需要在 transferList 参数中显式列出的对象在传给 postMessage() 调用的对象中，但未在 transferList 中为该调用提供。
通常，这是 MessagePort。
An object that needs to be explicitly listed in the transferList argument
is in the object passed to a postMessage() call, but is not provided
in the transferList for that call. Usually, this is a MessagePort.