app.component.ts

import { Component } from '@angular/core';
import { BehaviorSubject } from 'rxjs';

@Component({
  selector: 'my-app',
  template: `
    <p>
      RxJS counter: {{ count$ | async }}
      <button (click)="increment()">+</button>
      <button (click)="decrement()">-</button>
    </p>
  `
})
export class AppComponent  {
  public count$: BehaviorSubject<number> = new BehaviorSubject(0);
 
  public increment(): void {
    this.count$.next( this.count$.getValue() + 1 );
  }

  public decrement(): void {
    this.count$.next( this.count$.getValue() - 1 );
  }
}