Button submit без перезагрузки

<?php 
$answ1 = filter_input(INPUT_POST, 'radio');
$answ2 = filter_input(INPUT_POST, 'radio2');
if ($answ1 !== null && $answ2 !== null) {
    $right = 0;
    $wrong = 0;
    $answ1 == 1 ? $right ++ : $wrong ++;
    $answ2 == 3 ? $right ++ : $wrong ++;
    exit(json_encode(['right' => $right, 'wrong' => $wrong]));
}
?>
<div id="iq"></div>
<form action="test.php" method="post" id="govnokod">
    <h5> <b>1.</b> Jak ... na imię?</h5>
    <input type="radio" name="radio" value="1"> masz <br>
    <input type="radio" name="radio" value="2"> mam <br>
    <input type="radio" name="radio" value="3"> mieć <br>
    <h5> <b>2.</b> ... matka bardzo dobrze gotuje.</h5>
    <input type="radio" name="radio2" value="1"> mój <br>
    <input type="radio" name="radio2" value="2"> ją <br>
    <input type="radio" name="radio2" value="3"> moja <br>
    <input type="submit" id="submit">
</form>
<script>
    document.querySelector('#govnokod').addEventListener('submit', function(evt) {
        evt.preventDefault();
        function Success(e) {
            if (req.readyState == 4) {
                if (req.status == 200) {
                    var res = JSON.parse(e.currentTarget.response);
                    document.querySelector('#iq').innerText = 'Правильно: ' + res.right + ' неправильно ' + res.wrong;
                }
            }
        }
        var answ1 = document.querySelector('input[name=radio]:checked') === null ? 0 : document.querySelector('input[name=radio]:checked').value;
        var answ2 = document.querySelector('input[name=radio2]:checked') === null ? 0 : document.querySelector('input[name=radio2]:checked').value;
        var params = "radio=" + answ1 + "&radio2=" + answ2;
        var req = new XMLHttpRequest();
        req.open('POST', 'test.php', true);
        req.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
        req.onreadystatechange = Success;
        req.send(params);
    })
</script>