Pure JS realizes the effect of the drop-down menu of date of birth [year, month and day]

function DateSelector(selYear, selMonth, selDay) {//Define the function   = selYear;
   = selMonth;
   = selDay;
   = this;
   = this;
// Add a function to the year and month drop-down menu to handle onchange events  if ( != null) // IE
  {
    ("onchange", );
    ("onchange", );
  }
  else // Firefox
  {
    ("change", , false);
    ("change", , false);
  }
  if ( == 4) // If the number of parameters passed is 4, the last parameter must be a Date object    (arguments[3].getFullYear(), arguments[3].getMonth() + 1, arguments[3].getDate());
  else if ( == 6) // If the number of parameters passed is 6, the last three parameters must be the initial year, month, and day values    (arguments[3], arguments[4], arguments[5]);
  else // Use the current date by default  {
    var dt = new Date();
    ((), () + 1, ());
  }
}
// Add an attribute of the smallest year - the oldest = 1960;
// Add the attribute of the largest year - the latest year, that is, the current period getFullYear() = (new Date()).getFullYear();
// Initialize year = function () {
// Loop to add OPION elements to the year select object  for (var i = ; i >= ; i--) {
// Create a new OPTION object    var op = ("OPTION");
// Set the value of the OPTION object     = i;
// Set the contents of the OPTION object     = i;
// Add to year select object    (op);
  }
}
// Initialize the month = function () {
// Loop to add OPION elements to month select object  for (var i = 1; i < 13; i++) {
// Create a new OPTION object    var op = ("OPTION");
// Set the value of the OPTION object     = i;
// Set the contents of the OPTION object     = i;
// Add to month select object    (op);
  }
}
// Get the number of days of the month based on year and month = function (year, month) {
  var date = new Date(year, month, 0);
  return ();
}
// Initialization days = function () {
// Use parseInt function to get the current year and month  var year = parseInt();
  var month = parseInt();
// Get the number of days in the month  var daysInMonth = (year, month);
// Clear the original options   = 0;
// Loop to add OPION elements to the day select object  for (var i = 1; i <= daysInMonth; i++) {
// Create a new OPTION object    var op = ("OPTION");
// Set the value of the OPTION object     = i;
// Set the contents of the OPTION object     = i;
// Add to the days select object    (op);
  }
}
// Method for handling year and month onchange events, which gets the event source object (i.e. selYear or selMonth)// and call its Group object (i.e. DateSelector instance, see constructor) to reinitialize the number of days// Parameter e is an event object = function (e) {
  var selector =  != null ?  : ;
  ();
}
// Initialize the drop-down menu option according to the parameters = function (year, month, day) {
// Since this method can be called externally, we also need to clear the options of selYear and selMonth here.// In addition, because the InitDaySelect method already has the clear number of days drop-down menu, there is no need to repeat the work here   = 0;
   = 0;
// Initialize year and month  ();
  ();
// Set the initial values ​​of year and month   =  - year;
   = month - 1;
// Initialization days  ();
// Set the initial value of the number of days   = day - 1;
}

<script type="text/javascript" src="/js/"></script>
<select ></select>Year
<select ></select>moon
<select ></select>day
<!--完成出生day期的选择--Need to be written in</body>forward-->
<script type="text/javascript">
var selYear = ("selYear");
var selMonth = ("selMonth");
var selDay = ("selDay");
// Create a new instance of the DateSelector class and pass three select objects into itnew DateSelector(selYear, selMonth, selDay, 1995, 1, 17);
</script>
</body>
</html>