Back when i learned about Lighttable years ago i found the instant preview and live editing of running code very cool!

I just realized thats basically what we already do today: i use WebStorm and my webapp hot-reloads any code i type. If i wanted i could even rewind the app state. And when i enable JS debug in IDE its like inception and matrix-view combined, but surprisingly userfriendly still.

To easily try this with just about any IDE check out https://github.com/facebook/create-react-app