function isValidDate(dateStr, format)

{
   if (format == null) { format = “MDY”; }
   format = format.toUpperCase();
   if (format.length != 3) { format = “MDY”; }
   if ( (format.indexOf(“M”) == -1) || (format.indexOf(“D”) == -1) || _
      (format.indexOf(“Y”) == -1) ) { format = “MDY”; }
   if (format.substring(0, 1) == “Y”) { // If the year is first
      var reg1 = /^\d{2}(\-|\/|\.)\d{1,2}\1\d{1,2}$/
      var reg2 = /^\d{4}(\-|\/|\.)\d{1,2}\1\d{1,2}$/
   } else if (format.substring(1, 2) == “Y”) { // If the year is second
      var reg1 = /^\d{1,2}(\-|\/|\.)\d{2}\1\d{1,2}$/
      var reg2 = /^\d{1,2}(\-|\/|\.)\d{4}\1\d{1,2}$/
   } else { // The year must be third
      var reg1 = /^\d{1,2}(\-|\/|\.)\d{1,2}\1\d{2}$/
      var reg2 = /^\d{1,2}(\-|\/|\.)\d{1,2}\1\d{4}$/
   }
   // If it doesn’t conform to the right format (with either a 2 digit year or 4 digit year), fail
   if ( (reg1.test(dateStr) == false) && (reg2.test(dateStr) == false) ) { return false; }
   var parts = dateStr.split(RegExp.$1); // Split into 3 parts based on what the divider was
   // Check to see if the 3 parts end up making a valid date
   if (format.substring(0, 1) == “M”) { var mm = parts[0]; } else _
      if (format.substring(1, 2) == “M”) { var mm = parts[1]; } else { var mm = parts[2]; }
   if (format.substring(0, 1) == “D”) { var dd = parts[0]; } else _
      if (format.substring(1, 2) == “D”) { var dd = parts[1]; } else { var dd = parts[2]; }
   if (format.substring(0, 1) == “Y”) { var yy = parts[0]; } else _
      if (format.substring(1, 2) == “Y”) { var yy = parts[1]; } else { var yy = parts[2]; }
   if (parseFloat(yy) <= 50) { yy = (parseFloat(yy) + 2000).toString(); }
   if (parseFloat(yy) <= 99) { yy = (parseFloat(yy) + 1900).toString(); }
   var dt = new Date(parseFloat(yy), parseFloat(mm)-1, parseFloat(dd), 0, 0, 0, 0);
   if (parseFloat(dd) != dt.getDate()) { return false; }
   if (parseFloat(mm)-1 != dt.getMonth()) { return false; }
   return true;
}

————————————

The function returns true if the date is valid and false if it is not. So, your validation could look something like:

if (!isValidDate(myDateString, “DMY”)) { alert(“The date is not in the correct format.”); }