EventListener and the quest of the minimal pubsub

EventEmitter.js

class EventEmitter extends Map {        
    on (e,f){ this.set(e, [...this.get(e)||[], f]) }
    off(e,f){ this.set(e, (this.get(e)||[]).filter(x => f && x !== f)) }
    emit(e,...a){ (this.get(e)||[]).map(f => f(...a)) }
}

// minified classless fit-in-a-tweet version
E=(M=new Map,_=e=>M.get(e)||[])=>({on(e,f){M.set(e,[..._(e),f])},off(e,f){M.set(e,_(e).filter(x=>f&&f!==x))},emit(e,a){_(e).map(f=>f(a))}})

// Usage example:

var observable = E(); // or new EventEmitter()
function log(n){ console.log(n); }
observable.on("myEvent", log)
observable.emit("myEvent", 1)
observable.on("anotherEvent", x => log(2*x))
observable.emit("anotherEvent", 1)
observable.on("myEvent", function(){ console.log(3) })
observable.off("myEvent", log);
observable.emit("myEvent")
observable.off("myEvent");
observable.on("anotherEvent", function(){ console.log(5) })
observable.emit("anotherEvent", 2);
// 1 2 3 4 5