function createEventEmitter<T>() {
    let listeners: ((action: T) => void)[] = [];
    return {
        subscribe,
        dispatch,
    };

    function subscribe(listener: (action: T) => void) {
        listeners.push(listener);
        return function unsubscribe() {
            const idx = listeners.findIndex(f => f === listener);
            listeners.splice(idx, 1);
        };
    }

    function dispatch(action: T) {
        listeners.forEach(f => f(action));
        return action;
    }
}


/* Demo */

interface Foo {
    type: 'FooAction';
    payload: number;

}
interface Bar {
    type: 'BarAciton';
    payload: string;
}

type ActionTypes = Foo | Bar;


const ee = createEventEmitter<ActionTypes>();


ee.subscribe((action) => {
    switch (action.type) {
        case 'FooAction':
            return action.payload;
        default:
            break;
    }

});

ee.dispatch({ type: 'FooAction', payload: 1 });