code: function _isEnumerable (obj, key) {
      return key in Object(obj) && (_isOwnEnumerable(obj, key) || ~_safeEnumerables(obj).indexOf(key));
  }
docs: Checks whether the specified key is an enumerable property of the given object or not.
  @private
  @param {Object} obj
  @param {String} key
  @returns {Boolean}