Implement websockets with javascript and socket.io

- What is Socket.IO?

  -- Socket.IO is an event-based bi-directional communication layer for realtime web applications, built atop Engine.IO that allows developers to send and receive data without worrying about cross-browser compatibility.
  -- It abstracts many transports, including AJAX long-polling and WebSockets
  -- It has two parts: a client-side library that runs in the browser, and a server-side library for node.js. Both components have a nearly identical API.
  
- SERVER SIDE:

  -- Server()
  Creates a new Server (works with and without new):

  var socket_server = require('socket.io')();

  // or

  var Server = require('socket.io');
  var socket_server = new Server();

  //Choose port that server should listen to
  var socket_port = 3001;

  socket_server.on("connection", function(socket_event) {
    var tweet = {user: "nodesource", text: "Hello, world!"};

    // to make things interesting, have it send every second
    var interval = setInterval(function () {
      socket_event.emit("tweet", tweet);
    }, 1000);

    socket_event.on("disconnect", function () {
      clearInterval(interval);
    });	
  });

  // or


  var handleClient = function (socket_event) {  
    var tweet = {user: "nodesource", text: "Hello, world!"};

    // to make things interesting, have it send every second
    var interval = setInterval(function () {
      socket_event.emit("tweet", tweet);
    }, 1000);

    socket_event.on("disconnect", function () {
      clearInterval(interval);
    });
  };

  socket_server.on("connection", handleClient);

  server.listen(socket_port);

- CLIENT SIDE:

<script src="/socket.io/socket.io.js"></script>  
<script>

  //Choose a port for message exchange between client and server
  var socket_port = 3001; //must be the same port configured on server-side
  
	var socket_event = io.connect("http://localhost:" + socket_port);
  
  //or
   
  var socket_event = io.connect("http://" + window.location.hostname + ":" + socket_port);

	socket_event.on("tweet", function(tweet) {
  
	    // todo: add the tweet as a DOM node
	    console.log("tweet from", tweet.user);
	    console.log("contents:", tweet.text);
	});
</script>


- EMIT

-- socket_event.emit(<event_name>, <data_to_emit>): Send message only to the 'client' (either browser or webserver) who triggered the event
-- socket_event.broadcast.emit(<event_name>, <data_to_emit>): Send message to every connected 'client' (only available on webserver), except to the one who triggered the event
-- io.sockets.emit(<event_name>, <data_to_emit>): Send message to every connected 'client' (either browser or webserver). The 'client' who triggered the event will also receibe this message.


REFERENCES:
  -- https://www.tutorialspoint.com/socket.io/socket.io_quick_guide.htm
  -- http://www.programwitherik.com/socket-io-tutorial-with-node-js-and-express/
  -- https://howtonode.org/websockets-socketio