Javascript encyption using a key

I just stumble into this post: http://www.js-x.com/page/javascripts__example.html?view=1109

This is the actual demo of this code: http://utenti.multimania.it/ascii2hex/

Currently the script will not work on other URL except on what you have input during encryption.

I am wondering if it is possible to change this instead of URL to a key. Like the script cannot be decoded if the key is incorrect instead of URL.

Thank you

 

http://www.yuki-onna.co.uk/html/encode.html

 

Thanks to your answer but I need to encode it with key just like in this link: http://utenti.multimania.it/ascii2hex/

Unfortunately it uses URL as its protection.