APIs provided by rxjs/operators

1. filter
2. catchError
3. map
4. mergeMap
5. debounceTime
6. switchMap
7. concatMap
8. mapTo
9. delay
10. tap
11. withLatestFrom
12. repeat
13. takeUntil
14. takeWhile
15. skip
16. concatMapTo
17. toArray
18. bufferCount
19. first
20. throttleTime
21. publish
22. startWith
23. scan