HTML表单适用于桌面但不适用于移动设备

Question

I have an HTML form to send a small 20 character message to a MySQL table. It works wonderfully on my desktop while running Firefox 49 but on my friend's IPhone with IOS 9.3.3 and using the Safari browser it dose not work at all. I've spent a few hours googling to try and find the cause of the issue. Anyway here is my code:

Form things:

<iframe id="target-frame" name="target-frame"></iframe>
<form id="mark-form" target="target-frame" action="make_mark.php" method="post">
    You have 20 characters, use them wisely. <br>
    <input type="submit" value="Mark" onclick="timeoutMark()"></input>
    <input type="text" name="mark" maxlength="20"></input>
</form>

<script>
var timeoutMark = function timeoutMark() {
    setTimeout(markForm, 5);
}
var markForm = function markForm() {
    document.getElementById('mark-form').reset();
    location.reload();
}
</script>

make_mark.php:

include($_SERVER['DOCUMENT_ROOT']."/paths.php");
include($path['mysql']);
$mark = db_quote($_POST['mark']);
$ip = db_quote($_SERVER['REMOTE_ADDR']);
echo "<textarea>".$mark."</textarea>";

if ($mark == "''") {
    exit("Mark is empty");
}
$query = db_query("INSERT INTO marks (mark, ip) VALUES (" . $mark . "," . $ip . ")");