javascript - Display an alert box in php and navigate back -

i want display javascript alert box in php , navigate main page. here code

    session_start();     $name= $_session['name'];              $id= $_session['id'];             //check if guest              if($name=="guest"){         echo'<script type="text/javascript">alert(" not allowed view contnent"); </script>';         header('location: mainpage.php');     }     //the rest of page 

with code alert popup not displayed redirection. try this

$name= $_session['name'];     $id= $_session['id'];     //check if guest      if($name=="guest"){          echo'<script type="text/javascript">window.alert(" not allowed view contnent");</script>';         echo'<script type="text/javascript> window.navigate("mainpage.php"); </script>';      }             //the rest of page 

now popup displayed redirection not work.

$name= $_session['name'];     $id= $_session['id'];     //check if guest      if($name=="guest"){          echo'<script type="text/javascript">window.alert(" not allowed view contnent");</script>';         echo'<script type="text/javascript> window.location.href="mainpage.php"; </script>';      } 

please review code