On Jun 5, 2007, at 10:15 PM, Boris Zbarsky wrote:
Cameron McCormack wrote:
This is probably not what browsers do in practice, though. For
example,
Opera 9 has an addEventListener method directly on the Node interface
prototype object
What Gecko does is to put all properties for all the interfaces an
object implements onto the "closest" prototype object. So if you
have a <div>, HTMLDivElement.prototype will have all the properties
the <div> is supposed to have defined directly on it.
The prototype chain in Gecko basically follows the inheritance model
in the DOM spec: HTMLDivElement.prototype.[[Prototype]] ===
HTMLElement.prototype, etc. Things like EventTarget are off to the
side somewhere as in your imagined way to handle it.
As a result, given a <div> object (call it "div"),
div.[[Prototype]] === HTMLDivElement.prototype
HTMLDivElement.prototype.[[Prototype]] === HTMLElement.prototype
div.appendChild === HTMLDivElement.prototype.appendChild
are all true, while
div.appendChild === HTMLElement.prototype.appendChild
is false.
In WebKit, this would be true.
As a result, to change what the appendChild of a <div> is you have
to change it on HTMLDivElement.prototype.
Generally, we make the same prototype chain you describe, but we put
methods on the JS [[Class]] that defines them. In cases of multiple
interfaces or multiple inheritance, we fold the set of methods into
the next concrete class to inherit from the interfaces.
Of course all of this is subject to change, and in fact is likely to
change some time in the not too distant future.
To be honest, do we really think that specifying the exact prototype
chain is desirable? How likely are UAs to rework the mappings
between their native code and ECMAScript to follow said spec?
If we thought it would improve compatibility we would be open to
changing this for WebKit. Sites hack the prototypes often enough that
we had to add stuff like HTMLElement.prototype to our Window object,
originally we did not have it and the standard is pretty unclear on
whether it should exist.
To give a specific example, it could be a problem that replacing
HTMLElement.prototype.addEventListener will affect <div> elements in
WebKit but not in Gecko, based on what you describe.
Regards,
Maciej
