When should you use useMemo vs useCallback?

• useMemo(fn, deps) caches the result of a computation.
• useCallback(fn, deps) caches the function reference.
  

If you’re memoizing expensive calculations → useMemo.
If you’re passing stable function props to children to avoid re-renders → useCallback.

Example:

const expensive = useMemo(() => calculate(data), [data]); const handleClick = useCallback(() => doSomething(id), [id]);