import { interval } from 'rxjs';
import { map, withLatestFrom, take } from 'rxjs/operators';

const sportsNews$ = interval(5000).pipe(
  map(i => `Sport News ${i}`)
);

const worldNews$ = interval(1000).pipe(
  map(i => `World News ${i}`)
);

const customizedNews$ = sportsNews$.pipe(
  withLatestFrom(worldNews$),
  map(([sportNews, worldNews]) => `Sport: ${sportNews}; World: ${worldNews}`),
  take(3)
)

customizedNews$.subscribe(console.log);