Add a useSignalEffect implementation that behaves like useEffect

[DAreRodz]

The current useSignalEffect hook implementation from @preact/signals calls the passed callback before changes to the DOM are made, but it should wait for DOM changes (like useEffect does).

I just copy-pasted the useSignalEffect hook and its dependencies from preactjs/signals#290 until those changes are merged and released in @preact/signals.

[luisherranz]

I've been trying to add tests to reproduce the problem here and to reproduce that I needed a newer version of wp-show that actually removes the elements from the DOM. So I added it, but then the tests of wp-show where not passing because the new createTreeWalker algorithm doesn't support templates, so I started adding support for that. That part of the code is still a mess and I'm not even sure if it works, so I'll keep working on that on Monday, or I'll remove the code and I'll skip the test until we add this in another PR.

The good news is that the new useSignalEffect passes the tests and the older one doesn't so it's an improvement 🙂

[luisherranz]

I couldn't use data-wp-bind.hidden because then the test that checks that effects are removed when the DOM element is removed fails, but it turns out that the tests pass with the current implementation of wp-show as well.

This should be ready now. As you started the PR, I've preapproved it. Feel free to review and merge 🙂

[luisherranz]

Oh, the tests pass on my computer but not here. I don't know what's going on.

[luisherranz]

Well, I ended up:

• Adding a temporary fake wp-show directive that removes things from the DOM because the other was failing in webkit.
• Testing if something was added to the DOM with state and an element instead of checking a value in window because it was a bit flaky.

Things should be ready now.

[DAreRodz]

Thanks @luisherranz! The changes you did look great to me. 😄

[DAreRodz]

This return is not needed; I'm pretty sure event listener callbacks always return undefined (see this). I'll change this, don't worry. 🙂

[luisherranz]

Oh, I see. So instead of returning false in the onclick attribute, you'd use event.stopPropagation() in the event listener. And Preact is using the listener, not the attribute, right?