Most likely they have headless web browsers running on both the main spacecraft (probably chromium) and the Philae lander. Web sockets enables the lander to communicate to the spacecraft which then sends its signals down to earth using regular HTTP (you don't want to keep an interstellar HTTP connection open). All of it is of course written in JavaScript, more specifically vanilla-JavaScript - which frankly I find weird given that I'd hope they would use a framework such as socket.io - bad engineering if you ask me. The lander obviously uses latest Node.js and npm to update some of its modules which are again sent across the wire using interstellar HTTP.