React.useMemo reference

What is useMemo?

You can use the useMemo hook to memoize the result of an expensive computation. For example, in the snippet below, the computeExpensiveValue function will only execute if a or b has changed since the last render.

const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b])

If you don’t use useMemo, the new value will be computed on every render:

const value = computeExpensiveValue(a, b)

If you don’t provide a dependencies array, the function passed to useMemo will always run on every render – making useMemo useless:

const memoizedValue = useMemo(() => computeExpensiveValue(a, b))

Sources

• useMemo – React docs