checkbox item value on function click and php

i have a div with 2 checkbox items ( Employee / Teacher ) and a button with on click function that alerts the value of the chosen check items through javascript, and then i wanna assign these values to a variable that i want to use in php, the result is always Teacher ( even thought in the alert i get the correct value ex: Employee ), what am i doing wrong? my code is the following :

<div class="form-group">

    <label style="text-align: left;" class="control-label col-sm-3">Type</label>

    <div class="col-sm-3">
    Employee<input type="checkbox" name='checkbox0' value="Employee" >
    Teacher<input type="checkbox" name='checkbox1' value="Teacher" >
            <input type="button" id="envoyer" value="Envoyer Reponse"/>
    </div>                   

    <script>

        $("#envoyer").click(function(e) {
        var myArray = [];
        $(":checkbox:checked").each(function() {
            myArray.push(this.value);
        });

        alert(myArray.join(","));

        var a=myArray.join(",");

       if (a=='Employee') { <?php $a='Employee'; ?> } else if (a=='Teacher') {      <?php $a='Teacher'; ?>         }
});

    </script>

</div> <!-- /.form-group -->

<?php echo $a; ?>