Added `untracked` function

[XantreDev]

Resolves https://github.com/preactjs/signals/issues/378

As mentioned in the proposal this allows us to write effects that essentially aren't re-executed by the signals that get accessed in the function body of untracked.

Allowing functionality like

function reaction(sender, listener) {
  effect(() => {
    const value = sender();
    untracked(() => {
      listener(value);
    });
  }
}

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[XantreDev]

@andrewiggins I will be appreciate if you give feedback)

[andrewiggins]

Hey! One question that comes to mind for me is what use case does this help that use const value = signal.peek() doesn't work for?

[XantreDev]

Some reasons is specified in proposal linked to the PR. But shortly: its useful for creating utils that works with callbacks. Most of reactive runtime provides untracked, so it's common pattern, that allows to manipulate reactivity not on sender side, but in consumer side. Yes, I can emulate untracked with computed, but it has too much overhead IMHO.

const untracked = (callback) => computed(callback).peek()

And I am not sure that I can modify values in computed, it feels weird

[andrewiggins]

Oh whoops! I missed the linked proposal. Lemme take a look and mull it over with the team

[XantreDev]

I think this thing are essential for writing Store-like primitives and dealing with it without tricks

[XantreDev]

@andrewiggins when you will return with feedback?

[andrewiggins]

I have some vacation coming up so will be away for a week or two. Though if other core team members have thoughts, no need to block on me

[XantreDev]

@JoviDeCroock what do you think about untracked?

[JoviDeCroock]

This looks good to me, tests seem to be failing and needs a changeset

[XantreDev]

This looks good to me, tests seem to be failing and needs a changeset

Fixed

[betula]

Thanks a lot👍