以下为ChatGPT自动生成的解答，正确与否请自行判断。

BFE.devAI解答 - React 代码题
5. usePrevious()

import { useEffect, useRef } from "react";

function usePrevious(value) { const ref = useRef();

useEffect(() => { ref.current = value; }, [value]);

return ref.current; }

export default usePrevious;

// Usage: // const prevValue = usePrevious(value); // Where value is the current value you want to track the previous value of.

BFE.devAI解答 - React 代码题5. usePrevious()