Paginetta d'esempio:
codice:
<script>
function isDate(str) { 
	spz = str.split("/"); 
	dat = new Date(spz[2], spz[1]-1, spz[0]); 
	if	( 
		dat.getFullYear() == parseFloat(spz[2]) &&
		dat.getMonth() == (parseFloat(spz[1])-1) &&
		dat.getDate() == parseFloat(spz[0]) 
		) {
			return dat;
	}
	return false;
} 

function testD(obj) {
	obj.style.background='white'
	RE = /[^\d^/^\-^\.]/gi
	obj.value=obj.value.replace(RE,"");
	RE = /[\-\.]/gi
	obj.value=obj.value.replace(RE,"/");

	if (!isDate(obj.value)&&obj.value!="") {
		alert("Data Errata")
		obj.style.background='yellow'
		obj.focus()
	} 
}
function calcola(f) {
d1 = isDate(f.data1.value)
d2 = isDate(f.data2.value)
d3 = 0
if (d1&&d2) {
	d3 = Math.abs(d2-d1)
	alert(Math.floor(d3/(24*60*60*1000)))
}
}
</script>
</HEAD>

<BODY>
<form>
<input type=text size=12 name=data1 onblur="testD(this)">
<input type=text size=12 name=data2 onblur="testD(this)">
<input type=button value=Calcola onclick="calcola(this.form)">
</BODY>
ciao