Handling Callback Variables

With Javascript applications that make asynchronous Ajax requests, does it make sense to store a global variable that indicates the callback that should be executed? That is, depending on the current state of the application, a different callback function may need to execute for the same API call. Should a global variable be set before the request is made and checked each time by the response?

That doesn't feel right to me. Neither does sending application data along with the API request just to be used by the callback. That would mean sending application state to the server which isn't a good thing as far as I'm concerned.

I like the idea of listening for certain events that the callback might emit during execution. The callback might emit a certain type of event each time it is run. The events are always emitted but the application may not always be listening. When the application is in a certain state, it will be listening. The handlers of these events could be considered secondary callbacks.