codice:
<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Pagina vuota</title>
<script type="text/javascript">
function increaseDay(nDelta) {
	var aFragms = document.myForm.myDate.value.split("."), oNewDate = new Date(parseFloat(aFragms[2]), parseFloat(aFragms[1]) - 1, parseFloat(aFragms[0]) + nDelta);
	document.myForm.myDate.value = oNewDate.getDate() + "." + String(oNewDate.getMonth() + 1) + "." + oNewDate.getFullYear();
	document.myForm.submit();
}
</script>
</head>

<body>
<iframe name="myIframe" src="http://www.google.it" style="width:100%;height:200px;margin-bottom:100px;"></iframe>
<form name="myForm" target="myIframe" method="post">
<fieldset>
<legend>Data</legend>
<input type="text" name="myDate" value="13.2.1999" />
<input type="button" value="+" onclick="increaseDay(1);" />
<input type="button" value="-" onclick="increaseDay(-1);" />
</fieldset>
</form>
</body>
</html>