Book Image

Mastering Reactive JavaScript

By : Erich de Souza Oliveira
Book Image

Mastering Reactive JavaScript

By: Erich de Souza Oliveira

Overview of this book

If you’re struggling to handle a large amount of data and don’t know how to improve your code readability, then reactive programming is the right solution for you. It lets you describe how your code behaves when changes happen and makes it easier to deal with real-time data. This book will teach you what reactive programming is, and how you can use it to write better applications. The book starts with the basics of reactive programming, what Reactive Extensions is, and how can you use it in JavaScript along with some reactive code using Bacon. Next, you’ll discover what an Observable and an Observer are and when to use them.You'll also find out how you can query data through operators, and how to use schedulers to react to changes. Moving on, you’ll explore the RxJs API, be introduced to the problem of data traffic (backpressure), and see how you can mitigate it. You’ll also learn about other important operators that can help improve your code readability, and you’ll see how to use transducers to compose operators. At the end of the book, you’ll get hands-on experience of using RxJs, and will create a real-time web chat using RxJs on the client and server, providing you with the complete package to master RxJs.
Table of Contents (11 chapters)

Subscribing to changes (Observer)


To listen to data on an observable, we must call the subscribe() method. This method returns a subscription, which we can use later to stop reacting to the incoming data if we are no longer interested in it.

The subscribe() method of observables has the following signature:

observable.subscribe(onNext,onError,onCompleted); 

All parameters are optional and can be omitted if we are not interested in this type of event:

  • onNext: This is a function to be called every time new data is propagated through the observable
  • onError: This is a function to be called every time an error occurs in the observable
  • onCompleted: This is a function to be called when the observable is completed

The easiest way to subscribe to an observable is to just pass the onNext parameter (as we have been doing in most of our code snippets in this chapter):

Rx.Observable 
    .just('Hello World!!!') 
    .subscribe((message)=>console.log(message)); 

If you run the preceding code, it will print...