Evan Hahn - Express in Action: Writing, building, and testing Node.js applications

Before we talk about Express, we need to talk about Node.js.

For most of its life, the JavaScript programming language has lived inside of web browsers. It started as a simple scripting language for modifying small details of webpages, but grew into a complex language, with loads of applications and libraries. Many browser vendors like Mozilla and Google began to pump lots of resources into fast JavaScript runtimes, and Google Chrome and Mozilla Firefox got much faster JavaScript engines as a result.

In 2009, Node.js came around. Node took V8, Google Chrome's powerful JavaScript engine, out of the browser and made it able to run on servers. In the browser, developers had no choice but to choose JavaScript. In addition to Ruby, Python, C#, Java, or other languages, developers could now choose JavaScript when developing server-side applications.

JavaScript might not be the perfect language for everyone, but Node.js had some real benefits. For one, the V8 JavaScript engine is fast, and Node encourages an asynchronous coding style, making for faster code while avoiding multi-threaded nightmares. JavaScript also had a bevy of useful libraries because of its popularity. But the biggest benefit of Node.js is the ability to share code between browser and server. Developers don't have to do any kind of context switch when switching between client and server. Now they can use the same code and the same coding paradigms between two different JavaScript runtimes; the browser and the server.

Node.js caught onpeople thought it was pretty cool .

Like browser-based JavaScript, Node.js provides a bevy of low-level features you'd need to build an application. But like browser-based JavaScript, its low-level offerins can be a bit verbose and difficult.

Enter Express.js. Express is a framework that acts as light layer on top of the Node.js web server, making it more pleasant to develop Node.js web applications.

Express.js is philosophically similar to jQuery. People want to add dynamic content to their webpages, but the vanilla browser APIs can be verbose, confusing, and limited in features. Developers often have to write a lot of boilerplate code. jQuery exists to cut down on this boilerplate code by simplifying the APIs of the browser and adding helpful new features. That's basically it.

Express is exactly the same. People want to make web applications with Node.js, but the vanilla Node.js APIs can be verbose, confusing, and limited in features. Developers often have to write a lot of boilerplate code. Express exists to cut down on this boilerplate code by simplifying the APIs of Node.js and adding helpful new features. That's basically it!

Like jQuery, Express aims to be extensible. It's hands-off about most parts of your applications' decisions and is easily extended with third-party libraries. Throughout this book and your Express career, you'll have to make decisions about your applications' architectures and you'll extend Express with a bevy of powerful third-party modules.

You probably didn't pick up this book for the in short definition, though. The rest of this chapter (and book, really) will discuss Express in much more depth.

NOTE This book assumes that you are proficient in JavaScript, but not Node.js.

Node.js is no child's play.

When I first started using Node.js, I was confused. What is it?

Node.js (often shortened to "Node") is just a JavaScript platform a way to run JavaScript. Most of the time, JavaScript is run in web browsers. But there's nothing about the JavaScript language that requires it to be run in a browser. It's a programming language just like Ruby or Python or C++ or PHP or Java. Sure, there are JavaScript runtimes bundled with all popular web browsers, but that doesn't mean that it has to be run there. If you were running a Python file called myfile.py, you would run python myfile.py . But you could write your own Python interpreter, call it SnakeWoman, and run