index.html

<html>
<head>
  <title>Simple Pubnub Hello World! Demo</title>
  <script src='http://cdn.pubnub.com/pubnub-3.5.1.min.js'></script>
  <script>
    (function(){

      // initializes pubnub keys
      var pubnub = PUBNUB.init({
        publish_key: 'demo',
        subscribe_key: 'demo'
      });

      // function that listens to the 'hello_world' channel while subscribed & alerts message pased in from publish function
      pubnub.subscribe({
        channel: 'hello_world',
        message: function(m) { alert(m) },
        connect: publish 
      });

      // function that sends a message via channel to user who is subscribed to that channel.
      function publish() {
        pubnub.publish({
          channel: 'hello_world',
          message: 'welcome to a simple pubnub example!'
        })
      }
    })()
  </script>
</head>
<body>

</body>
</html>