php script code executing on page reload within a javascript function

Question

I am initialising the session with the variable name fromSelectStudentPage to 1 when the button CONTINUE is clicked.

when i reload the page just for testing the session gets initialised to 1 even without calling the function.

<form id="forStudent">
     <button type="button" on-click="onSelectStudent();">CONTINUE</button>
</form>

function onSelectStudent() {
    if(checkStudType()) {
        <?php $_SESSION['fromSelectStudentPage'] = '1'; ?>
        $('form#forStudent').submit();  
    }
}