How to send messages from server to client?

Question

I am going to implement something similar to Facebook notification and this website (StackOverflow\'s notification which is notifying us if anyone write a comment/answer etc for

Answer 1

Check for update from server on every 30 Seconds or as per requirement.

window.setInterval(function(){
  /// call your function here
 //Make AJAX call
 //Update Respective HTML Contact i,e, DIV

}, 30000);