minimal event emitter for single value type

echo.ts

interface Listener<T> {
	(value: T): void;
}

class Echo<T> implements Disposable {
	private listeners = new Set<Listener<T>>();

	listen(listener: (value: T) => void) {
		this.listeners.add(listener);
		return new Disposable(() => {
			this.listeners.delete(listener);
		});
	}

	push(value: T) {
		this.listeners.forEach(listener => listener(value));
	}

	dispose() {
		this.listeners.clear();
	}
}