RxJS is very cool and well designed, and stands on its own. Worth learning about even if you don't use Angular, but definitely if you do! The basics are easy to understand, but there are a whole lot of deep profound operators that it will take a long time to master, although you don't need them all at first.

https://rxjs-dev.firebaseapp.com/api

Reading the guide and pondering the following table helped me understand how other mechanisms in JavaScript work together and relate to each other, and the corner that Observable occupies:

https://rxjs-dev.firebaseapp.com/guide/observable

>Observables are lazy Push collections of multiple values. They fill the missing spot in the following table:

            SINGLE      MULTIPLE
    Pull:   Function    Iterator
    Push:   Promise     Observable