Comment by Sébastien Portebois on "What are the core differences between promises and observables?"

A very short (and imprecise) answer could be: a promise can be fulfilled once. But an Observable can emit multiple values. In short, it's like an asynchronous (think promise) event emitter.

This graph (you can find similar 4-quadrants graph in many ReactiveX articles) let you compare Promises and Observables: Promise, Observable, Array and values

Observables are really useful (compared to promises) when you have to deal with multiple values, keep - or not - the ordering, and takeUntil really shines. If you're already fluent with promises, have a quick read of The introduction to Reactive Programming you've been missing if a great way to get started with Observables.

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