import {useEffect, useRef} from 'react'; export default function usePrevious(value) { // The ref object is a generic container whose current property is mutable ... // ... and can hold any value, similar to an instance property on a class const ref = useRef(null); // Store current value in ref useEffect(() => { ref.current = value; }, [value]); // Only re-run if value changes // Return previous value (happens before update in useEffect above) return ref.current; }