UseMemo in react

The React useMemo Hook returns a memoized value.

Think of memoization as caching a value so that it does not need to be recalculated.

The useMemo Hook only runs when one of its dependencies update.

This can improve performance.

The useMemo and useCallback Hooks are similar:

useMemo returns a memoized value.

useCallback returns a memoized function.

Learn more about useCallback in the useCallback chapter.

Without useMemo
The useMemo Hook can be used to keep expensive, resource intensive functions from needlessly running.

In this example, we have an expensive function that runs on every render.

When changing the count or adding a todo, you will notice a delay in execution.