import { useRef, useEffect } from 'react';

/**
 * 获取上一轮的 props 或 state
 * How to get the previous props or state?
 * https://reactjs.org/docs/hooks-faq.html#how-to-get-the-previous-props-or-state
 * @example
 * ```js
 * function Counter() {
 *   const [count, setCount] = useState(0);
 *   const prevCount = usePrevious(count);
 *   return <h1>Now: {count}, before: {prevCount}</h1>;
 * }
 * ```
 */
export function usePrevious<T>(value: T) {
  const ref = useRef<T>();
  useEffect(() => {
    ref.current = value;
  });
  return ref.current;
}