Easy: Write your backend as an API, and let the UI be a thin client that talks to it. You can write your backend in Rails (or Sinatra, which we've used a lot)

Easy: Write your backend as an API, and let the UI be a thin client that talks to it. You can write your backend in Rails (or Sinatra, which we've used a lot) and use the same workflows to wire up models and so forth. I wouldn't want to write database stuff in JavaScript. The frameworks are all terrible. Nobody has managed to replicate the ActiveRecord story for Node.js. Except for legacy stuff (which use Ruby + Sinatra), we write our backends in Go. But that might not be your cup of tea.