We just threw around so many different Node.js version numbers in the previous section that you may have become confused over which version to use. This book is targeting Node.js version 10.x, and it's expected that everything we'll cover is compatible with Node.js 10.x and any subsequent release.

Starting with Node.js 4.x, the Node.js team is following a dual-track approach. The even-numbered releases (4.x, 6.x, 8.x, and so on) are what they're calling Long Term Support (LTS), while the odd-numbered releases (5.x, 7.x, 9.x, and so on) are where current new feature development occurs. While the development branch is kept stable, the LTS releases are positioned as being for production use and will receive updates for several years.

At the time of writing, Node.js 8.x is the current LTS release; Node.js 9.x was just released and will eventually become Node.js 10.x, which in turn will eventually become the LTS release. For complete details about the release schedule, refer to https://github.com/nodejs/LTS/.

A major impact of each new Node.js release, beyond the usual performance improvements and bug fixes, is bringing in the latest V8 JavaScript engine release. In turn, this means bringing in more of the ES-2015/2016/2017 features as the V8 team implements those features. In Node.js 8.x, async/await functions arrived, and in Node.js 10.x support for the standard ES6 module format has arrived.

A practical consideration is whether a new Node.js release will break your code. New language features are always being added as V8 catches up with ECMA Script, and the Node.js team sometimes makes breaking changes in the Node.js API. If you've tested on one Node.js version, will it work on an earlier version? Will a Node.js change break some assumptions we made?

The NPM Package Manager helps us ensure that our packages execute on the correct Node.js version. This means that we can specify in the package.json file, which we'll explore in Chapter 3, Node.js Modules, the compatible Node.js versions for a package.

We can add an entry to package.json as follows:

engines: { 
  "node": ">=6.x" 
} 

This means exactly what it implies—that the given package is compatible with Node.js version 6.x or later.

Of course, your development machine(s) could have several Node.js versions installed. You'll need the version your software is declared to support, plus any later versions you wish to evaluate.