<div>

  <form (ngSubmit)="add()">
    <input type="text" [(ngModel)]="newTodo" name="newTodo" placeholder="New TODO">
    <button type="submit" *ngIf="newTodo" [disabled]="newTodo?.trim().length === 0">Add</button>
  </form>
  <br />
  <ul>
    <li *ngFor="let todo of todos$ | async | pairs" (click)="delete(todo[0])">{{todo[1]}}</li>
  </ul>
  <button (click)="sub()" *ngIf="!todosSub">Log in console</button>
  <button (click)="unsub()" *ngIf="!!todosSub">Stop logging</button>
</div>