Session storage based on session cookies

session-cookie-storage.js

(function() {
  var s = window.sessionCookieStorage = {};

  Object.defineProperty(s, 'length', {
    get: function() { return keys().length; }
  });

  s.key = key;
  function key(index) {
    return keys()[index];
  }

  s.getItem = getItem;
  function getItem(key) {
    return decodeURIComponent(
      document.cookie
        .replace(new RegExp('(?:(?:^|.*;)\\s*' +
            encodeURIComponent(key).replace(/[\-\.\+\*]/g, '\\$&') +
              '\\s*\\=\\s*([^;]*).*$)|^.*$'), '$1'
        )
      ) || null;
  }

  s.setItem = setItem;
  function setItem(key, data) {
    document.cookie = encodeURIComponent(key) + '=' + encodeURIComponent(data);
  }

  s.removeItem = removeItem;
  function removeItem(key) {
    document.cookie = encodeURIComponent(key) +
      '=; expires=Thu, 01 Jan 1970 00:00:00 GMT';
  }

  s.clear = clear;
  function clear() {
    keys().forEach(removeItem);
  }

  function cookies() {
    return document.cookie
      .replace(/((?:^|\s*;)[^\=]+)(?=;|$)|^\s*|\s*(?:\=[^;]*)?(?:\1|$)/g, '')
      .split(/\s*(?:\=[^;]*)?;\s*/)
      .map(decodeURIComponent);
  }

  function keys() {
    return cookies().map(function(c) { return c.split('=')[0]; });
  }
})();