Publish/Subscriber pattern

pubsub.js

const pubsub = (function(){
  
  let topics = {};
  let subUid = -1;
  let oneId = '';

  function publish(topic, args) {
    if(!topics[topic]) return false;
    let subscribers = topics[topic],
      len = subscribers ? subscribers.length : 0;
    while(len--) subscribers[len].func(topic, args);
    return this;
  }

  function once(topic, func) {
    oneId = subscribe(topic, function() {
      func.apply(this, arguments); 
      unsubscribe(oneId);
    }); 
    return this;
  }

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

  function unsubscribe(token) {
    for(let topic in topics) {
      if(!topic) return this;
      topics[topic].splice(
        topics[topic].indexOf(token),1
      );
      return token;
    } 
  }

  return {
    on: subscribe, 
    off: unsubscribe,
    one: once,
    fire: publish
  }

}());