// Created on savesnippets.com · https://savesnippets.com/WlmcTlYk2gylnj
import { useEffect, useRef } from 'react';

export function usePrevious<T>(value: T): T | undefined {
  const ref = useRef<T | undefined>(undefined);
  useEffect(() => {
    ref.current = value;
  }, [value]);
  return ref.current;
}

// Detect transitions:
function Counter({ count }: { count: number }) {
  const prev = usePrevious(count);
  useEffect(() => {
    if (prev !== undefined && prev !== count) {
      console.log(`changed: ${prev} → ${count}`);
    }
  }, [count, prev]);
  return <span>{count}</span>;
}