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


1.1. Classes as first-class objects: We saw that functions are first class objects, but did you know classes also are? (Though, of course, speaking of classes as objects does sound weird...) Study this 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");
      // EPSILON says "BON JOUR" to ZETA

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

1.3. Climbing factorial: Our implementation of factorial starts 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?