Check for Valid Date using JavaScript

Ivin Raj S
Nov 18, 2013
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Check for valid date using JavaScript. below is the full code.

<head id="Head1" runat="server">
  <title>Untitled Page</title>
   <script language="javascript" type="text/javascript">
// Declaring valid date character, minimum year and maximum year
  var dtCh = "/";
  var minYear = 1900;
  var maxYear = 2100;
  function isInteger(s) {
  var i;
  for (i = 0; i < s.length; i++) {
   // Check that current character is number.
  var c = s.charAt(i);
  if (((c < "0") || (c > "9"))) return false;
}
   // All characters are numbers.
  return true;
}
  function stripCharsInBag(s, bag) {
  var i;
  var returnString = "";
   // Search through string's characters one by one.

   // If character is not in bag, append to returnString.
  for (i = 0; i < s.length; i++) {
  var c = s.charAt(i);
  if (bag.indexOf(c) == -1) returnString += c;
}
  return returnString;
}
  function daysInFebruary(year) {
   // February has 29 days in any year evenly divisible by four,
   // EXCEPT for centurial years which are not also divisible by 400.
  return (((year % 4 == 0) && ((!(year % 100 == 0)) || (year % 400 == 0))) ? 29 : 28);
}
  function DaysArray(n) {
  for (var i = 1; i <= n; i++) {
  this[i] = 31
  if (i == 4 || i == 6 || i == 9 || i == 11) { this[i] = 30 }
  if (i == 2) { this[i] = 29 }
}
  return this
}
  function isDate(dtStr) {
  var daysInMonth = DaysArray(12)
  var pos1 = dtStr.indexOf(dtCh)
  var pos2 = dtStr.indexOf(dtCh, pos1 + 1)
  var strMonth = dtStr.substring(0, pos1)
  var strDay = dtStr.substring(pos1 + 1, pos2)
  var strYear = dtStr.substring(pos2 + 1)
strYr = strYear
  if (strDay.charAt(0) == "0" && strDay.length > 1)
strDay = strDay.substring(1)
  if (strMonth.charAt(0) == "0" && strMonth.length > 1)
strMonth = strMonth.substring(1)
  for (var i = 1; i <= 3; i++) {
  if (strYr.charAt(0) == "0" && strYr.length > 1)
strYr = strYr.substring(1)
}
month = parseInt(strMonth)

day = parseInt(strDay)
year = parseInt(strYr)
  if (pos1 == -1 || pos2 == -1) {
alert("The date format should be : mm/dd/yyyy")
  return false
}
  if (strMonth.length < 1 || month < 1 || month > 12) {
alert("Please enter a valid month")
  return false
}
  if (strDay.length < 1 || day < 1 || day > 31 || (month == 2 && day > daysInFebruary(year)) || day > daysInMonth[month]) {
alert("Please enter a valid day")
  return false
}
  if (strYear.length != 4 || year == 0 || year < minYear || year > maxYear) {
alert("Please enter a valid 4 digit year between " + minYear + " and " + maxYear)
  return false
}
  if (dtStr.indexOf(dtCh, pos2 + 1) != -1 || isInteger(stripCharsInBag(dtStr, dtCh)) == false) {
alert("Please enter a valid date")
  return false
}
  return true
}
  function ValidateForm() {
  var dt;
dt = document.getElementById('txtDate');
  if (isDate(dt.value) == false) {
dt.focus()
  return false
}
  return true
}
</script>
</head>
<body>
   <form id="form2" runat="server">
   <div>
  <asp:TextBox ID="txtDate" runat="server">
  </asp:TextBox>
  <asp:Button ID="Button1" runat="server" Text="Button" OnClientClick="ValidateForm()" /></div>
   </form>
</body>