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)

The filter() operator


The filter() operator lets you create a new Observable after omitting some of the data from the original Observable. It receives a function as argument that is called for each element in the original Observable, and it must return an either true or false (actually it can be any truthy or falsy value). If the result of the execution of filterFunction for an object is true, then this object will be propagated; otherwise, it will be omitted.

The filter() operator has the following signature:

observable.filter(filterFunction,[thisContext]); 

The first parameter is mandatory and the second is optional:

  • filterFunction: This is a function that takes an element of the observable as input and returns any truthy or falsy value. If the result of the execution of this function for a given object is true, then this object is propagated; otherwise, it is omitted.
  • thisContext: This is any object to be used as the thisContext of flatMapFunction

We can see an example of the usage of filter...