Compose: Support React 19 ref callback cleanups in useMergeRefs#78685
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tyxla wants to merge 2 commits into
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Compose: Support React 19 ref callback cleanups in useMergeRefs#78685tyxla wants to merge 2 commits into
useMergeRefs#78685tyxla wants to merge 2 commits into
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tyxla
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useMergeRefs
jsnajdr
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May 26, 2026
| cleanup(); | ||
| } else { | ||
| assignRef( previousRef, null ); | ||
| } |
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This snipped that does cleanup could be extracted into a detachRef function, similar to assignRef. Currently we duplicate the code twice.
| } else { | ||
| currentRefsRef.current.forEach( ( ref, index ) => { | ||
| cleanupsRef.current[ index ] = assignRef( ref, value ); | ||
| } ); |
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What if the result of useMergeRefs was a function that returns a cleanup callback, i.e., the most modern thing? Currently it's still the old function that accepts T | null and returns void.
It wouldn't be usable for React 18 code, but is that a concern?
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What
useMergeRefsnow honors the React 19 ref callback cleanup pattern. If an inner ref callback returns a function, that function is invoked at teardown (node change, dependency change, or unmount) instead of the callback being called withnull. Callbacks that don't return a cleanup keep the existingnull-pass behavior, so this is purely additive and none of the 132 call sites need to change.Why
Updating
useMergeRefsto support React 19 ref callback cleanups.This is a prerequisite for deprecating
useRefEffectin favor of nativeuseCallbackref cleanups, because onceuseRefEffectis gone, every migrated call site becomes a plainuseCallbackwhose body returns a cleanup, anduseMergeRefsis the consumer that has to honor it.Part of #71336.
How
assignRefnow returns the function ref's return value (typed() => void | undefined). Object refs continue to set.currentand returnundefined.cleanupsRefstores the cleanup returned by each inner ref.nullpath;useLayoutEffectdep-change path) prefer the stored cleanup over calling the ref withnull.nullbyuseMergeRefs. This matches React 19's own behavior for native refs.useRefEffectto the React 19-nativeuseCallbackpattern.Out of scope:
useRefEffectsource, tests, and call sites, untouched. That's the next checkbox.useMergeRefscall sites, none of their behavior changes.Testing instructions
npm run test:unit -- packages/compose/src/hooks/use-merge-refs, 14 tests pass (7 existing, regression-protected; 7 new for the cleanup path).