JavaScript: Bannercode Generator funktioniert nicht?!

<script type="text/javascript">
<!--// hiding this script from old browser
function generator(form)
form.result.value = '<a href="' + form.URL.value + '"><img src="' + form.Bild.value + '" alt=""></a>';
//-->
</script>
<form action="#" method="post">
Adresse: <input type="text" size="30" value="" name="URL" />
Bild URL: <input type="text" size="30" value="" name="Bild" />
<input type="button" value="Bannercode erstellen" onclick="javascript:generator(this.form);" />
Der generierte Bannercode: <textarea cols="40" rows="4" name="result" readonly="readonly"></textarea>