Angular 6 providedIn - how to customize the @Injectable() provider for dependency injection?

Question

In Angular 5, if I had AbstractClassService and ExtendedClassService that extends the abstract, I could do this in my NgModule\'s providers array:<

Answer 1

I needed to do two things.

First, use implements instead of extends when creating the inheriting class and do not use the providedIn key there:

@Injectable() // removed providedIn
export class ExtendedClassService implements AbstractClassService {}

Second, add the provider instructions to the abstract class instead:

@Injectable({providedIn: 'root', useClass: ExtendedClassService})
export abstract class AbstractClassService {}

Other provider configuration (useValue, useExisting, useFactory) can also be used there.

Credit goes to Abinesh with this comment which led me to the linked blog post. Many thanks to the blog author!