Solution for http://www.codewars.com/dojo/katas/52763db7cffbc6fe8c0007f8

tongues.js

function tongues(code) {
  var vowels = ['a', 'i', 'y', 'e', 'o', 'u'],
    consonants = ['b', 'k', 'x', 'z', 'n', 'h', 'd', 'c', 'w', 'g', 'p', 'v', 'j', 'q', 't', 's', 'r', 'l', 'm', 'f'];
    
  return code.split('').map(function(l) {
    var v = vowels.indexOf(l.toLowerCase()),
      c = consonants.indexOf(l.toLowerCase()),
      letter = l;    
      
    if (v !== -1) {
      letter = vowels[(v-3 < 0) ? ((v-3)+vowels.length)%vowels.length : v-3];
    } else if (c !== -1) {
      letter = consonants[(c-10 < 0) ? ((c-10)+consonants.length)%consonants.length : c-10];
    }
    
    if ((/[A-Z]/).test(l)) letter = letter.toUpperCase();
    
    return letter;
  }).join('');
}