I create a react-native app using react-redux. Now I need to get my updated data in real-time. I create a function for that, But I can't return my data to yield a call function. when I console.log out my output, It's printed [Function unsubscribe].

export function* getUserData(action) {
    const userID = action.data.userID
    try {
        const userData = yield call(getUserFirebase, userID)
        console.log(userData) //User data can't print:-  [Function unsubscribe]
        if (userData) {
            yield put({
                type: GET_USER_DATA_SUCCESS,
                data: userData
            })
        }
    } catch (error) {
        console.log(error)
        yield put({
            type: GET_USER_DATA_FAILED,
        })
    }

}


function getUserFirebase(userID) {
    const subscriber = firestore()
        .collection('Users')
        .doc(userID)
        .onSnapshot(documentSnapshot => {
            console.log('User data: ', documentSnapshot.data());
            return documentSnapshot.data();
        });

    return () => subscriber();

}