Reactive Extensions for JavaScript (RxJS) is a set of libraries created by Matt Podwysocky. Version 4 of the library is maintained and developed by Microsoft. Version 4 can be found at the following link: https://github.com/Reactive-Extensions/RxJS.

Version 5 is a complete rewrite of version 4 and can be found at the following address: https://github.com/ReactiveX/rxjs. Its largest contributor is Ben Lesh, with other notable contributors including Andre Staltz. Version 5 is also Angular's choice of library for handling HTTP, among other things. 

In this chapter, you will learn:

• Which patterns make up RxJS
• The core concepts of RxJS
• How to manually create your own Observables and subscribe to them
• The many ways you can create an Observable
• The importance of managing cleanup
• Understanding what lies beneath by learning to implement the core part of the RxJS library