Observables Promises
These are used for streams of events over time. It is able to handle only one event.
It supports operators such as map, filter, reduces, etc., and is cancel-able and retry-able. It is not easy to handle and returns a single value.
It provides chaining and subscriptions for handling complex applications. It uses only the .then() clause.
Here the subscribe method is used for a centralized and predictable error handling. It pushes the errors to the child's promises.

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BY Best Interview Question ON 29 Jun 2020