[malgorithms]

I can answer this for Keybase: first off, it's not because we can't learn other languages (someone suggested that below). In fact, we spent 10 years programming OkCupid in C++, and we've built some high performance projects in Go. It's hard to imagine someone could program anything even remotely like Keybase and lack the programming skills to do it in a variety of languages.

Anyway, in our case we (1) like the async programming model, and actively use it -- on the server side, our services tend to be modular and actually speak over RPC layers to each other, not just one big ugly web process. Node is great at this.

And (2) in this case, because we wanted to have a lot of shared code among our first implementation of a client, our browser front end, and our server. It worked very well to work on all three with one language. It's worked out.

I personally miss compiling C++. :-)

There's a very good chance we'll end up writing a Go client for Keybase. We might switch the official reference client once the functionality is more locked down.

Lastly: it's really CoffeeScript, not JavaScript. Which is a different can of worms to open on here.