Writing web applications

The flagship use case for Node.js is building web applications. These are inherently event-driven as most or all processing takes place in response to HTTP requests. Also, many websites do little computational heavy-lifting of their own. They tend to perform a lot of I/O operations:

These factors make I/O operations a likely bottleneck for web applications. The non-blocking programming model of Node.js allows web applications to make the most of a single thread. As soon as any of these I/O operations starts, the thread is immediately free to pick up and start processing another request. Processing of each request continues via asynchronous callbacks when I/O operations complete. The processing thread is only kicking off and linking together these operations, never waiting for them to complete. This allows Node.js to handle a much higher rate of requests per thread than other platforms. You can also still make use of multiple threads (for example, on multi-core CPUs) by simply running multiple instances of the Node.js process.

Identifying other use cases

There are of course some applications that don't perform much I/O and are more likely to be CPU bound. Node.js would be less suitable for computationally-intensive applications. Programs that do a lot of processing of in-memory data are less concerned about I/O.

Web applications are not the only I/O-heavy applications though. Other classes of program that could be a good candidate for Node.js include the following:

Node.js is especially suitable for glue applications that pull together functionality from other remote services. The increasing popularity of microservices as an architectural pattern makes this kind of application more common.

Why now?

Node.js has been around for several years, but now is the perfect time to start using it if you haven't already.

The release of Node.js v4 towards the end of 2015 consolidated the project's governance model and heralds Node.js coming to maturity. It also allows the project to keep more up to date with the V8 engine. This means that Node.js can benefit more directly from ongoing development on V8. For example, security and performance improvements to V8 will now make their way into Node.js much sooner.

As discussed earlier in this chapter, the release of the ECMAScript 2015 standard makes JavaScript a much more appealing language. It pulls in useful features from other popular OO languages and resolves a number of long-standing flaws in JavaScript.

Meanwhile, the ecosystem of third party libraries and tools around Node.js and JavaScript continues to grow. Node.js is treated as a first-class citizen by major hosting platforms. Companies such as Google and Microsoft are also throwing their weight behind JavaScript and related technologies.