This video, by Rafael Sumitani, introduces the notion of reactive programming. As examples, it uses JavaScript.

References:

https://blog.bitsrc.io/reactive-progr...
https://gist.github.com/staltz/868e7e...
https://en.wikipedia.org/wiki/Reactiv...
https://en.wikipedia.org/wiki/Observe...
https://reactivex.io/intro.html
https://rxjs.dev/guide/overview
   • Intro to Reactive Programming