In this book, we'll cover Functional Programming (FP) in a practical way, though at times we will mention some theoretical points:

Chapter 1, Becoming Functional - Several Questions, discusses FP, gives reasons for its usage, and lists the tools that you'll need to take advantage of the rest of the book.

Chapter 2, Thinking Functionally - A First Example, will provide the first example of FP by considering a common web-related problem and going over several solutions, to finally center on a functional way.

Chapter 3, Starting Out with Functions - A Core Concept, will go over the central concept of FP: functions, and the different options available in JavaScript.

Chapter 4, Behaving Properly - Pure Functions, will consider the concept of purity and pure functions, and show how it leads to simpler coding and easier testing.

Chapter 5, Programming Declaratively - A Better Style, will use simple data structures to show how to produce results working not in an imperative way, but in a declarative fashion.

Chapter 6, Producing Functions - Higher-Order Functions, will deal with higher-order functions, which receive other functions as parameters and produce new functions as results.

Chapter 7, Transforming Functions - Currying and Partial Application, will show some methods for producing new and specialized functions from earlier ones.

Chapter 8, Connecting Functions - Pipelining and Composition, will show the key concepts regarding how to build new functions by joining previously defined ones.

Chapter 9, Designing Functions - Recursion, will show how a key concept in FP, recursion, can be applied to designing algorithms and functions.

Chapter 10, Ensuring Purity - Immutability, will show some tools that can help you work in a pure fashion by providing immutable objects and data structures.

Chapter 11, Implementing Design Patterns - The Functional Way, will show how several popular OOP design patterns are implemented (or not needed!) when you program in FP ways.

Chapter 12, Building Better Containers - Functional Data Types, will show some more high-level functional patterns, introducing types, containers, functors, monads, and several other more advanced FP concepts.

I tried to keep examples simple and down-to-earth, because I wanted to focus on functional aspects and not on the intricacies of this or that problem. Some programming texts are geared toward learning, say, a given framework, and then work on a given problem, seeing how to fully work it out with the chosen tools. (Also, in fact, at the very beginning of planning for this book, I entertained the idea of developing an application that would use all the FP things I had in mind, but there was no way to fit all of that within a single project. Exaggerating a bit, I felt like an MD trying to find a patient on whom to apply all of his medical knowledge and treatments!) So, I opted to show plenty of individual techniques, which can be used in multiple situations. Rather than building a house, I want to show you how to put bricks together, how to wire things up, and so on, so that you will be able to apply whatever you need, as it may fit.

To understand the concepts and code in this book, you don't need much more than a JavaScript environment and a text editor. To be honest, I even developed some of the examples working fully online, with tools such as JSFiddle (at https://jsfiddle.net/) or the like, with absolutely nothing else.

However, you will need some experience with the latest version of JavaScript, because it includes several features that help writing more concise and compact code. We will frequently include pointers to online documentation, such as the documentation available on the MDN (Mozilla Development Network at https://developer.mozilla.org/) to help you get more in-depth knowledge.

This book is geared toward programmers with a good working knowledge of JavaScript, working either on the client-side (browsers) or the server side (Node.JS), who are interested in applying techniques to be able to write better, testable, understandable, and maintainable code. Some background in Computer Science (including, for example, data structures) and good programming practices will also come in handy.

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "Just assign the names of the layers you want to activate to the VK_INSTANCE_LAYERS environment variable".

A block of code is set as follows:

{
 if( (result != VK_SUCCESS) || 
    (extensions_count == 0) ) { 
  std::cout << "Could not enumerate device extensions." << std::endl; 
  return false;
} 

Any command-line input or output is written as follows:

setx VK_INSTANCE_LAYERS VK_LAYER_LUNARG_api_dump;VK_LAYER_LUNARG_core_validation

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Select System info from the Administration panel."

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