An API for asynchronous programming with observable streams. The Observer pattern done right. ReactiveX is a combination of the best ideas from. The Observer pattern, the Iterator pattern, and functional programming. ReactiveX is everywhere, and it's meant for everything. Available for idiomatic Java, Scala, C#, C++, Clojure, JavaScript, Python, Groovy, JRuby, and others. Embrace ReactiveX's asynchronicity, enabling concurrency and implementation independence. Manipulate UI events and API responses, on the Web with RxJS, or on mobile with Rx.NET and RxJava. Avoid intricate stateful programs, using clean input/output functions over observable streams. ReactiveX's operators often reduce what was once an elaborate challenge into a few lines of code. Traditional try/catch is powerless for errors in asynchronous computations, but ReactiveX is equipped with proper mechanisms for handling errors.