What principle distinguishes useMemo from useCallback in React?

The main difference between useMemo and useCallback in React is:

• useMemo memoizes the value returned by a function.
• useCallback memoizes the function itself, returning it.

That is, useMemo is used when you need to remember the result of a computation (for example, a complex calculation) so that it is not recalculated on every render, while useCallback is used when you need to keep a reference to a function to avoid recreating it, which is important when passing functions to child components or optimizing with React.memo.

Example:

const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);
const memoizedCallback = useCallback(() => doSomething(a), [a]);

Thus, useMemo returns a value, and useCallback returns a function.