Why is Transport's onclose / onerror / onmessage a property? It can only be listened by one function.

[Areo-Joe]

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Your Question

Why is Transport's onclose / onerror / onmessage a property? It can only be listened by one function.

// ... 
/**
 * Callback for when the connection is closed for any reason.
 *
 * This should be invoked when close() is called as well.
 */
onclose?: () => void;
/**
 * Callback for when an error occurs.
 *
 * Note that errors are not necessarily fatal; they are used for reporting any kind of exceptional condition out of band.
 */
onerror?: (error: Error) => void;
/**
 * Callback for when a message (request or response) is received over the connection.
 */
onmessage?: (message: JSONRPCMessage) => void;
// ... 

I do not understand this decision. I am implementing a custom Transport on server, and I need to listen to the close event too.