code: function guid() {
      function _s4() {
          return Math.floor(
              (1 + Math.random()) * 0x10000
          ).toString(16).substring(1);
      }
      return _s4() + _s4() + '-' + _s4() + '-' + _s4() + '-' + _s4() + '-' + _s4() + _s4() + _s4();
  }
docs: Generate unique id
  @source http://stackoverflow.com/questions/105034/create-guid-uuid-in-javascript#105074
  @returns {string}