BFE.devでのAI解答例 - React コーディング問題
5. usePrevious()

import { useEffect, useRef } from 'react';const usePrevious = (value) => {  const ref = useRef();    useEffect(() => {    ref.current = value;  });  return ref.current;};export default usePrevious;

Usage:

import usePrevious from './usePrevious';const MyComponent = () => {  const [count, setCount] = useState(0);  const prevCount = usePrevious(count);  return (    <div>      <p>Current count: {count}</p>      <p>Previous count: {prevCount}</p>      <button onClick={() => setCount(count + 1)}>Increment</button>    </div>  );};