If the code/data is confidential, or sensitive, or a security hole, then you can't. Anyone determined enough can figure out what's served to the browser to execute. Code of this nature needs to be run on the server.

If it's just you not wanting to have your code copied and used by others, the method you describe may be enough to deter enough people.

To make it less valuable to others, you could also obfuscate or minify it. I'm sure you can Google for methods and tools for doing that.

/J