The answer
When passing a function as a prop to a child wrapped in React.memo, so the child does not re-render just because the parent created a new function. Also for handlers used in child effects, to avoid re-running the effect.
useMemo, useCallback, useRef Interview Questions for React
When should you use useCallback in React?
More FAQs in useMemo, useCallback, useRef Interview Questions for React
useMemo memoizes a value; useCallback memoizes a function reference. Use useMemo for expensive computations and useCallback for stable functions passed to memoized children.
useRef returns a mutable object that persists across renders without triggering re-renders. useState triggers a re-render when it changes. Use useRef for DOM references and mutable values that should not drive the UI, and useState for values that should.
For expensive computations that would otherwise run on every render, like sorting a large list. Also to keep an object reference stable for memoized children. Measure first, since memoization is not free.
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