Implement effect cleanups

[jviide]

This pull request implements effect cleanup functions. An effect callback can return a function that's then run the next time the effect either gets rerun or disposed. This pull request also converts the useSignalEffect hook for the Preact and React integrations to use effect cleanups.

The effect(compute: () => void) signature is modified to effect(compute: () => unknown):

const s = signal(0);

const dispose = effect(() => {
  if (s.value === 0) {
    effect(() => () => console.log("hello"));
  } else {
    effect(() => () => console.log("what a"));
  }

  return () => console.log("world");
});

s.value++; // Prints "hello" & "world"
dispose(); // Prints "what a" & "world"

Apart from testing basic functionality, the tests try to cover several corner cases and specific behaviors:

• The cleanup functions of nested effects are run before the parent effect's cleanup.
• When an effect or computed signal is running its nested effect cleanups, and one of the cleanups throws, the rest of the cleanups are still completed and the error is only then thrown upwards.
• If one of effect's nested cleanups throws the effect's own cleanup function still gets called.
• If an effect's own cleanup or one of its nested cleanups throw, the effect becomes essentially disposed. The error is thrown up the stack.
• If a computed signal's nested effects fail when the computed value is being revalidated, all of the computed signal's dependency links are severed. Accessing the computed's value from thereon throws the error.
• If an effect throws an error then its cleanup function is assumed to be undefined.
• Effects can be disposed and retriggered during their own cleanups or nested cleanups.

[changeset-bot]

🦋 Changeset detected

Latest commit: 79ff1e7

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

This PR includes changesets to release 3 packages

Name	Type
@preact/signals-core	Minor
@preact/signals	Minor
@preact/signals-react	Minor

Not sure what this means? Click here to learn what changesets are.

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[github-actions]

Size Change: +454 B (+1%)

Total Size: 67.5 kB

Filename	Size	Change
docs/dist/assets/client.********.js	45.8 kB	+1 B (0%)
docs/dist/assets/index.********.js	1.08 kB	+244 B (+29%)	🚨
docs/dist/assets/signals-core.module.********.js	1.41 kB	+96 B (+7%)	🔍
docs/dist/assets/signals.module.********.js	1.92 kB	+1 B (0%)
docs/dist/basic-********.js	246 B	+2 B (+1%)
docs/dist/demos-********.js	3.35 kB	+4 B (0%)
docs/dist/nesting-********.js	1.13 kB	+1 B (0%)
docs/dist/react-********.js	240 B	+3 B (+1%)
packages/core/dist/signals-core.js	1.46 kB	+104 B (+8%)	🔍
packages/core/dist/signals-core.mjs	1.48 kB	+102 B (+7%)	🔍
packages/preact/dist/signals.js	1.13 kB	-21 B (-2%)
packages/preact/dist/signals.mjs	1.11 kB	-26 B (-2%)
packages/react/dist/signals.js	833 B	-27 B (-3%)
packages/react/dist/signals.mjs	810 B	-30 B (-4%)

ℹ️ View Unchanged

Filename	Size
docs/dist/assets/jsxRuntime.module.********.js	282 B
docs/dist/assets/preact.module.********.js	4 kB
docs/dist/assets/style.********.js	21 B
docs/dist/assets/style.********.css	1.21 kB

_{compressed-size-action}

[marvinhagemeister]

I like that useSignalEffect got a lot simpler!

[marvinhagemeister]

This is awesome!