I have heard of node.js and have made a couple of services on that. But I'm constrained to stress that node.js is just a small ripple on the server programming environments, currently.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Espruino runs Javascript. Not java.
Js is much more than a front-end language today. Have you ever heard of node.js, for example?