loading.js

const [isLoading, setLoading] = useState(false);
const startLoading = () => setLoading(true);
const stopLoading = () => setLoading(false);

useEffect(() => {
    Router.events.on('routeChangeStart', startLoading);
    Router.events.on('routeChangeComplete', stopLoading);

    return () => {
        Router.events.off('routeChangeStart', startLoading);
        Router.events.off('routeChangeComplete', stopLoading);
    }
}, [])