rot13.js

function rot13(message) {
    return message.replace(/[A-Za-z]/g, function(input){
        var charCode = input.charCodeAt(0);
        var start = charCode <= 'Z' ? 65 : 97;
        charCode = (charCode - start + 13) % 26 + start;
        return String.fromCharCode(charCode);
    });
}