As you can read on the JavaScript page, it is a ScriptingLanguage that despite common believe doesn't only run in WebBrowsers. There have always been server-side JavaScript interpreters (simply the CommandLine interpreters run as CGI script processors), some sort of "low-end JavaServerPages scripts" if you want.
Also it can be useful and is used as embedded ScriptingLanguage in a few high end ContentManagementSystems (as module glue and low speed application logic or so).
Node.js is a good example of server-side JS http://nodejs.org/
http://www.infoworld.com/d/application-development/javascript-conquers-the-server-969
This suggests that it may become a common server-side language because developers have to learn it anyhow for the client-side. Having it server-side means mastering fewer languages.