const customIntervalObservable = Observable.create(observer => {
        let count = 0;
        setInterval( () => {
          observer.next(count);
          if(count == 2){
              observer.complete();
          }
          if(count > 3){
              observer.error(new Error('Count is greater than 3!'));
          }
          count++;
        }, 1000)}
);

this.firstObsSubscription = customIntervalObservable.subscribe(
        data => {
          console.log(data);
        },
        error => {
          console.log(error);
        },
        () => {
          console.log('completed')
        }
);