Ajax, Update div with num_rows - php

Question

I've built a notification system, and its almost working. I just have one niggly bit that I can't seem to get my head around.
When a new update comes in from a friend it prints out the number of new notifications as expected, only if a user posts twice num_rows 2 pops up.. but if a user posts again it updates and replaces the 2 new notifications number back to 1 in the div because I'm using html in the ajax to replace.
So my question is, how can I update the div to get the total amount of results so it goes 1,2,3,4 etc instead of 2,1,1,1,1.
I don't want to replace the num of new rows with only the (1) update in the div, just add to the amount of new updates already inside it.
A bit like when facebook shows amount of notifications. say I have two and a friends posts on my wall I then will have 3.. but at the moment its adding the last new num row and going back to 1.
AJAX
<script type="text/javascript">
function loadIt() {
var notification_id="<?php echo $notification_id['notification_id'] ;?>"
var notification_id= window.localStorage.getItem ('lastId');
$.ajax({
type: "GET",
url: "viewajax.php?notification_id="+notification_id,
dataType:"json",
cache: false,
success: function(response){
if(response){
dataHandler;
if(response.num){
window.localStorage.setItem('lastId', response.notification_id);
var dataHandler = function(response){
var isDuplicate = false, storedData = window.localStorage.getItem ('lastId');
for (var i = 0; i < storedData.length; i++) {
if(storedData[i].indexOf(response) > -1){
isDuplicate = true;
}
}
if(!isDuplicate){
storedData.push(response);
}
};
if(response){
if(response.num){
$("#notif_actual_text-"+notification_id).prepend('<div id="notif_actual_text-'+response['notification_id']+'" class="notif_actual_text">'+response['notification_content']+' <br />'+response['notification_time']+'</div></nr>');
$("#mes").html(''+ response.num + '');
}
};
}
}
}
});
}
setInterval(loadIt, 10000);
PHP
$json = array();
$com=mysqli_query($mysqli,"select notification_id,notification_content,notification_time from notifications where notification_id > '$id' AND notification_status=1 ");
echo mysqli_error($mysqli);
$num = mysqli_num_rows($com);
if($num!=1){
$json['num'] = $num;
}else{
$json['num'] = 0;
}
$resultArr = mysqli_fetch_array($com);
$json['notification_id'] = $resultArr['notification_id'];
$json['notification_content'] = $resultArr['notification_content'];
mysqli_free_result($com);
header('Content-Type: application/json');
echo json_encode($json);
}

Answer 1

The number of notifications on client-side is storedData.length.
So i would replace the counter
$("#mes").html(''+ response.num + '');
with
$("#mes").html(storedData.length);