Sorry, but why is this type of information is being stored in Javascript? There is no way to keep users from viewing the data. All they would have to do is deactivate Javascript in the browser settings, or use "Save as..." under File, or use one of the other countless options for downloading and saving pages. As a rule you should never trust javascript to hide anything, and never trust any input coming from javascript since it can be manipulated as well. Another realistic problem is that people can catch this data using packet sniffers.
Also, do not trust Javascript encryption. SSL will keep packet sniffers from seeing your code, that can be very trused; but any type of Javascript code encryption will have to send the key along with the encrypted code so that the code can be deciphered on the client. Really, the only solution to your problem is not sending any data to a user that your not fine with them seeing/using. If your not worried about them seeing it but worried about other people use HTTPS.
I would say this over any privacy issue, even if your just trying to hide an email address from spam bots. But wen it comes to merchant ids and passwords you need to be as absolutely careful as possible. When it comes to that type of stuff you open your self to a world of liability, plus you open the door to people who will be likely to try to hack your code.