It depends. I was working on a websockets based game using node.js on the backend and React, redux & canvas on the front end. As my game grew, more and more cod

It depends. I was working on a websockets based game using node.js on the backend and React, redux & canvas on the front end. As my game grew, more and more code went into the /shared/ folder. It's extremely useful to be able to mirror the game logic that's run on the server for security in the front end for convenience and performance (avoid waiting for round trips for everything). For example, I had a standard RPG style combat system. Being able to share all of the code that does calculations for combat allows you to put those calculations into the UI as much as you want. I think standard CRUD web apps are different because there's much more asymmetry in the responsibilities of the back end and front end.