import { TimerObservable } from 'rxjs/observable/TimerObservable';
import 'rxjs/add/operator/take';

countdown = TimerObservable.create(0, 1000).take(6);

startCountdownTimer(): void {
    this.countdown.subscribe(
        i => this.timeRemaining = (5 - i).toString(),
        null,
        () => this.toDelete = -1)
}

cancelCountdownTimer(): void {
    this.countdown.unsubscribe();
}