// /client/src/app/app.service.ts

private tasksSubject = new ReplaySubject<Task[] | null>(1);
private tasks: Task[] = [ {...}, {...} ];

public tasksUpdated$ = Observable<Task[] | null>;

constructor() {
    this.tasksUpdated$ = this.tasksSubject.asObservable();
    this.getAllTasks();
}

private getAllTasks(tasks: Task[]): void {
    this.tasksSubject.next(customer);
}

// /client/src/app/task/task.component.ts
private allTasks: Task[] | null;

private tasksUpdatedSubscription: Subscription;

ngOnInit() {
    this.tasksUpdatedSubscription = this.taskService.tasksUpdated$
                                    .subscribe((tasks: Task[] | null) => {
            this.allTasks = tasks;
    });
}

public ngOnDestroy() {
    this.tasksUpdatedSubscription.unsubscribe();
}