【Event: 'drop'】
当达到最大长度时会触发 'drop' 事件，并且这些数据将不会被写入。被丢弃的数据会作为第一个参数传递给事件处理程序。
【The 'drop' event is emitted when to maximal length is reached and that data
will not be written. The data that was dropped is passed as the first argument
to the event handle.】