How does React work 'under the hood'?

So you understand state, props, and components. You are a react dev, and that means you know how to make web applications. However, you might not really know what React does with your code to make your app work. Well, you certainly will after this talk! Not only are we going to give ample treatment to basic questions like 'what is a virtual DOM?', 'How does state trigger a re-render?', but we will live code a simple react-like UI library from scratch.