void initMessageEvent(
    in DOMString typeArg,
    in boolean canBubbleArg,
    in boolean cancelableArg,
    in SerializedScriptValue dataArg,
    in DOMString originArg,
    in DOMString lastEventIdArg,
    in DOMWindow sourceArg,
    in Array messagePorts); 

readonly attribute SerializedScriptValue data; 

readonly attribute DOMString lastEventId; 

readonly attribute DOMString origin; 

readonly attribute Array ports; 

readonly attribute DOMWindow source;