Fx4 (SpiderMonkey)'s behaviour is valid in ES5 spec.
Assignment to Object Property Reference (obj.prop = "own") call
[[Put]] internal method.
[[Put]] checks "this value can be put" by calling [[CanPut]].
[[CanPut]] checks inherited PropertyDescriptor in 8.12.4-5, and in
this case, variable "inhrerited" is PropertyDescriptor of
Ctor.prototype.prop. Because inherited.[[Writable]] is false,
[[CanPut]] returns false (8.12.4-8-b) and [[Put]] rejects this
assignment.
thanks.
On Sat, Mar 12, 2011 at 11:19 PM, michalr <michal.raczkow...@gmail.com> wrote:
> Hello,
> I discovered that the following ES5 code evaluates differently in FF4
> than Chrome and Safari.
>
>
> function Ctor() {};
> Object.defineProperty(Ctor.prototype, "prop", {
> value: "prototype",
> writable: false
> });
>
> var obj = new Ctor();
> obj.prop = "own";
> alert(obj.prop + ", " + obj.hasOwnProperty("prop"));
>
>
> Chrome and Safari gives: "own, true".
> FF4 gives: "prototype, false".
>
> Could anybody explain why?
>
> greetings
> Michal
>
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