I think it really depends on the architecture. From my experience (js client <-> HTTP API <-> Express.js <-> Mongo), it never went further than sharing some sma

I think it really depends on the architecture. From my experience (js client <-> HTTP API <-> Express.js <-> Mongo), it never went further than sharing some small bits of code like validation expressions and constants between the client and the server js files. It was just to keep things DRY. I suppose it gets really interessting when you dive into server-side dom manipulation or fully integrated stacks like Meteor.