React 16 Rewrite - What Was the Rewrite Like?

The React 16 release was a pretty vast departure internally from what was previously done. We had found over time that the things that we wanted React to do changed slightly. One of the features we added in React 16 is fragment support where you can return more than one component from your render method. It was actually very difficult to make that happen with our old code base because basically everything assumed that every component would turn into a single node.