https://catarine-nickel.de/modules/newsletter/formfunctions.js?v=5.6.3

1
2//datepicker
3function checkdate(docform){
4	var fdate = "";
5	for(var i=0;i<docform.elements.length;i++){
6		if(docform.elements[i].name.substring(0,9) == "dtDateDay"){
7			var d = docform.elements[i].value;
8			var m = docform.elements[i+1].value;
9			var y = parseInt(docform.elements[i+2].value);
10			if(y < 2000) y = y<80?y+2000:y+1900;
11			var febdays = y%400==0?29:y%100==0?28:y%4==0?29:28;
12			var monthdays = new Array(31,febdays,31,30,31,30,31,31,30,31,30,31);
13			if(d=="00" || m=="00" || y=="" || monthdays[m-1]<d){
14				alert("Invalid date");
15				docform.elements[i].focus();
16				return(false);
17			};
18			continue;
19		};
20	};
21	return(true);
22};
23
24function checklength(num){
25	num = num.toString()+"";
26	if(num.length == 1) num = "0" + num;return(num);
27};