Observable Promise
1. Used from the library RxJS.
import { Observable } from 'rxjs';		 Built-in API.
2. Can show multiple values using setInterval() method Can resolve only one async task and cannot be used again
3. Can unsubscribe from the observables no longer needed. A promise cannot be canceled.
4. Lazy. Observable is called only when we subscribe. Not lazy.
5. Rich set of operators in the library like map, filter, pipe, retry, etc. No such additional features available
BY Best Interview Question ON 01 Mar 2020