z.ts

import { Observable } from 'rxjs/Observable';

import 'rxjs/add/observable/interval';

import 'rxjs/add/operator/switchMap';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/mapTo';

Observable.interval(1000)
.switchMap(() => Observable.interval(100))
.subscribe(num => console.log(num));