Ionic makes advantage of the Angular life-cycle events. These are the life-cycle events:

• ngOnInit: It is a one-time event that occurs during component initialization. It can be used to set up LOCAL members and make one-time calls to services.
• ngOnDestroy: This event is triggered SHORTLY before the view is destroyed by Angular. It's useful for things like unsubscribing from observables and cleaning up.
• ionViewWillEnter: When the component routing-to is going to animate into view, ionViewWillEnter is invoked.
• ionViewDidEnter: When the component routing-to has done ANIMATING, ionViewDidEnter is fired.
• ionViewWillLeave: When the component routing-from is about to animate, it fires the ionViewWillLeave event.
• ionViewDidLeave: When the component routing-to has done animating, it fires the ionViewDidLeave event.

There are a few more lifecycle events that would prohibit users from GAINING unwanted access.

• ionViewCanEnter: It is called before entering a view, lets you control whether or not the view can be managed by the user.
• ionViewCanLeave: This feature is activated before the user can leave a view and allows you to control whether the view can be left or not.

Routing GUARDS can be used to replace the above two events in Ionic 4.