text: import {Observable} from 'rxjs/Observable';
  import 'rxjs/add/observable/of';
  import 'rxjs/add/operator/findIndex';
  
  const source$ = Observable.of(3, 1, 4, 1, 5, 9);
  const findIndex$ = source$.findIndex(x => x > 10);
  
  findIndex$.subscribe(
    console.log,
    null,
    () => console.log('complete')
  );
  
  
  