RxJS v7, v8

rxjs - npm  52M downloads/week!

GitHub - ReactiveX/rxjs: A reactive programming library for JavaScript

RxJS - Introduction
Reactive Extensions Library for JavaScript

RxJS is a library for reactive programming using Observables, to make it easier to compose asynchronous or callback-based code.

Normally you register event listeners.

document.addEventListener('click', () => console.log('Clicked!'));

Using RxJS you create an observable instead.

import { fromEvent } from 'rxjs'; fromEvent(document, 'click').subscribe(() => console.log('Clicked!'));

RxJS with Ben Lesh - Software Engineering Daily

RxJS is an open-source library for composing asynchronous and event-based programs. It provides powerful operators for transforming, filtering, combining, and managing streams of data, from user input and web requests to real-time updates.