evt.evt[Attach|Detach]

evt.evtAttach and evt.evtDetach are accessors for Evt<Handler<T, any>> that posts every time a new handler is attached to/detached from the Evt<T>.

import { Evt } from "evt";
const evtText= new Evt<string>();
function myCallback(text: string){};
evtText.getEvtAttach().attach(
handler=> console.log(`${handler.callback.name} attached`)
);
evtText.getEvtDetach().attach(
handler=> console.log(`${handler.callback.name} detached`)
);
//"myCallback attached" is printed to the console.
evtText.attach(callback);
//"myCallback detached" is printed to the console.
evtText.detach();

Run the example