Book Image

Mastering JavaScript Functional Programming - Second Edition

By : Federico Kereki
Book Image

Mastering JavaScript Functional Programming - Second Edition

By: Federico Kereki

Overview of this book

Functional programming is a paradigm for developing software with better performance. It helps you write concise and testable code. To help you take your programming skills to the next level, this comprehensive book will assist you in harnessing the capabilities of functional programming with JavaScript and writing highly maintainable and testable web and server apps using functional JavaScript. This second edition is updated and improved to cover features such as transducers, lenses, prisms and various other concepts to help you write efficient programs. By focusing on functional programming, you’ll not only start to write but also to test pure functions, and reduce side effects. The book also specifically allows you to discover techniques for simplifying code and applying recursion for loopless coding. Gradually, you’ll understand how to achieve immutability, implement design patterns, and work with data types for your application, before going on to learn functional reactive programming to handle complex events in your app. Finally, the book will take you through the design patterns that are relevant to functional programming. By the end of this book, you’ll have developed your JavaScript skills and have gained knowledge of the essential functional programming techniques to program effectively.
Table of Contents (17 chapters)
Technical Requirements


1.1. Classes as first-class objects: We learned that functions are first-class objects, but did you know that classes also are? (Though, of course, speaking of classes as objects does sound weird.) Look at the following example and see what makes it tick! Be careful: there's some purposefully weird code in it:

const makeSaluteClass = term =>
class {
constructor(x) {
this.x = x;

salute(y) {
console.log(`${this.x} says "${term}" to ${y}`);

const Spanish = makeSaluteClass("HOLA");
new Spanish("ALFA").salute("BETA");
// ALFA says "HOLA" to BETA

new (makeSaluteClass("HELLO"))("GAMMA").salute("DELTA");
// GAMMA says "HELLO" to DELTA

const fullSalute = (c, x, y) => new c(x).salute(y);
const French = makeSaluteClass("BON JOUR");
fullSalute(French, "EPSILON", "ZETA");

1.2. Factorial errors: Factorials, as we defined them, should only be calculated for non-negative integers; however, the function that we wrote in the Recursion section doesn't verify whether its argument is valid. Can you add the necessary checks? Try to avoid repeated, redundant tests!

1.3. Climbing factorial: Our implementation of a factorial starts by multiplying by n, then by n-1, then n-2, and so on in what we could call a downward fashion. Can you write a new version of the factorial function that will loop upwards?

1.4. Code squeezing: Not that it's a goal in itself, but by using arrow functions and some other JavaScript features, you can shorten newCounter() to half its length. Can you see how?