Can we take a moment to recognize how absolutely retarded JS' event system is?
Events aren't objects. No, they're managed by an object, and identified by a string.
To subscribe to an event, you call object.addEventListener(name, callback). Because for some reason we can't just have an event object. Events MUST have an owner.
But to unsubscribe you don't call the function addEventListener returned, you don't use the token it returned either. No, you pass the same function to removeEventListener.
Because we don't use serializable tokens like in PP, and we don't return functions like in FP, no, we use functions as tokens, realising idiomatic DFP.