If you use either Sproutcore or Cappuccino for your frontend, doesn't it mean that everyone could see your javascript and copy it?
If so, they'll have your whole frontend code.
Am I right or wrong?
You are right. The javascript in your web pages runs on the client - so it needs to be downloadable by the client. By definition, clients have 'your whole frontent code'.
The usual process of trying to make your javascript hard to read (and therefore copy) is called obfuscation. Obfuscated javascript is the same as non-obfuscated javascript to the browser - so it will work equally well with any javascript framework.