[TS] Narrow types for Show utility

[calebeby]

Here is part of my code:

<Show when={xScale}>
  {(xScale) => xScale.map(...)}
</Show>

xScale has the type ReadonlySignal<number[] | null>. The parameter xScale has the type number[] | null, but really its type should be number[], since the function won't get called for falsy values.

Within the Show component function, the xScale parameter is known to be truthy, since Show won't run the child unless the signal value is truthy.

Before this PR, I get the TS error 'xScale' is possibly 'null'. from right before the .map.

After this PR, there are no errors, since the xScale parameter excludes falsy types from the original type, so its type is just number[] | null.

I do not use React but if you would like me to make the same change to the react utils package I would be happy to.

Thanks for signals! I have used preact for a long time but this is my first time using signals and it is so neat! I get a smile on my face every time a render is skipped because signals 😄

[changeset-bot]

🦋 Changeset detected

Latest commit: a1e13bf

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@preact/signals	Patch

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[JoviDeCroock]

Thank you! This change can also be done in react if you like.