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Compare two dates using javascript

The text boxes will accept dates in many forms
(European vs U.S. date formats can be selected in the code.)
and will convert them automatically.

Here is the code:

<SCRIPT LANGUAGE="JavaScript">
function twdckdate(objName) {
var twdfielddate = objName;
if (twdchkdate(objName) == false) {
twdfielddate.select();
alert("Invalid Date Entry. Please try again.");
twdfielddate.focus();
return false;
}
else {
return true;
}
}
function twdchkdate(objName) {
var strDatestyle = "US"; //US dates
//var strDatestyle = "EU"; //EU dates
var strDate;
var strDateArray;
var strDay;
var strMonth;
var strYear;
var intday;
var intMonth;
var intYear;
var bloopercaught = false;
var twdfielddate = objName;
var strSeparatorArray = new Array("-"," ","/",".");
var intElementNr;
var err = 0;
var strMonthArray = new Array(12);
strMonthArray[0] = "Jan";
strMonthArray[1] = "Feb";
strMonthArray[2] = "Mar";
strMonthArray[3] = "Apr";
strMonthArray[4] = "May";
strMonthArray[5] = "Jun";
strMonthArray[6] = "Jul";
strMonthArray[7] = "Aug";
strMonthArray[8] = "Sep";
strMonthArray[9] = "Oct";
strMonthArray[10] = "Nov";
strMonthArray[11] = "Dec";
strDate = twdfielddate.value;
if (strDate.length < 1) {
return true;
}
for (intElementNr = 0; intElementNr < strSeparatorArray.length; intElementNr++) {
if (strDate.indexOf(strSeparatorArray[intElementNr]) != -1) {
strDateArray = strDate.split(strSeparatorArray[intElementNr]);
if (strDateArray.length != 3) {
err = 1;
return false;
}
else {
strDay = strDateArray[0];
strMonth = strDateArray[1];
strYear = strDateArray[2];
}
bloopercaught = true;
}
}
if (bloopercaught == false) {
if (strDate.length>5) {
strDay = strDate.substr(0, 2);
strMonth = strDate.substr(2, 2);
strYear = strDate.substr(4);
}
}
if (strYear.length == 2) {
strYear = '20' + strYear;
}
if (strDatestyle == "US") {
strTemp = strDay;
strDay = strMonth;
strMonth = strTemp;
}
intday = parseInt(strDay, 10);
if (isNaN(intday)) {
err = 2;
return false;
}
intMonth = parseInt(strMonth, 10);
if (isNaN(intMonth)) {
for (i = 0;i<12;i++) {
if (strMonth.toUpperCase() == strMonthArray[i].toUpperCase()) {
intMonth = i+1;
strMonth = strMonthArray[i];
i = 12;
}
}
if (isNaN(intMonth)) {
err = 3;
return false;
}
}
intYear = parseInt(strYear, 10);
if (isNaN(intYear)) {
err = 4;
return false;
}
if (intMonth>12 || intMonth<1) {
err = 5;
return false;
}
if ((intMonth == 1 || intMonth == 3 || intMonth == 5 || intMonth == 7 || intMonth == 8 || intMonth == 10 || intMonth == 12) && (intday > 31 || intday < 1)) {
err = 6;
return false;
}
if ((intMonth == 4 || intMonth == 6 || intMonth == 9 || intMonth == 11) && (intday > 30 || intday < 1)) {
err = 7;
return false;
}
if (intMonth == 2) {
if (intday < 1) {
err = 8;
return false;
}
if (LeapYear(intYear) == true) {
if (intday > 29) {
err = 9;
return false;
}
}
else {
if (intday > 28) {
err = 10;
return false;
}
}
}
if (strDatestyle == "US") {
twdfielddate.value = strMonthArray[intMonth-1] + " " + intday+" " + strYear;
}
else {
twdfielddate.value = intday + " " + strMonthArray[intMonth-1] + " " + strYear;
}
return true;
}
function LeapYear(intYear) {
if (intYear % 100 == 0) {
if (intYear % 400 == 0) { return true; }
}
else {
if ((intYear % 4) == 0) { return true; }
}
return false;
}
function TWDCompareDate(from, to) {
if (Date.parse(from.value) <= Date.parse(to.value)) {
alert("These dates work for me...how about you?");
}
else {
if (from.value == "" || to.value == "") 
alert("Please enter both dates.");
else 
alert("End date must occur after the Start date.");
}
}
// End -->
</script>

<center>
<form>
<div align="left"><span class="style1">
<strong>Start Date:</strong> 
<input type=text name=from onBlur="twdckdate(this)" size=11 maxlength=11>
</span> <span class="style1"><br>
<br>
<strong>End Date:&nbsp; </strong> </span>
<input type=text name=to onBlur="twdckdate(this)" size=11 maxlength=11>
<br>
<br>