ROT(13|47) の実装、変数の名前とかてけとー。

rot-n.js

var rot = (function () {
  function tr(str, from, to) {
    return str.replace(new RegExp('[' + from + ']', 'g'), function (key) {
      return to[from.indexOf(key)] || key;
    });
  }

  function range(min, max) {
    var result = '';

    min = min.charCodeAt(0);
    max = max.charCodeAt(0);

    for (; min <= max; min++) {
      result += String.fromCharCode(min);
    }

    return result;
  }

  var _rot13 = {
    from: range('A', 'Z') + range('a', 'z'),
    to: range('N', 'Z') + range('A', 'M') + 
        range('n', 'z') + range('a', 'm')
  };

  function rot13(str) {
    return tr(str, _rot13.from, _rot13.to);
  }

  var _rot47 = {
    from: range('!', '~'),
    to: range('P', '~') + range('!', 'O')
  };

  function rot47(str) {
    return tr(str, _rot47.from, _rot47.to);
  }

  return {
    rot13: rot13,
    rot47: rot47
  };
})();