How to use the JavaScript language in the unit?

Your information is outdated. Unity used to be compatible with Javascript, through a custom JavaScript variant language called UnityScript. He also used to have a language called Boo. Support for both has been suspended. C # is now the only language that Unity uses for scripts. By default, this is version 3.5 of C #, but 4.6 is an option that you can change through the Player Settings options screen.