port.close()

禁止连接双方进一步发送消息。
当不再通过此 MessagePort 进行通信时，可以调用此方法。

【Disables further sending of messages on either side of the connection. This method can be called when no further communication will happen over this MessagePort.】

'close' 事件 会在通道中属于的两个 MessagePort 实例上触发。

【The 'close' event is emitted on both MessagePort instances that are part of the channel.】