interface MessageEvent implements EventType ParametersoptionalT = anyPropertiesreadonlydata: TReturns the data of the message. readonlyorigin: stringReturns the origin of the message, for server-sent events. readonlylastEventId: stringReturns the last event ID string, for server-sent events. readonlysource: nullreadonlyports: ReadonlyArray<MessagePort>Returns transferred ports. variable MessageEventtype{ readonly prototype: MessageEvent; new <T>(type: string, eventInitDict?: MessageEventInit<T>): MessageEvent<T>; }