Question 1

What does useCallback do?

Accepted Answer

Returns a memoized callback that changes only when deps change. Useful when passing functions to memoized children or as effect deps. Not free—has its own cost.

Question 2

useCallback vs useMemo for functions?

Accepted Answer

useCallback(fn, deps) ≡ useMemo(() => fn, deps); prefer useCallback for readability. Same underlying idea: stable function identity.

Question 3

When does useCallback actually help?

Accepted Answer

When a child is React.memo and would re-render from new function props, or when used in dependency arrays. Without memoized consumers, useCallback often does nothing useful.

Question 4

Stale closure bugs with useCallback?

Accepted Answer

Missing deps capture old state; over-empty deps are a common trap. Use functional setState or refs for latest values when intentionally stabilizing callbacks.

Question 5

Refactor: child re-renders every parent keystroke due to inline handlers. Options?

Accepted Answer

Memoize child + useCallback, lift less state, or split components so inputs don't rerender heavy trees. Often component split beats memo theater.

useCallback React Interview Questions

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