fix(useAsyncEffect): call cleanup when component unmounts before async effect resolves

[eunwoo-levi]

Overview

useAsyncEffect drops the cleanup function when the component unmounts before the Promise resolves.

Root Cause

cleanup is assigned inside .then(), but React's cleanup runs synchronously on unmount.
If unmount fires before the Promise resolves, cleanup is still undefined — the user's cleanup function is permanently lost.

effect().then(result => {
  cleanup = result; // assigned asynchronously
});                                                                                       

return () => {                                                                            
  cleanup?.(); // undefined if unmount happens first → no-op
};

Fix

Added an isCleaned flag. If unmount fires before the Promise resolves, the cleanup is called immediately after the Promise settles.

effect().then(result => {
  cleanup = result;
  if (isCleaned) {                                                                        
    cleanup?.();
  }                                                                                       
});             

return () => {
  isCleaned = true;
  cleanup?.();
};

Changes

• useAsyncEffect.ts — add isCleaned flag
• useAsyncEffect.spec.ts — add missing test case: unmount before Promise resolves

Checklist

• Did you write the test code?
• Have you run yarn run fix to format and lint the code and docs?
• Have you run yarn run test:coverage to make sure there is no uncovered line?
• Did you write the JSDoc?

[Copilot]

Pull request overview

Fixes useAsyncEffect so that a cleanup function returned from an async effect is still executed even if the component unmounts (or deps change) before the promise resolves.

Changes:

• Track an isCleaned flag to ensure late-resolving cleanup functions are invoked after unmount.
• Add a regression test covering “unmount before promise resolves”.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
packages/core/src/hooks/useAsyncEffect/useAsyncEffect.ts	Ensures async-provided cleanup still runs if unmount happens before the promise settles.
packages/core/src/hooks/useAsyncEffect/useAsyncEffect.spec.ts	Adds a regression test for early unmount with delayed async resolution.