Everything happens on client-side the server is just for saving sessions and file serving. So technically its not written in node.js. Node is only a dependency

Everything happens on client-side the server is just for saving sessions and file serving. So technically its not written in node.js. Node is only a dependency for the development tools we use (coffee-script, mini-server for development). However the server running repl.it is written in Node, its nothing fancy but it makes us run cheap and it will be open-sourced soon.