Caesar shift in JavaScript and CoffeeScript

In short: I made a Caesar shift in JavaScript and in CoffeeScript.

For small occasions (like month-anniversaries), I like to make little websites for people that only "unlock" on the right day.

Foolproof security would unlock the page with the server, but I don't want to go through all the effort. I just want to prevent people from opening up "View Source" and seeing what I've written, so I wrote a Caesar cipher to obfuscate the text a bit, which will then reverse when I want the page to unlock.

Go check out my JavaScript implementation and my CoffeeScript solution.

Call it like this:

caesarShift('Attack at dawn!',  12);    // Returns "Mffmow mf pmiz!"

And reverse it like this:

caesarShift('Mffmow mf pmiz!', -12);    // Returns "Attack at dawn!"

Easy peasy! Enjoy.