Reactive programming is an asynchronous programming paradigm concerned with data streams and the propagation of change. RxJS (Reactive Extensions for JavaScript) is a library for reactive programming using observables that makes it easier to compose asynchronous or callback-based code. RxJS is a library for composing asynchronous and event-based programs by using observable sequences. It provides one core type, the Observable, satellite types (Observer, Schedulers, Subjects) and operators inspired by Array#extras (map, filter, reduce, every, etc) to allow handling asynchronous events as collections.
RxJS provides an implementation of the Observable type, which is needed until the type becomes part of the language and until browsers support it. The library also provides utility functions for creating and working with observables. These utility functions can be used for:
- Converting existing code for async operations into observables
- Iterating through the values in a stream
- Mapping values to different types
- Filtering streams
- Composing multiple streams
The essential concepts in RxJS which solve async event management are:
- Observable: represents the idea of an invokable collection of future values or events.
- Observer: is a collection of callbacks that knows how to listen to values delivered by the Observable.
- Subscription: represents the execution of an Observable, is primarily useful for cancelling the execution.
- Operators: are pure functions that enable a functional programming style of dealing with collections with operations like map, filter, concat, reduce, etc.
- Subject: is the equivalent to an EventEmitter, and the only way of multicasting a value or event to multiple Observers.
- Schedulers: are centralized dispatchers to control concurrency, allowing us to coordinate when computation happens on e.g. setTimeout or requestAnimationFrame or others.
