ascii.encode('hoge') === '686f6765';

ascii.js

(function () {
  'use strict';

  var root = this;

  var ascii = {};
  var prevAscii = root.ascii;

  if (typeof exports !== 'undefined') {
    if (typeof module !== 'undefined' && module.exports) {
      exports = module.exports = ascii;
    }
    exports.ascii = ascii;
  } else {
    root.ascii = ascii;
  }

  var chars = function (str) {
    return str.split('');
  };

  var reverse = function (str) {
    return chars(str).reverse().join('');
  };

  var partition = function (str, n) {
    var regex = '(.{' + n + '})|(.+)';
    return str.match(new RegExp(regex, 'g'));
  };

  var rpartition = function (str, n) {
    return partition(reverse(str), n).map(reverse).reverse();
  };

  var repeat = function (str, n) {
    return new Array(n + 1).join(str);
  };

  var ljust = function (str, n, ch) {
    var length = str.length;

    ch = ch || ' ';

    if (length >= n) {
      return str;
    }

    return (repeat(ch, n) + str).slice(-n);
  };

  var zfill = function (str, n) {
    return ljust(str, n, '0');
  };

  ascii.noConflict = function () {
    root.ascii = prevAscii;
    return ascii;
  };

  ascii.encode = function encode(str) {
    var
      index = 0,
      length = str.length,
      concat,
      result = '';

    for (; index < length; ++index) {
      concat = rpartition(str.charCodeAt(index).toString(16), 2);
      concat.forEach(function (str) {
        result += zfill(str, 2).slice(-2);
      });
    }

    return result;
  };

  ascii.decode = function (str) {
    if (typeof str === 'number') {
      str = str.toString(16);
    }

    return partition(str, 2).map(function (element) {
      return String.fromCharCode(parseInt(element, 16));
    }).join('');
  };
}).call(this);