import { fromEvent, Subscription, of } from 'rxjs';
import { map, filter } from 'rxjs/operators';

const dataSource = of(0, 1, 2, 3, 4, 5);
const subscription: Subscription = dataSource.pipe(
  map(value => value * 10),
  filter(value => value > 40)
).subscribe(value => console.log(value));