How to track changes to a variable inside a component?

Question

Angular

1. There is an array inside the component;
2. A new element is added to this array in several different places inside the component (in the createMessage() method and inside the getIncomingMessagesStream() subscriber);
3. Every time a new element is added to the array, you need to perform several actions at once (scroll down the page and some more);
4. Instead of writing additional actions in several places, I want to do it at one point inside the component when a new value is added to my array.
How to do it?

Answer 1

It is possible to throw out data in general in service which to zaprovaydit in the general module for these components.
Well, in the service itself, if on the example of user_id:

@Injectable()
export class DataService {
  private userIdSubject = new Subject<number>();
  $userId = this.userIdSubject.asObservable();

  setUserId(id: number) {
    this.userIdSubject.next(id);
  }
}

In the components themselves, if you need to change the data:
(dataSvc: DataService )
In the components that should track changes and receive data:
(dataSvc: DataService )
And don't forget to subscribe