The first and foremost advantage of Node.js is JavaScript. If you know and code in JavaScript regularly, you already know most of Node.js; all that's left to learn can be thought of as APIs and best practices.

Node.js—built over Google Chrome's V8 JavaScript engine—allows entire applications to be written using JavaScript. We have already been writing frontends in JavaScript; with Node.js, we write the backend as well, in the same language that we have honed our skills on and grown to love. It saves every frontend developer from learning one more language or relying on some other developer to expose the RESTful APIs required by their application.

Node.js was designed around events and callbacks. As a JavaScript developer, you would already be familiar with the concept of listening to events and using callbacks. Node.js incorporates this philosophy in each and every aspect of the platform. Be it in server request handling, I/O, or database interactions, everything in Node.js will ideally be handled by a callback attached to an event by a listener.

This brings us to one of the most important concepts behind Node.js, that is, the event loop. I like the fast food restaurant analogy by Dan York (http://code.danyork.com) for explaining event loop-based systems.

Consider a restaurant where you go to the cashier, place your order, and wait till your food is ready. In this case, the cashier cannot serve the other customers till you have your order, and the queue is blocked. If the restaurant has a large inflow of customers and needs to scale up, they will have to invest in hiring more number of cashiers, creating more cash counters, and so on. This is similar to the traditional multithreading model.

In contrast, let us see the model many other restaurants use. In this case, you go to the cashier and place your order (which he/she hands over to the kitchen); he/she then accepts your payment and gives you a token. You then step aside, and the cashier moves on to the next customer. When your order is ready, the kitchen server announces this by calling your name or flashing your token number, and you walk up and fetch your order. This event-oriented approach optimizes the work of the cashier and lets you wait on the side, freeing up the relevant resources to service others until your work is done.

In Node.js, the server is the cashier, and all the handlers are the kitchen crew. The server accepts a request and spins it off to a handler. It then moves on to accept other requests. When the request is processed and the results are in place, the response is queued on the server and sent back to the client when it reaches the front of the queue.

As opposed to the traditional approach of launching the threads or processes of the server (which is similar to adding more cashiers), this method is more efficient, as the workers launched have dedicated responsibilities. This is much lighter and cheaper than replicating the entire server.

In the sections ahead, we will see that we register the handlers or the workers with the server to handle certain requests, and all the server does is delegate the requests to these workers.

The advantage of the event-driven design is that everything we design is non-blocking. "You don't wait on me, I call you" is the mantra that relieves us from the pain involved in waiting on a request to be fulfilled. It frees up the system resources that would have otherwise been spent in waiting on the request, so that they can be used for the other tasks in the queue. This allows the Node.js applications to give a very high performance and capability of handling a very high load.

Node.js is a modular framework with a modern module system from the ground up. Everything in Node.js is built as modules running in the V8 JavaScript engine. Every functionality in the platform is provided by means of modules. This keeps the platform lean and brings in only that what is required. Having a native module system also helps in keeping our applications modular.

JavaScript has become one of the most widely-used languages in the past few years and has a vibrant community. Node.js provides developers with a good platform that assists them in developing end-to-end applications in JavaScript. Node.js has also brought in many revolutionary concepts, namely, always asynchronous, non-blocking I/O, event-oriented servers, and so on. This has resulted in a very vibrant, large, and active community. New modules are coming up continuously, and the community provides active support and is very helpful. Most of the popular modules and frameworks built for Node.js generally come from the community and are mostly open source.

Many companies have invested heavily in Node.js in the past couple of years. From Ryan Dahl's employer, Joyent, to the creators of the Mojito framework (Internet giant Yahoo!), many companies have built products, platforms, frameworks, and services around Node.js. This kind of corporate commitment assures a stable future.