[webkit-dev] Question about Constructors in WebKit JS Bindings

[Adam Barth]

On Tue, Jul 7, 2009 at 6:29 PM, Drew Wilson<atwilson at google.com> wrote:
> Interesting - I ran some tests on both current WebKit and Firefox.
> Firefox has a couple of interesting properties. For example this code:
> Worker.prototype.foo = 3;
> log("Worker.prototype.foo = " + Worker.prototype.foo);
> var worker = new Worker("foobar.js");
> log("worker.foo = " + worker.foo);
> yields:
> Worker.prototype.foo = 3
> worker.foo = undefined
> in Firefox, while in Safari it yields worker.foo = 3 as expected.

This is a good test, but I would test something older than the Worker
constructor.  For example, the Image constructor might be a good
choice.

> Along those same lines:
> new Worker().__proto__ == Worker.prototype
> yields true on Safari, but false on Firefox, which seems broken to me.

In this kind of test, you want to use === to avoid being tricked by valueOf.

> This is all within the same page (no frames). I've also verified that new
> parent.window.Worker().__proto__ yields a different object than invoking new
> window.Worker().__proto__ from the parent page context. So they don't seem
> to be doing the right thing wrt prototype chains either.

Boo.  This stuff is subtle.

> As expected, WebKit is clearly broken with frames, as parent.window.Worker
> does not even yield the same host object that invoking "window.Worker"
> yields from the parent page context (not surprising, since we're looking at
> lexicalGlobalObject() when we shouldn't be).

It might be worth taking this discussion to a bug at this point so as
not to distract everyone on webkit-dev.

Adam