A topic-based subscribe-publish library written in JavaScript.

MessageBus.js

/*
 * Observer.js
 *
 * SYNTAX:
 *    const EventHandler = new MessageBus( context );
 * ---
 *    context: identifier for the event handler
 * ---
 * USAGE:
 *    var handler = new MessageBus( document );
 */
function MessageBus(id) {
  const context = typeof id === "undefined" ? document : id;
  const topics = {};
  const hOP = topics.hasOwnProperty;

  return {
    subscribe: function(topic, listener) {
      // Create the topic's object if not yet created
      if (!hOP.call(topics, topic)) {
        topics[topic] = [];
      }

      // Add the listener to queue
      let index = topics[topic].push(listener) - 1;

      // Provide handle back for removal of topic
      return {
        remove: function() {
          delete topics[topic][index];
        }
      };
    },
    publish: function(topic, info) {
      // If the topic doesn't exist, or there's no listeners in queue, just leave
      if (!hOP.call(topics, topic)) {
        return;
      }

      // Cycle through topics queue, fire!
      topics[topic].forEach(function(item) {
        item(info !== undefined ? info : {});
      });
    }
  };
}

export default MessageBus;