Caesar Cipher

caesar_cipher.js

/**
 * Caesar cipher.
 *
 * @link http://en.wikipedia.org/wiki/Caesar_cipher
 * @param {string} msg 
 * @param {number} shift
 * @return {string}
 */
function caesarCipher(msg, shift) { 
    var result  = "", 
        regexp  = /^[a-z]$/i,
        a       = 'a'.charCodeAt(0),
        ch; 
    
    for (var i = 0, len = msg.length; i < len; i++) { 
        ch = msg.charAt(i);
        
        result += (regexp.test(ch))
            ? String.fromCharCode((msg.charCodeAt(i) + shift - a + 26) % 26 + a);
            : ch;
    } 
    
    return result;  
}