Le 02/11/2012 12:20, Tom Van Cutsem a écrit : > Hi Allen, > > 2012/11/1 Allen Wirfs-Brock <al...@wirfs-brock.com > <mailto:al...@wirfs-brock.com>> > > The above isn't how this will be expressed in the final spec. > Instead we will have > > 3) Let desc be the result of calling the [[GetOwnProperty]] internal > method of O with argument name. > 4) Return the result of calling FromPropertyDescriptor(desc) (8.10.4). > > And all Proxy objects will have a [[GetOwnProperty]] internal > methods that looks something like: > > 1) Let O be the object upon which this internal method was invoked. > 2) Let desc be the result of calling TrapGetOwnProperty(O,name) > 3) Return ToPropertyDescriptor(desc) > > (I left out details of exception handling) > > > Actually, while reviewing the spec, I realized that there is a good > reason why the spec isn't currently specified this way (i.e. why > the Proxy spec redefines Object.defineProperty and > Object.getOwnPropertyDescriptor and does not just override > [[DefineOwnProperty]] and [[GetOwnProperty]]) > > It is to avoid the lossy conversion that otherwise occurs between the > return value of [[GetOwnProperty]] and Object.getOwnPropertyDescriptor. Just to be sure I fully understand: what is the loss exactly? I see that custom property descriptor attributes would be stripped out (because FromPropertyDescriptor outputs an object with 4 props mapping 1-to-1 to an accessor or data property descriptor). Is there another loss?
If that's the only thing, redefining the property descriptor type to accept any field would prevent that loss. Such a change would be more aligned with the intention in the proxy spec of letting internal operations manipulate custom attributes passed to Object.defineProperty. I'm arguing in favor of switching to a script-usable type, but the change I mention can occur in the spec-only type. David
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