ES6 Simple global PubSub system

pub_sub.js

export class PubSub {
    constructor (){
        this.subscriptions = {};
    }

    subscribe (event, subscriber) {
        if (typeof this.subscriptions[event] === 'undefined') {
            this.subscriptions[event] = new Set();
        }
        this.subscriptions[event].add(subscriber);
    }

    fire (event, payload) {
        let subscribers = this.subscriptions[event];
        if (subscribers) {
            subscribers.forEach((subscriber) => {
                subscriber(payload, event);
            });
        }
    }
}

if (typeof window.PubSub === 'undefined') {
    window.PubSub = new PubSub();
}