JavaScript NON È Java!

codice:
<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Documento HTML</title>
<script type="text/javascript">

function getExpiration () {

	var

		aDateParts = document.getElementById("data_inserimento").value.replace(/\-(\d{1,2})$/, "-20$1").split("-"),
		oExpDate = new Date((new Date(parseFloat(aDateParts[2]), parseFloat(aDateParts[1]) - 1, parseFloat(aDateParts[0]))).getTime() + parseFloat(this.value) * 864e5);

	document.getElementById("data_scadenza").value = oExpDate.getDate() + "-" + (oExpDate.getMonth() + 1) + "-" + oExpDate.getFullYear().toString().replace(/(^\d{2})/, "");

}

onload = function () {
	var oDaysCount = document.getElementById("conteggio_giorni");
	oDaysCount.onpaste = oDaysCount.oncut = oDaysCount.onkeyup = oDaysCount.onblur = getExpiration;
};

</script>

</head>
 
<body>

<form name="tuoForm">
<input type="text" id="data_inserimento" value="01-12-13" />
<input type="text" id="conteggio_giorni" />
<input type="text" id="data_scadenza" />
</form>

</body>
</html>