CODE EXAMPLE FOR JAVASCRIPT

Using useEffect with async

useFocusEffect(
    useCallback(() => {
        let dbRef;
        let didCleanup = false;
        (async() => {
            try {
                const user = JSON.parse(await AsyncStorage.getItem("user"));

                if (!didCleanup && user.uid) {
                    dbRef = ref(dbDatabase, "/activity/" + user.uid);

                    onValue(query(dbRef, limitToLast(20)), (snapshot) => {
                        console.log(snapshot.val());
                    });
                }
            } catch (error) {
                // ...handle/report the error...
            }
        })();
        return () => {
            didCleanup = true;
            if (dbRef) {
                off(dbRef);
            }
        };
    }, [])
);