ReactQuestion 06

Difference between useMemo and useCallback?

Answer out loud or in your head first, then compare.

Answer

useMemo memoizes a value:

JavaScript

const result = useMemo(() => {
  return expensiveCalculation(data);
}, [data]);

useCallback memoizes a function:

JavaScript

const handleClick =
  useCallback(() => {
    save(id);
  }, [id]);

Remember:

useMemo → result/value

useCallback → function reference

Pitfall:
Don't use them everywhere. They have a cost of their own.

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