Destroy session upon refresh

$value = $_SESSION["data"];
    $query = "SELECT * FROM datas WHERE CONCAT(`code`,`name`, `ID`, `cost`) LIKE '%".$value."%'";
    $search = filterTable($query);
if (isset($_SESSION["data"])) {
   if (basename($_SERVER['PHP_SELF']) != $_SESSION["data"]) {
        session_unset();
   }
}

unset($_SESSION['data']);

$_SESSION = array();

session_destroy();
$_SESSION = array();

//put this line of code in that page you are planning to refresh.
window.onbeforeunload = function() {
      if (typeof XMLHttpRequest != "undefined"){
                xmlHttp= new XMLHttpRequest();
                }
                else if (window.ActiveXObject){
                    xmlHttp= new ActiveXObject("Microsoft.XMLHTTP");
                }
                if (xmlHttp==null){
                    alert("Browser does not support XMLHTTP Request")
                    return;
                }
                var base_url="<?php echo base_url(); ?>"
                var url=base_url + 'controller/function_name';
               // url +=id;
                xmlHttp.onreadystatechange = stateChange;
                xmlHttp.open("GET", url, true);
                xmlHttp.send(null);

  };

//your function in php will be 

public function function_name(){

        $newdata =  array(

                            'session_variable' =>0       
                    );

        $this->session->set_userdata($newdata);
    }