port.start()

开始接收此 MessagePort 上的消息。当将此端口用作事件触发器时，一旦附加了 'message' 监听器，就会自动调用此操作。

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

此方法的存在是为了与 Web MessagePort API 保持一致。在 Node.js 中，它仅在没有事件监听器时用于忽略消息。Node.js 在处理 .onmessage 时也有所不同。设置它会自动调用 .start()，但取消设置它会让消息排队，直到设置新的处理器或端口被丢弃。

【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.】