code: function has(key) {
          var state = getInternalState(this);
          if (!isObject(key)) return false;
          var data = getWeakData(key);
          if (data === true) return uncaughtFrozenStore(state).has(key);
          return data && $has(data, state.id);
        }
docs: 23.3.3.4 WeakMap.prototype.has(key) 23.4.3.4 WeakSet.prototype.has(value)