What is Reactive Programming?
Reactive programming is programming paradigm that works with asynchronous data streams.
Data streams can be created from many things such as:
- UI Events
- Http Requests
- File Systems
- Array-like objects
- Memory/Cache
Stream
A sequence of ongoing events ordered in time.
Stream emits a value, error and complete signal.
So we can get the data it emits (any type of data) or we can get errors if something goes wrong
or we can get a signal that notifies when it gets complete.
The image below represents a stream.
Observables:
- Observables are used to watch these streams and emit functions when a value, error or completed signal is returned.
- Observables can be subscribed to by an observer.
- Observables will constantly watch streams and will updated accordingly.
- We can interact with data streams as any regular array.
Simple examples for creating observable
// From one or multiple values
Rx.Observable.of('foo', 'bar');
// From array of values Rx.Observable.from([1,2,3]);
// From an event
Rx.Observable.fromEvent(document.querySelector('button'), 'click');
// From a Promise
Rx.Observable.fromPromise(fetch('/users'));
// From a callback (last argument is a callback)
// fs.exists = (path, cb(exists))
var exists = Rx.Observable.bindCallback(fs.exists);
exists('file.txt').subscribe(exists => console.log('Does file exist?', exists));
Now, we cannot use standard JavaScript ES5 or ES6 to work with Observables and Streams and Reactive Extensions or ReactiveX is what allows us to do that.
Reactive Extension/ReactiveX
- A library for composing asynchronous programs by using observable sequences.
- Provides a long list of operators which allow us to filter, select, combine, and compose observables.
Other Implementations of the Reactive Extensions:
- Rx .NET
- Rx CPP
- RxJava
- Reactive Cocoa
- RxPython
- Reactive-Dart
- Rx.rb (Ruby)
- RxGroovy
- RxSwift
- RxScala
- RxPHP
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