如何将基于类的生命周期方法转换为函数式方法？

Question

In the following code:

  componentDidMount() {
    registerForPushNotificationsAsync();
    this._notificationSubscription = Notifications.addListener(this._handleNotification);
  }

what's the difference between assigning Notifications.addListener(this._handleNotification); to this._notificationSubscription and simply going:

  componentDidMount() {
    registerForPushNotificationsAsync();
    Notifications.addListener(this._handleNotification);
  }

Also, how do you convert it into a functional component format like the following?

    useEffect(() => {
        registerForPushNotificationsAsync();
        Notifications.addListener(handleNotification);
    }, []);

Answer 1

useEffect(() => {
        registerForPushNotificationsAsync();
        const subscription =Notifications.addListener(handleNotification);
        return () => {
            // Call method for clear subscription. I asume that it is remove but it can be another
            subscription.remove()
        }
    }, []);