Observable got called twice

[qiluo]

addTodo(newTodo:Todo):Observable {

        let obs = this.todoBackendService.saveTodo(newTodo);

        obs.subscribe(
                res => {
                    this._todos.next(this._todos.getValue().push(newTodo));
                });

        return obs;
}

obs would get called twice, since there are two subscribers (inner and outer of addTodo method), may have to change it to let obs = this.todoBackendService.saveTodo(newTodo).share();

[markonyango]

Just out of curiosity, why does one need an observable here at all?