topic based simple async pub-sub implementation

example_usage.js

//Example Usage

var seeker1 = function(msg) {
  console.log("seeker1 called: " + msg);
}

var seeker2 = function(msg) {
  console.log("seeker2 called: " + msg);
}

var Sub_Seeker1 = SK_PubSub.subscribe("JOB", seeker1);
//or 
SK_PubSub.subscribe("JOB", seeker2);

//Publish New Job
SK_PubSub.publish("JOB", "New Job Posted: Post 1");

SK_PubSub.unsubscribe("JOB", seeker2);
SK_PubSub.publish("JOB", "New Job Posted: Post 2");

//Unsubscribe seeker1
Sub_Seeker1.remove();

//Unsubcribe all seekers from "JOB" topic
SK_PubSub.unsubscribeAll("JOB");

//keep pubblishing new job
SK_PubSub.publish("JOB", "New Job Posted: Post 3");

//whoever comes first, get all queued message
SK_PubSub.subscribe("JOB", seeker2);

//Create new channel and subscribe receiver
var subscriber = SK_PubSub.subscribe("GAME", seeker1); 

SK_PubSub.publish("GAME", "cricket match ");
SK_PubSub.publish("JOB", "New Job Posted: Post 4");

sk_pub_sub.js

// Code goes here
/*
  About:
    Simple Async Pub-Sub implementation

  Usage:
    
    Create Subscriber
      seeker = function(msg){
        //---task to do on new 'msg' arrival
      }
      
    //Subscribe to a topic
    var sub_seeker =   SK_PubSub.subscribe("JOB", seeker);
    
    Publish message
      SK_PubSub.publish("JOB", {a:1, b:2, c:3 } )
    
    Unsubscribe
      SK_PubSub.unsubscribe("JOB", seeker);
      or
      sub_seeker.remove()
      
    Unsubscribe all subscribers
      SK_PubSub.unsubcribeAll("JOB");

*/


SK_PubSub = (
  function() {
    var topics = [];
    var subscribers = [];
    var messages = [];
    var self = this;
    return {

      subscribe: function(topic, subscriber) {
        //subscriber should be function
        if (typeof subscriber !== "function") {
          throw "subscriber should be a function";
        }
        // create topic if doesn't exist
        if (topics.indexOf(topic) < 0) {
          topics.push(topic);
          subscribers[topic] = [];
          messages[topic] = [];
        }

        //warn if susbcriber already added
        if (subscribers[topic].indexOf(subscriber) >= 0) {
          console.log("WARNING: Subscriber already added");
          return true;
        }

        //add subscriber
        subscribers[topic].push(subscriber);
        console.log("New subscriber added " + subscribers[topic].length);

        //give all pending messages
        messages[topic].forEach(function(msg) {
          setTimeout(function() {
            subscriber.call(this, msg);
          }, 0);
        });
        
        return {
          remove : function(){
            subscribers[topic].splice(subscribers.indexOf(subscriber), 1);
            console.log("Unsubscribed");
          }
        }

        return true;
      },

      publish: function(topic, pubObj) {
        //let pubObj be anything: string or object 
        if (typeof pubObj === "function") {
          throw "Not a valid publish data. Use string or object ";
        }

        //add message
        messages[topic].push(pubObj);

        //return if no subscriber
        if (subscribers[topic].length === 0) {
          console.log("no subcribers yet");
          return 0;
        }

        //call all subscribers
        var subs = subscribers[topic];
        subs.forEach(function(subscriber) {
          messages[topic].forEach(function(msg) {
            setTimeout(function() {
              subscriber.call(this, msg);
            }, 0);
          });
        });

        //clear message
        messages[topic] = [];

      },

      unsubscribe: function(topic, subscriber) {
        if (typeof subscriber != "function") {
          throw "not a valid subscriber";
        }
        subscribers[topic].splice(subscribers.indexOf(subscriber), 1);
        console.log("Unsubscribed");
      },

      unsubscribeAll: function(topic) {
        if (topics.indexOf(topic) < 0) {
          console.log("Warn: Invalid topic. No such topic")
          return 0;
        }
        //total subscribers
        var t_sub = subscribers[topic].length;
        //just empty the topic
        subscribers[topic] = [];
        return t_sub;
      },

    }

  }()
);