Ionic 4 is built on the Angular framework, and it uses RouterModule, an Angular router module, for navigation. It improves the overall consistency of the application's routing. In previous versions of Ionic, the NavController service was used for navigation, and it is still available, albeit it will be deprecated soon. As a result, it will not be encouraged in new Ionic applications written with Ionic 4.
In the latest revision of Ionic, the ion-router-outlet element is being used to handle the effects that show as the user leaves to or from an element within the application. The ion-router-outlet is identical to the Angular router-outlet, except it has an animation effect added to it.
