Promises vs Observable

Promise is eager, once they are initialized they trigger the underlying actions and returns the result
Observable is lazy, they don’t trigger until it has a subscriber.

Promises returns only one value
Observable can return multiple values overtime to its subscribers

Promise cannot be canceled, once a promise action is triggered it will execute and return the result
Observable can be canceled, we can call unsubscribe to stop receiving responses from the observable

Promises can be converted to observables, the RxJs library provides a from operator which can convert a promise to an observable. We can use this to deal with some legacy code that is returning promises.

import { from } from 'rxjs';
const myObservable = from(myPromise)

Observable in Angular

Angular internally uses Observables for different features, which needs to listen to specific sources and trigger actions based on specific events/values. Angular uses Observables for the following.