小编Eva*_*Jin的帖子

情况 1：在函数组件外部使用 let 变量

https://codepen.io/evan-jin/pen/VwWOPJV?editors=0010

案例2：在父函数组件中使用React.useRef

https://codepen.io/evan-jin/pen/VwWOpvg?editors=0010

情况1

let cursorTimer = null  // << this is the point for 1 case

const Item = ({ num }) => {
    const [hoverItem, setHoverItem] = useState(null)
  
  const addCursor = useCallback(() => {
    clearTimeout(cursorTimer)
    cursorTimer = null
    
    cursorTimer = setTimeout(() => {
      document.body.style.cursor = 'wait'
    }, 10)
  }, [])
  
  const removeCursor =  useCallback(() => {
    if (cursorTimer === null) return
    
    cursorTimer = setTimeout(() => {
      document.body.style.cursor = 'grab'
    }, 500)
  }, [])
  
  useEffect(() …