typed-emttier.ts

type Listener<T extends Array<any>> = (...args: T) => undefined

type EventMap = {
	[index: string]: any[]
}

class TypedEvents<Events extends EventMap> {
	private events: {
		[K in keyof Events]?: Listener<Events[K]>[]
	} = {}
	
	addEventListener<K extends keyof Events>(event: K, listener: Listener<Events[K]>){
		this.events[event] = this.events[event]	|| [];
		this.events[event].push(listener);
	}

	removeEventListener<K extends keyof Events>(event: K, listener: Listener<Events[K]>){
		this.events = this.events || {};
		if (event in this.events) {
			const index = this.events[event].indexOf(listener);
			if (index !== -1) {
				this.events[event].splice(index, 1);
			}
		}
	}

	dispatch<K extends keyof Events>(event: K, ...data: Events[K]){
		if (event in this.events) {
			for (const listener of this.events[event]) {
				listener(...data);
			}
		}
	}

	on = this.addEventListener;
	off = this.removeEventListener;
	emit = this.dispatch;
};

type MyEvents = {
	boogersExcavated: [number],
	consumptionComplete: [string]
}

const thing = new TypedEvents<MyEvents>()

thing.on('boogersExcavated', (num) => console.log(num));

thing.emit('boogersExcavated', 1);