Simple PubSub implementation with JavaScript - taken from Addy Osmani's design patterns book -

pubsub-simple.js

var pubsub = {};
(function(q) {
    var topics = {}, subUid = -1;
    q.subscribe = function(topic, func) {
        if (!topics[topic]) {
            topics[topic] = [];
        }
        var token = (++subUid).toString();
        topics[topic].push({
            token: token,
            func: func
        });
        return token;
    };

    q.publish = function(topic, args) {
        if (!topics[topic]) {
            return false;
        }
        setTimeout(function() {
            var subscribers = topics[topic],
                len = subscribers ? subscribers.length : 0;

            while (len--) {
                subscribers[len].func(topic, args);
            }
        }, 0);
        return true;

    };

    q.unsubscribe = function(token) {
        for (var m in topics) {
            if (topics[m]) {
                for (var i = 0, j = topics[m].length; i < j; i++) {
                    if (topics[m][i].token === token) {
                        topics[m].splice(i, 1);
                        return token;
                    }
                }
            }
        }
        return false;
    };
}(pubsub));

While above is good, and it's crazily 7 years old. I try below method. Instead of using an array, I use an object for each subscriptions as well. Simpler and smaller Also note the unsubscribe closure return in publish, kinda helps.

PubSub.js

class PubSub {
  constructor () {
    this.subIds = 0;
    this.subscriptions = {}
  }
  
  subscribe (topic, fn) {
    if(!this.subscriptions[topic]) this.subscriptions[topic] = {}
    const token = ++this.subIds;
    // Validate topic name and function constructor
    this.subscriptions[topic][token] = fn;
    
    return () => this.unsubscribe(topic, token)
  }
  
  publish (topic, ...args) {
    const subs = this.subscriptions[topic];
    if(!subs) return false
    Object.values(subs).forEach(sub => sub(...args))
  }
  
  unsubscribe (topic, token) {
    if(!token) delete this.subscriptions[topic]; // Delete all subscriptions for the topic
    this.subscriptions[topic] && (delete this.subscriptions[topic][token]); // Delete specific subscription
  }
}

export default new PubSub();

Example

const unsub1 = PubSub.subscribe('spacex', data => console.log('Falcon was launched', data));
const unsub2 = PubSub.subscribe('spacex', data => console.log('Falcon Heavy was launched', data));
PubSub.publish('spacex', 'some data slash params')

// Unsubscribe single subscription
unsub1(); // Unsubscribes Falcon
unsub2(); // Unsubscribes Falcon Heavy

// Unsubscribe ALL subscriptions for a topic
PubSub.unsubscribe('spacex')

This isn't publish subscribe pattern, this is the simplest observer pattern.

How can I use this as a subscriber

@scazzy thank you it's precisely what i needed