Simple publish/subscribe implementation.

pub-sub.js

var Eventbus = {
  topics: {},
  
  /**
   * Adds topic to `topics` object if it doesn't exist
   * and adds listener to same topic.
   *
   * @param {string} topic
   * @param {function} listener
   */
  subscribe: function(topic, listener) {
    if (!this.topics[topic]) {
      
      // Add topic
      this.topics[topic] = [];
    }

    //Add listener to topic
    this.topics[topic].push(listener);
  },
  
  /**
   * Iterates over list of associated listeners for a topic.
   * Data is passed to each listener when called.
   * 
   * @param {string} topic the topic's label
   * @param {string} data the listeners will do something with this on publish
   */
  publish: function(topic, data) {
    
    // do nothing if topic doesn't exist or there are no listeners for topic.
    if (!this.topics[topic] || this.topics[topic].length < 1) {
      return;
    }
    
    // For each listener in topic...
    this.topics[topic].forEach(function(listener) {
      // call listener.
      listener(data);
    })
  }
}

// Listener
function say(msg) {
  console.log(msg);
}
// Listener
function shout(msg) {
  console.log(msg.toUpperCase() + '!!!!');
}

// Subscribe listeners to 'message' topic.
Eventbus.subscribe('message', say);
Eventbus.subscribe('message', shout);

/**
 * The `topics` object looks like this after a couple of subscribes:
 *
 * { 'message': [say, shout] }
 *
 * Eventbus will iterate over the topic array calling each listener
 * and passing in the data.
 */
Eventbus.publish('message', 'hello world'); // 'hello world', 'HELLO WORLD!!!!'