So I'm a node critic, and I think both the technology and the community suffer from technical immaturity.

But I actually use it and depend on it, for precisely the shared-codebase reason. And it helps immensely for my use case.

I actually started out with Ruby on server side, but spent increasing amounts of time duplicating the same code in both languages. Switching it all to Javascript was a demonstrable win.

When people argue it's a specious benefit, it just means they haven't tried to build a truly ambitious client-side application. If performance, consistency, and security matter you're going to have a lot of code that needs to run at the client for responsiveness and at the server for safety & security. And if you care about offline-capable applications, the problem because even more acute: your clients are now a fully distributed system with their own state, and it's easier to write all the synchronization and recovery logic once, and run it everywhere on both clients and servers.