Is it possible to have abstract classes in Unity/JS in more than just concept? I try abstract class fooClass {} and get nothing but anger from the debugger.
In Unity: yes, through C#. In JS: i guess you found out you can’t :P.
There are several programming features that you can use in C# that are not supported for JS. If you really want to use these, you will need to switch language.
UnityScript is of interest if you want to do something fast and/or simple. That make it especially interesting for beginners and artists, people without a programming background.
If you need complexity and a fullscale programming language, then C# is the language to use.