In Reactive Animations with CSS Variables the subject of RxJS was touched. If you’re not familiar with RxJS, CSS-Tricks has nice introductory article on the subject:
You might have heard of RxJS, or ReactiveX, or reactive programming, or even just functional programming before. These are terms that are becoming more and more prominent when talking about the latest-and-greatest front-end technologies. And if you’re anything like me, you were completely bewildered when you first tried learning about it.