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/) and the like, and absolutely nothing else.

In this book, we'll be using ES2019, Node 13, and the code will run on any OS such as Linux, Mac OSX, or Windows; please do check the Technical Requirements section, for some other tools we'll also work with.

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

You can download the example code files for this book from your account at www.packt.com. If you purchased this book elsewhere, you can visit www.packtpub.com/support and register to have the files emailed directly to you.

You can download the code files by following these steps:

1. Log in or register at www.packt.com.
2. Select the Support tab.
3. Click on Code Downloads.
4. Enter the name of the book in the Search box and follow the onscreen instructions.

Once the file is downloaded, please make sure that you unzip or extract the folder using the latest version of:

• WinRAR/7-Zip for Windows
• Zipeg/iZip/UnRarX for Mac
• 7-Zip/PeaZip for Linux

The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/Mastering-JavaScript-Functional-Programming-2nd-Edition-. In case there's an update to the code, it will be updated on the existing GitHub repository.

We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!

There are a number of text conventions used throughout this book.

CodeInText: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: "Let's review our once() function."

A block of code is set as follows:

function newCounter() {
  let count = 0;
  return function() {
    count++;
    return count;
  };
}

const nc = newCounter();
console.log(nc()); // 1
console.log(nc()); // 2
console.log(nc()); // 3

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

function fact(n) {
  if (n === 0) {
    return 1;

  } else {
    return n * fact(n - 1);
  }
}

console.log(fact(5)); // 120

Bold: Indicates a new term, an important word, or words that you see on screen. For example, words in menus or dialog boxes appear in the text like this. Here is an example: "Select the EXPERIMENTAL option to fully enable ES10 support."