Le 02/11/2012 16:39, Allen Wirfs-Brock a écrit : > So, yes, in that case Object.getOwnPropertyDescriptor and > Object.defineProperty need to pass through object level descriptors > from/to the corresponding proxy traps which means they can't normalize > via a property descriptor record. So, it is perfectly appropriate for > them to explicitly test if O is a proxy and act accordingly. I > think, this should be the only place where an explicit Proxy test is > required outside of the actual proxy object specification algorithms. For some time after this sentence I wondered what justified Object.getOwnPropertyDescriptor and Object.defineProperty to have special-casing for proxies. The reason is that proxies have an additional ability that regular objects don't: accepting custom attributes. More specifically, proxies are expected to be able to regurgitate custom attributes on Object.getOwnPropertyDescriptor after they've been set with Object.defineProperty.
Then, I wondered why it matters that only proxies can do it. The reason is future-proofing. If a property descriptor record accepts any key and value besides the standards ones, then it may become impossible to extend property descriptor records in the future by assigning semantics to currently-unused field names. Keeping property descriptor records as tightly defined is for the best for the future. David _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
