fetching php SESSION data in JSON fromat into html via jQuery and ajax

I'm facing a head messing situation while retrieving PHP SESSION details via ajax and jQuery.

Let me explain the whole situation.

My fetch.php [get and send the SESSION details]:

 header('Content-Type: application/json');
 session_name('admin');
 session_set_cookie_params(2*7*24*60*60);
 session_start();
 echo json_encode(array(
   'session'=>$_SESSION,
   'session'=>array(
     'user'=>$_SESSION['user'],
     'email'=>$_SESSION['email'],
     'rememberMe'=>$_SESSION['rememberMe']
   ),
 ));
 exit(0);

jQuery code to fetch the details :

 $.ajax({
   url: "fetch.php",
   type: "get",
   dataType: 'json',
   cache: false,
   success: function(data){
     user = data.session.user;
     email = data.session.email;
     rememberMe = data.session.rememberMe;
   }
 });

After fetching, I'm trying to add/remove something to my html [based on the session details]:

 if(user != null && user != undefined && user != "undefined"){
   //if 'user' is not 'null/undefined', it means that he is logged in, so add something
 }else{
   //remove the added item
 }

MAIN PHP :

 header('Content-Type: application/json');
 session_name('admin');
 session_set_cookie_params(2*7*24*60*60);
 session_start();

 if($_SESSION['user'] && !isset($_COOKIE['remember']) && !$_SESSION['rememberMe']){
   $_SESSION = array();
   session_destroy();
 }  

 //......

 if($_REQUEST['Login']){
   // ....
   $_SESSION['user']=$name;
   $_SESSION['email']=$email;
   if(isset($_POST['rememberMe'])){
     $_SESSION['rememberMe'] = $_POST['rememberMe'];
     setcookie('remember',$_POST['rememberMe']);
   }else{
     setcookie('oneTime','1');
   }
   // ....
 }

 //.......

 if($_REQUEST['Logout']){
   $_SESSION = array();
   session_destroy();
   $admin['msg'] = "Logout successful";
 }

Now, the main problem is, this code behave mysteriously/unpredictable... for testing purpose, I add

  alert(user);

just after my ajax code.

So, When I load the page, it alerts undefined, its good. But when I logged-in successfully {for example, logging-in with "try" user} it alerts null rather than the user name, and add the dynamic element to the html. It means, totally ignoring the if condition.

And when I refresh the page without logging-out, it alerts undefined and didn't remove the dynamically added element.

While I logout the user, it alerts the real user name {"try"} and remove the dynamically added elements [again, ignoring the if condition].

here is my jQ "login" code:

 $.ajax({
   url: $frm.attr('action')+'?'+name+'=true',
   type: $frm.attr('method'),
   data: serial,
   success: function(response){
     //.....
   }
 });

can somebody tell me that where i'm doing wrong....

And sorry for typo OR grammatical mistakes.

UPDATE:

some code from my main.js:

 var handler = {
   init: function(){
     $.ajax({
       url: "fetch.php",
       type: "get",
       dataType: 'json',
       cache: false,
       success: function(data){
         user = data.session.user;
         email = data.session.email;
         rememberMe = data.session.rememberMe;
       }
     });
     alert(user);  // echoing the value of user
     if(user != null && user != undefined && user != "undefined"){
       //....... dynamically add the element is user is logged-in
     }else{
       //...... remove the dynamically added element
     }
     handler.submit();
   },
   submit: function(){
    $('html').on('click','.submit',function(e){
       var $frm = $(this).parents('form');
       var serial = $frm.serialize();
       var name = $(this).attr('name');
       $.ajax({
         url: $frm.attr('action')+'?'+name+'=true',
         type: $frm.attr('method'),
         data: serial,
         success: function(response){
             //....... on success : some code
         }
       });
       setTimeout(function(){handler.init();},5000);
       e.preventDefault();
     });
   }
 };
 $(document).ready(handler.init);