port.start()

开始在此 MessagePort 上接收消息。 当将此端口用作事件触发器时，一旦绑定了 'message' 监听器，则会自动调用它

此方法与 Web MessagePort API 相同。 在 Node.js 中，只有在没有事件监听器时才用于忽略消息。 Node.js 在处理 .onmessage 方面也有分歧。 设置它会自动调用 .start()，但取消设置它会让消息排队，直到设置新的处理程序或端口被丢弃。

Starts receiving messages on this MessagePort. When using this port as an event emitter, this is called automatically once 'message' listeners are attached.

This method exists for parity with the Web MessagePort API. In Node.js, it is only useful for ignoring messages when no event listener is present. Node.js also diverges in its handling of .onmessage. Setting it automatically calls .start(), but unsetting it lets messages queue up until a new handler is set or the port is discarded.