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

The problem - do something only once

Let's consider a simple, but common situation. You have developed an e-commerce site: the user can fill their shopping cart, and at the end, they must click on a BILL ME button, so their credit card will be charged. However, the user shouldn't click twice (or more) or they would be billed several times.

The HTML part of your application might have something like this, somewhere:

<button id="billButton" onclick="billTheUser(some, sales, data)">Bill me</button>

And, among the scripts you'd have something similar to this:

function billTheUser(some, sales, data) {
    window.alert("Billing the user...");
    // actually bill the user


Assigning the events handler directly in HTML, the way I did it, isn't recommended. Rather, in unobtrusive fashion, you should assign the handler through code. So... Do as I say, not as I do!

This is a very barebones explanation of the problem and your web page, but it's enough for our purposes. Let's now get to think...