Reaction is a great example of just how far you can go with JavaScript. Remember the humble but proud JavaScript tip calculator in the Beginner’s section? Well, Reaction raises the stakes from a JavaScript project that helps with one specific kind of transaction, to a JavaScript project that allows users to run an entire business. Reaction is a commerce platform used for managing business in real time and delivering shopping experiences directly to customers. And it’s open source, meaning you can study how it all works!