update javascript variable inside AJAX call

Question

I want to get section_id from php session by ajax call

it return undefined

<?php   $_SESSION['active_sectionid']=  intval($_GET["section_id"]); ?>

<script>
function get_sectionid() {
    $.ajaxSetup({cache: false});
        $.get('/ajax/getsession.php', function (data) {
        return data;
    });
    return ;
}

$(document).ready(function (e) {
    var section_id;
    $('.section_selected').on('click', function (e) {   
        section_id=get_sectionid();
        alert(section_id);
   });
});
</script>

getsession.php

<?php
if (session_status() == PHP_SESSION_NONE) session_start();
echo  $_SESSION['active_sectionid'];
?>

or any idea to update section_id after jaxa call