For decades, functional programming has been the darling of computer science aficionados, prized for its mathematical purity and puzzling nature that kept it hidden in dusty computer labs occupied by data scientists and PhD hopefuls. But now, it is going through a resurgence, thanks to modern languages such as Python, Julia, Ruby, Clojure and—last but not least—JavaScipt.

JavaScript, you say? The web's scripting language? Yes!

JavaScript has proven to be an important technology that isn't going away for quite a while. This is largely due to the fact that it is capable of being reborn and extended with new frameworks and libraries, such as backbone.js, jQuery, Dojo, underscore.js, and many more. This is directly related to JavaScript's true identity as a functional programming language. An understanding of functional programming with JavaScript will be welcome and useful for a long time for programmers of any skill level.

Why so? Functional programming is very powerful, robust, and elegant. It is useful and efficient on large data structures. It can be very advantageous to use JavaScript—a client-side scripting language, as a functional means to manipulate the DOM, sort API responses or perform other tasks on increasingly complex websites.

In this book, you will learn everything you need to know about functional programming with JavaScript: how to empower your JavaScript web applications with functional programming, how to unlock JavaScript's hidden powers, and how to write better code that is both more powerful and—because it is smaller—easier to maintain, faster to download, and takes less overhead. You will also learn the core concepts of functional programming, how to apply them to JavaScript, how to side-step the caveats and issues that may arise when using JavaScript as a functional language, and how to mix functional programming with object-oriented programming in JavaScript.

But before we begin, let's perform an experiment.