notifications without reloading the page (like facebook or google plus notifications)

Question

What would be the ideal mechanism to get notifications like in Facebook in to a dashboard ?. I am thinking the best way is to do a Ajax call to a php page every 5 seconds and retrieve the notifications.

Is there any better way to do a similar change?

It should work in all mobile browsers too.

I am doing it the following way,

use $.post in jquery for get data without page refreshing.

$.post("page.php",{"act":1},function(data){
    $("#id").html(data);
});
in page.php write your query

EDIT 1

I wrote a function like this after referring to some online notes and its working in realtime.

var TimeStamp = null;
      function waitForMsg() {
         $.ajax({
            type: "GET",
            url: "getData.php?timestamp=" + TimeStamp,
            async: true,
            cache: false,
            timeout: 50000, /* Timeout in ms */
//          data: "TimeStamp=" + TimeStamp,
            success: function( data ) {
               var json = eval('(' + data + ')');

               if ( json['msg'] != "" ) {
                  alert( json['msg'] );
               }
               TimeStamp = json['timestamp'];

               setTimeout(
                   'waitForMsg()', /* Request next message */
                   1000            /* ..after 1 seconds */
               );
            },
            error: function( XMLHttpRequest, textStatus, errorThrown ) {
               alert("error:" + textStatus + "(" + errorThrown + ")");
               setTimeout(
                   'waitForMsg()', /* Try again after.. */
                    "15000");       /* milliseconds (15seconds) */
               },
            });
         }
      ;

      // calling after dom is ready
      $(document).ready(function() {
          waitForMsg();
      });

PHP file is,

<?php
   $filename = dirname(__FILE__).'/data.txt';
   $lastmodif = isset( $_GET['timestamp'] ) ? $_GET['timestamp'] : 0;
   $currentmodif = filemtime( $filename );

   while ( $currentmodif <= $lastmodif ) {
      usleep( 10000 );
      clearstatcache();
      $currentmodif = filemtime($filename);
   }

   $response = array();
   $response['msg'] = file_get_contents( $filename );
   $response['timestamp'] = $currentmodif;
   echo json_encode($response);

EDIT 2

All work well but when there is no changed happend to data.txt file i get a error message like this in 50 seconds.

error:timeout(timeout)

how can this be prevented ?

REF : Javascript Variable Scope

I'd think ajax posts at regular intervals would be the best way to do it. But then it raises the question that if someday you get, let's say, a billion users out of which 300 million are logged in at any given point of time, that'd mean 300 million calls to the PHP page every 5 seconds!! I'm curious to know what other approaches are there. — DS., Oct 14 '13 at 04:46
@DS. yes thats true, but i am looking for other alternatives. — dev1234, Oct 14 '13 at 04:48
@mazraara if you want to do it right look into a websocket server, socket.io is a popular one. — Pablo, Oct 14 '13 at 04:50
@mazraara - check this out, it might help - http://stackoverflow.com/questions/16860106/real-time-notification-from-web-server-to-client-bowers — DS., Oct 14 '13 at 04:50

score 4 · Accepted Answer · answered Oct 14 '13 at 05:02

From what I know, there are basically two ways to do this: polling, and websockets. Polling is either making many requests at an interval, or having a very long request the browser and server know is long (also called long polling). Then there is websockets. I haven't been in PHP land in a while, but last I checked websockets weren't really supported there. It could have changed. In Node world socket.io is a great solution that uses websockets and long polling as a backup.

A quick search has found this for websockets and php: http://socketo.me/docs/

notifications without reloading the page (like facebook or google plus notifications)

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