In Angular 2, the Safe navigation operator can be used to prevent errors while trying to access the object properties of non-existent objects.
Here’s an example explaining the above statement:

{{ phone?.number }}

This above line of code only evaluates the number when the phone is not null or undefined. This is very suitable in situations where a phone is something that is loading asynchronously.

BY Best Interview Question ON 23 Feb 2020

Example

class PageTest {
   public key = true;
}
@Component({
   moduleId: module.id,
   selector: 'elvis-test',
   templateUrl: 'elvis-test.html'
})
export class ElvisTestComp {
   @Input() elvisTest?: PageTest;
}

<div>{{elvisTest?.key}}</div>