Question

Is there such a thing as listBox1_SelectedIndexChanged but in PHP ?

Answer 1

Nope, but you could use jQuery 🙂

$(document).ready(function() {
    $("#selectList").change(function() {
        var myVal = $(this).val();
        alert(myVal);
    });
});

If you need to send data to server and get back from it, use $.post() / $ajax() etc …