Book Image

Mastering JavaScript Functional Programming

By : Federico Kereki
Book Image

Mastering JavaScript Functional Programming

By: Federico Kereki

Overview of this book

Functional programming is a programming paradigm for developing software using functions. Learning to use functional programming is a good way to write more concise code, with greater concurrency and performance. The JavaScript language is particularly suited to functional programming. This book provides comprehensive coverage of the major topics in functional programming with JavaScript to produce shorter, clearer, and testable programs. You’ll delve into functional programming; including writing and testing pure functions, reducing side-effects, and other features to make your applications functional in nature. Specifically, we’ll explore techniques to simplify coding, apply recursion for loopless coding, learn ways to achieve immutability, implement design patterns, and work with data types. By the end of this book, you’ll have developed the JavaScript skills you need to program functional applications with confidence.
Table of Contents (22 chapters)
Title Page
About the Author
About the Reviewer
Customer Feedback
Connecting Functions - Pipelining and Composition
Answers to Questions

Testing - pure versus impure

We have seen how pure functions are conceptually better than impure ones, but we cannot set out on a crusade to vanquish all impurity from our code. First, no one can deny that side effects can be useful, or at least unavoidable: you will need to interact with the DOM or call a web service, and there are no ways to do it in a pure way. So, rather on bemoaning the fact that you have to allow for impurity, try to structure your code so you can isolate the impure functions, and let the rest of your code be the best possible.

With this in mind, you'll have to be able to write unit tests for all kinds of functions, pure or impure. Writing unit tests for functions is different, as to its difficulty and complexity, when you deal with pure or impure functions. While coding tests for the former is usually quite simple and follows a basic pattern, the latter usually require scaffolding and complex setups. So, let's finish this chapter by seeing how to go about testing both...