'close' 事件

'close' 事件将在使用 close() 关闭一个 socket 之后触发。 该事件一旦触发，则这个 socket 上将不会触发新的 'message' 事件。

The 'close' event is emitted after a socket is closed with close(). Once triggered, no new 'message' events will be emitted on this socket.