JavaScript Fundamentals


JavaScript is arguably the most important programming language on earth. Once thought of as a toy, JavaScript is now the most widely deployed programming language in history. Almost everyone with a computer or a smartphone has all the tools they need to execute JavaScript programs and to create their own.


Although I have used Jetbrains Webstorm , a full Integrated Development Environment (IDE) for JavaScript to develop the source code , All you need is a browser and a text editor.


JavaScript, HTML, and CSS have become so prevalent that many operating systems have adopted the open web standards as the presentation layer for native apps, including Windows 8, Firefox OS, Gnome, and Google’s Chrome OS. Additionally, the iPhone and Android mobile devices support web views that allow them to incorporate Java‐ Script and HTML5 functionality into native applications.


JavaScript is also moving into the hardware world. Projects like Arduino, Tessel, Es‐ pruino, and NodeBots foreshadow a time in the near future where JavaScript could be a common language for embedded systems and robotics. In fact, I have previously blogged about how to get node.js  on the Raspberry Pi.


Creating a JavaScript program is as simple as editing a text file and opening it in the browser. There are no complex development environments to download and install, and no complex IDE to learn. JavaScript is easy to learn, too. The basic syntax is im‐ mediately familiar to any programmer who has been exposed to the C family syntax. No other language can boast a barrier to entry as low as JavaScript’s.


That low barrier to entry is probably the main reason that JavaScript was once widely (perhaps rightly) shunned as a toy. It was mainly used to create UI effects in the browser. That situation has changed.


For a long time, there was no way to save data with JavaScript. If you wanted data to persist, you had to submit a form to a web server and wait for a page refresh. That hindered the process of creating responsive and dynamic web applications. However, in 2000, Microsoft started shipping Ajax technology in Internet Explorer. Soon after, other browsers added support for the XMLHttpRequest object.

Advantages of JavaScript

JavaScript didn’t just luck into its position as the dominant client-side language on the Web. It is actually very well suited to be the language that took over the world. It is one of the most advanced and expressive programming languages developed to date. The following sections outline some of the features you may or may not be familiar with.



Just-in-time compiling: in modern browsers, most JavaScript is compiled, highly opti‐ mized, and executed like native code, so runtime performance is close to that of software written in C or C++. Of course, there is still the overhead of garbage collection and dynamic binding, so it is possible to do certain things faster; however, the difference is generally not worth sweating over until you’ve optimized everything else. With Node.js (a high-performance, evented, server-side JavaScript environment built on Google’s highly optimized V8 JavaScript engine), JavaScript apps are event driven and non‐ blocking, which generally more than makes up for the code execution difference be‐ tween JavaScript and less dynamic languages.



JavaScript has very rich object-oriented (OO) features. The JSON (JavaScript Object Notation) standard used in nearly all modern web applications for both communication and data persistence is a subset of JavaScript’s excellent object-literal notation.

JavaScript uses a prototypal inheritance model. Instead of classes, you have object pro‐ totypes. New objects automatically inherit methods and attributes of their parent object through the prototype chain. It’s possible to modify an object’s prototype at any time, making JavaScript a very flexible, dynamic language.

Prototypal OO is so much more flexible than classical inheritance that it’s possible to mimic Java’s class-based OO and inheritance models in JavaScript virtually feature for feature, and in most cases, with less code. The reverse is not true.

Contrary to common belief, JavaScript supports features like encapsulation, polymor‐ phism, multiple inheritance, and composition.



The JavaScript syntax should be immediately familiar to anybody who has experience with C-family languages, such as C++, Java, C#, and PHP. Part of JavaScript’s popularity is due to its familiarity, though it’s important to understand that JavaScript behaves very differently from all of these under the hood.

JavaScript’s object-literal syntax is so simple, flexible, and concise, it was adapted to become the dominant standard for client/server communication in the form of JSON, which is more compact and flexible than the XML that it replaced.


First-Class Functions

In JavaScript, objects are not a tacked-on afterthought. Nearly everything in JavaScript is an object, including functions. Because of that feature, functions can be used anywhere you might use a variable, including the parameters in function calls. That feature is often used to define anonymous callback functions for asynchronous operations, or to create higher order functions (functions that take other functions as parameters, return a func‐ tion, or both). Higher-order functions are used in the functional programming style to abstract away commonly repeated coding patterns, such as iteration loops or other in‐ struction sets that differ mostly in the variables or data they consume.

Good examples of functional programing include functions like .map(), .reduce(), and .forEach(). The Underscore.js library contains many useful functional utilities. For simplicity, we’ll be making use of Underscore.js in this book.



Inside the browser, everything runs in an event loop. JavaScript coders quickly learn to think in terms of event handlers, and as a result, code from experienced JavaScript developers tends to be well organized and efficient. Operations that might block pro‐ cessing in other languages happen concurrently in JavaScript.
If you click something, you want something to happen instantly. That impatience has led to wonderful advancements in UI design, such as Google Instant and the ground‐ breaking address lookup on The Wilderness Downtown. (“The Wilderness Downtown” is an interactive short film by Chris Milk set to the Arcade Fire song, “We Used To Wait.”

It was built entirely with the latest open web technologies.) Such functionality is powered by Ajax calls that do their thing in the background without slowing down the UI.



JavaScript code, by virtue of its ubiquity, is the most portable, reusable code around. What other language lets you write the same code that runs natively on both the client and the server? (See “Getting Started with Node and Express” on page 125 to learn about an event-driven JavaScript environment that is revolutionizing server-side development.)

JavaScript can be modular and encapsulated, and it is common to see scripts written by six different teams of developers who have never communicated working in harmony on the same page.


The Net Result

JavaScript developers are at the heart of what may be the single biggest revolution in the history of computing: the dawn of the realtime web. Messages pass back and forth across the net, in some cases with each keystroke, or every move of the mouse. We’re writing applications that put desktop application UI’s to shame. Modern JavaScript applications are the most responsive, most socially engaging applications ever written—and if you don’t know JavaScript yet, you’re missing the boat. It’s time to get on board, before you get left behind.

In this series of blog post tutorials I will provide all the essential components to get up to speed with JavaScript, in order to start to gain deeper understanding of one the most most advanced web and mobile programming languages.