In this and many other sections, I'll occasionally run compiled code with Node.js - simply to save us the hassle of building a (demo) website that loads and executes that code.

You can install the Node.js runtime from https://nodejs.org/en (it's available for all operating systems).

This runtime allows you to run JavaScript code right on your system (via the node command) instead of requiring a website.

So when you see me run node app.js (or some other file), that's me using Node.js to execute the code.