Rxjs Behavior Subject for creating observable data.

SomeServiceClass.js

import { BehaviorSubject } from 'rxjs';

export class SomeServiceClass {
  constructor() {
    this.dataObject = new BehaviorSubject('some initial value');
  }
  
  set setData(newData) {
    // notify all subscribed listeners to update data:
    this.dataObject.next(newData);
  }
  
  get getData() {
    return this.dataObject.getValue();
  }
  
  updateData(someNewData) {
    this.setData = someNewData;
  }
}

// In some other class:
class ServiceConsumer {
  constructor(service: SomeServiceClass) {
    this.dataObject = '';
    
    // Whenever the value of the dataObject of our SomeServiceClass is updated,
    // the ServiceConsumer's dataObject will also update:
    this.service.dataObject.subscribe(newDataObject => this.dataObject = newDataObject);
  }
}