Cijfers Input alleen

<form action='<? echo $_SERVER['PHP_SELF']; ?>' method="post">
<br />Gok:
<br /><input type="text" name="gok">
<br /><input type="submit" name="submit" value="Gok !">
</form>

<form action='<? echo $_SERVER['PHP_SELF']; ?>' method="post">
<br />Gok:
<br /><input type="text" name="gok">
<br /><input type="submit" name="submit" value="Gok !">
</form>

<script type="text/javascript">
window.onload = function() {
    var numberObject = document.getElementById('number');
    numberObject.onkeyup = function() {
        numberObject.value = numberObject.value.replace(/[^0-9]/, '');
    }
}
</script>
<input type="text" id="number" />

<script type="text/javascript">
window.onload = function() {
    var numberObject = document.getElementById('number');
    numberObject.onkeyup = function() {
        numberObject.value = numberObject.value.replace(/[^0-9]/, '');
    }
}
</script>
<input type="text" id="number" />