JavaScript is the programming language of the Web. The overwhelming majority of modern websites use JavaScript, and all modern web browsers—on desktops, game consoles, tablets, and smartphones—include JavaScript interpreters, making JavaScript the most ubiquitous programming language in history. JavaScript is part of the triad of technologies that all Web developers must learn: HTML to specify the content of web pages, CSS to specify the presentation of those pages, and JavaScript to specify their behavior. Recently, with the advent of Node (http://nodejs.org), JavaScript has also become an important programming language for web servers.

This book is an excerpt from the more comprehensive JavaScript: The Definitive Guide. No material from the out-of-date second edition remains. I’m hopeful that some readers will find this shorter and denser book more useful than the larger and more intimidating volume from which it came. This pocket reference follows the same basic outline as the larger book: Chapters 1 through 9 cover the core JavaScript language, starting with fundamental matters of language syntax—types, values, variables, operators, statements—and moving on to coverage of JavaScript objects, arrays, functions and classes. These chapters cover the language itself, and are equally relevant to programmers who will use JavaScript in web browsers and programmers who will be using Node on the server-side.