feat: bind activeElement and pointerLockElement in <svelte:document>

[wackbyte]

Adds support for bind:activeElement and bind:pointerLockElement to <svelte:document>. Closes #2671.

I want to add tests (if necessary, because bind:visibilityState seems to be untested?), but I need some guidance on where exactly they would go.

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🦋 Changeset detected

Latest commit: 92f8b46

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[wackbyte]

Question: The listener fires once when losing or gaining focus, but fires twice when changing focus between two elements (element 1 loses focus, element 2 gains focus). Should it be debounced? Is it feasible to?

[Rich-Harris]

Thank you. We can't use focus and blur events here because they don't bubble; it needs to be focusin and focusout instead. It's finicky to test because JSDOM doesn't do a great job of matching browser behaviour here, so I took the liberty of adding one.

The listener fires once when losing or gaining focus, but fires twice when changing focus between two elements

We can solve this by checking event.relatedTarget in the focusout handler

[wackbyte]

Thank you! focus and blur do seem to work when the listener is capturing, but either way works.

[Rich-Harris]

Ah gotcha, missed the , true and saw it stop working when I refactored to use the listen helper for the sake of code size

[Rich-Harris]

not strictly related to this PR, but a note to self: what is focused? document.focused isn't a thing so this seems odd, maybe a bug? also it'd be nice if these things were sorted alphabetically rather than randomly. will investigate after lunch

[Rich-Harris]

okay, looks like we added focused to all elements a while back. it should probably exclude <svelte:document> and some other things. can look into that as a separate PR

[wackbyte]

JSDOM doesn't implement the pointer lock API as far as I can tell, so I don't think a test can be created for it. I have made sure it works in the REPL, though.

[Rich-Harris]

Yeah, we work around that limitation for fullscreenElement like this...

svelte/packages/svelte/tests/runtime-legacy/samples/document-binding-fullscreen/_config.js

Lines 18 to 23 in f3c291d

	Object.defineProperties(window.document, {
	fullscreenElement: {
	value: div,
	configurable: true
	}
	});

...but it feels like a bit of a pointless test at that point to be honest

[Rich-Harris]

thanks!