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 5.x, and it's expected that everything we'll cover is compatible with Node.js 5.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, and so on) are what they're calling Long Term Support (LTS), while the odd numbered releases (5.x, 7.x, and so on) are where current new feature development occurs. While the development branch is kept stable, the LTS releases are more positioned as being more appropriate for production use.
At the time of writing this, Node.js 4.x is the current LTS release; Node.js 6.x was just released and will eventually become the LTS release. Refer to https://github.com/nodejs/LTS/.
It's likely that everything shown in this book will work on 4.x, but that...