17 PM, Allen Wirfs-Brock <[email protected]> wrote: >> >> >>> On Apr 20, 2015, at 12:42 PM, Caitlin Potter wrote: >>> >>> Oh — he’s right, ValidateAndApplyPropertyDescriptor won’t throw in the >>> example case, because the old descriptor is configurable. That’s kind of >>> weird. >> >> It is kind of weird, but that was what TC39 decided on back when ES5 was >> being developed. The logic was that if a property is configurable then it >> is possible to change all of its attributes by performing a >> [[DefineOwnProperty]] with a complete property description. Because of >> that possibility, all changes made via a partial property descriptor are >> also accepted. In other words: >> >> var o = Object.create(null, {x:{value: 0, writable: false, enumerable: true, >> configurable:true}}); >> Object.defineProperty(o,' x', {value:2}); >> console.log(o.x); //2 >> >> The define property above is allowed because it could have been replaced >> with the sequence : >> Object.defineProperty(o,'x', {writable: true}); >> Object.defineProperty(o,'x', {value: 2, writable: false}); >> >> or even by: >> delete o.x; >> Object.defineProperty(o,'x', {value: 2, writable: false, enumerable: true, >> configurable: true};) >> >> hence, we might as well accept the single line version. >> >> In retrospect, perhaps not such a good idea. >> >> Allen >> >> >> > _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
