You mean UnityScript. It's not JavaScript!

  Though many in the Unity development community (and even
  in the Unity corporation) refer to UnityScript and 
  JavaScript as if they were equivalent or interchangeable, 
  the two are very different languages. Though they 
  resemble each other syntactically, they have very 
  different semantics.

http://wiki.unity3d.com/index.php/UnityScript_versus_JavaScr...