您好，我遇到了 userref 問題，我的應(yīng)用程序不斷從我不再訪問的頁面讀取代碼const LandingPage = () => {    useEffect(() => {        document.addEventListener("scroll", () => {            if (window.scrollY < (window.pageYOffset + divRef1.current.getBoundingClientRect().bottom)) {                onHeaderColorSwitch('#c8e9e6')                console.log('green')            } else if (window.scrollY >= (window.pageYOffset + divRef2.current.getBoundingClientRect().top) && window.scrollY < (window.pageYOffset + divRef2.current.getBoundingClientRect().bottom)) {                onHeaderColorSwitch('#ffae5a')            } else if (window.scrollY >= (window.pageYOffset + divRef3.current.getBoundingClientRect().top) && window.scrollY < (window.pageYOffset + divRef3.current.getBoundingClientRect().bottom)) {            }        })    }, [])}我有這個(gè)代碼，但是當(dāng)我使用這個(gè)更改到聯(lián)系頁面時(shí)function App() {    let routes =<Switch>   <Route path="/" exact component={landingPage}/>   <Route path="/contact" exact component={contactPage}/>    </Switch>然后當(dāng)我嘗試滾動(dòng)新頁面時(shí)，我收到此錯(cuò)誤代碼TypeError: Cannot read property 'getBoundingClientRect' of nullHTMLDocument.<anonymous>my-app/src/screens/landingPage.js:22  19 |   20 | useEffect(() => {  21 |     document.addEventListener("scroll", () => {> 22 |         if (window.scrollY < (window.pageYOffset + divRef1.current.getBoundingClientRect().bottom)) {     | ^  23 |             onHeaderColorSwitch('#c8e9e6')  24 |   25 |         } else if (window.scrollY >= (window.pageYOffset + divRef2.current.getBoundingClientRect().top) &&  window.scrollY < (window.pageYOffset + divRef2.current.getBoundingClientRect().bottom)) {即使我現(xiàn)在位于新頁面，事件偵聽器仍在偵聽。一旦刷新頁面，該錯(cuò)誤就不會(huì)影響我，現(xiàn)在和將來如何防止這種情況發(fā)生？