A BBC navigation bar component broke depending on the external monitor

For anyone who didn't click through to the WebKit bug report the author submitted, a WebKit dev asked him to clarify why the BBC finds it beneficial to be able to detect that the event was sent from a keyboard. This is the author's response:

> Ironically, I want interoperability on this to help with use cases relating to accessibility.

> I work at the BBC and, on our UK website, our navigation bar menu button behaves slightly differently depending on if it is opened with a pointer or keyboard. The click event will always open the menu, but:

> - when opening with a pointer, the focus moves to the menu container.

> - when opening with a keyboard, there is no animation to open the menu and the focus moves to the first link in the menu.

> Often when opening a menu, we don't want a slightly different behaviour around focus and animations depending on if the user 'clicks' with a pointer or keyboard.

> The 'click' event is great when creating user experiences for keyboard users because it is device independent. On keyboards, it is only invoked by Space or Enter key presses. If we were to use the keydown event, we would have to check whether only the the Space or Enter keys were pressed.

Source: https://bugs.webkit.org/show_bug.cgi?id=281430

Does anyone else find this write up confusing?

My understanding from this is that BBC want slightly different behaviour depending on whether it's a mouse or keyboard "click" (keyboard shouldn't show the animation and should focus the first link in the menu).

However, they also want the ease of binding to a single event and while binding to "click" can do this, they have no way to tell whether it was a mouse click or keyboard press which triggered the event.

To solve this they're using an unreliable heuristic after realising in Chrome if the mouse position is screenX=0, screenY=0 it means the event was either triggered by a mouse click at screenX=0, screenY=0 or a keyboard.

As someone whose worked on accessibility projects in the past, this is a really stupid idea imo, and had I reviewed a PR with something like this I would have asked it to be reworked. While I agree browsers should ideally do the same thing, the real issue here seems to me that screenX and screenY make little sense on "click" triggered by a keyboard.

The solution ideally would be a new event ("trigger" or something) which doesn't emit a "MouseEvent", but something more generic which could apply to both a keyboard and mouse event and provide information about the "trigger" source. Imo keyboard "clicks" are weird to begin with and would ideally be fixed with a more appropriate event.

That said, I understand this doesn't currently exist in the spec and a solution is needed now. Therefore I don't see why they couldn't also bind to a "keydown" event then if the click is triggered alongside the "keydown" on the same element, assume it was a keyboard press. That would be far more reliable and far less hacky than what they're doing, and would allow them to trigger from the single event with a bit of extra code to detect if it was a keyboard or mouse.

Hello I am the author and, yes, I totally agree some generic 'trigger' event would be far better.

To use the keydown event means we have to assume that the 'Enter' and 'Space' are the only keys we need to check for. Using 'click' is far safer from an accessibility point of view because it will always respect what your device considers to be some kind of input trigger.

As stated in the UI Events spec:

> For maximum accessibility, content authors are encouraged to use the click event type when defining activation behavior for custom controls, rather than other pointing-device event types such as mousedown or mouseup, which are more device-specific. Though the click event type has its origins in pointer devices (e.g., a mouse), subsequent implementation enhancements have extended it beyond that association, and it can be considered a device-independent event type for element activation.

And to be clear, I would not want to do it this way if it was for some really critical difference in behaviour between pointer or keyboard interactions. I'm OK with this strange mechanism here because the fallback behaviour is not that different. If you're on Safari, for example, which can't check for `screenX === 0`, then all that happens is that there will be an animation when you open the menu.

However, sadly, because of the ways various developers have added to this code over the years, it's broken that fallback behaviour and stopped it working entirely. So I've just finished a refactor to sort that out and it will hopefully be going live soon.