855844 - XPConnect bindings get prototype chain wrong.

Status: RESOLVED WONTFIX

(Core :: DOM: Core & HTML, defect)

Description

[Erik Arvidsson]

The following is really broken.

window.HTMLElement = function () {};
console.log(HTMLCanvasElement.prototype instanceof HTMLElement);

it prints true. HTMLCanvasElement.prototype should not change when I change the global HTMLElement.

However, if I first HTMLCanvasElement things work.

HTMLCanvasElement
window.HTMLElement = function () {};
console.log(HTMLCanvasElement.prototype instanceof HTMLElement);

As far as I can tell this only happens with the non Paris bindings.

Comment 1

[Kyle Huey (Exited; not receiving bugmail, old account, do not use)]

What version is this?  I don't see this behavior on trunk.

Comment 2

[Boris Zbarsky [:bzbarsky]]

XPConnect prototypes are lazily created and look up their prototype at creation time.  Which is why order matters for them.

As you noted, this does not happen with WebIDL bindings.  And for the XPConnect ones, it's not going to change.

Note that HTMLCanvasElement should be on WebIDL bindings fairly soon.