Why is it so hard to just say, "precompile your code?" Just in time means having to take the same code, and do the same transformations to it, parse and reparse the code, every time you start the app. Yes, React may be a nice templating engine, but why make everyone go through the same process over and over again when you can copy once and not have to worry about it anymore?
The templates are indeed compiled. All the optimisations they describe happens at runtime, when applying changes to the UI. Browser layout engines are complex beasts and writes can be very expensive.
