In Angular 5, all the components or directives have specific lifecycle events that are being managed by the @angular/core. They are used in the creation of components, rendering it, creating and rendering their children components in the hierarchy.
These components or directives process changes as and when the multiple data-bound properties have any change, and then destroy them before the removal of their templates from the DOM. Angular 5 provides a specific set of lifecycle hooks, also known as special events that are used to tap into this lifecycle while performing operations when there is a necessity.
In addition, the constructor is used to execute all the prior lifecycle events. Each and every interface comes with a single hook method prefixed with the ng. For example, the ngOnint interface has the Oninit method which needs to be implemented into the component.

BY Best Interview Question ON 13 May 2020