dify-mirror/.agents/skills/vercel-react-best-practices/rules/advanced-use-latest.md

title, impact, impactDescription, tags

title	impact	impactDescription	tags
useLatest for Stable Callback Refs	LOW	prevents effect re-runs	advanced, hooks, useLatest, refs, optimization

useLatest for Stable Callback Refs

Access latest values in callbacks without adding them to dependency arrays. Prevents effect re-runs while avoiding stale closures.

Implementation:

function useLatest<T>(value: T) {
  const ref = useRef(value)
  useLayoutEffect(() => {
    ref.current = value
  }, [value])
  return ref
}

Incorrect (effect re-runs on every callback change):

function SearchInput({ onSearch }: { onSearch: (q: string) => void }) {
  const [query, setQuery] = useState('')

  useEffect(() => {
    const timeout = setTimeout(() => onSearch(query), 300)
    return () => clearTimeout(timeout)
  }, [query, onSearch])
}

Correct (stable effect, fresh callback):

function SearchInput({ onSearch }: { onSearch: (q: string) => void }) {
  const [query, setQuery] = useState('')
  const onSearchRef = useLatest(onSearch)

  useEffect(() => {
    const timeout = setTimeout(() => onSearchRef.current(query), 300)
    return () => clearTimeout(timeout)
  }, [query])
}