Drupal 6 datepicker, blocking out weekends and certain holidays

Question

A friend of mine has a Drupal 6 site where users are able to select a future date for a delivery. Recently, several customers have been selecting weekends and holidays for delivery dates, and my friend would like to prevent them from doing so.

This is the code we're currently using to block out weekends. Can someone help modify it to also block out Christmas and New Years Eve?

Thanks very much!

drupal_add_js("
Drupal.behaviors.date_popup = function (context) {
  for (var id in Drupal.settings.datePopup) {
    $('#'+ id).bind('focus', Drupal.settings.datePopup[id], function(e) {
      if (!$(this).hasClass('date-popup-init')) {
        var datePopup = e.data;

                        // CUSTOM
        datePopup.settings.beforeShowDay = function(date) { 
   var day = date.getDay(); 
   return [(day != 0 && day != 6), '']; 
   
  }
       
        // Explicitely filter the methods we accept.
        switch (datePopup.func) {
          case 'datepicker':
            $(this)
              .datepicker(datePopup.settings)
              .addClass('date-popup-init')
            $(this).click(function(){
              $(this).focus();
            });
            break;

          case 'timeEntry':
            $(this)
              .timeEntry(datePopup.settings)
              .addClass('date-popup-init')
            $(this).click(function(){
              $(this).focus();
            });
            break;
        }
      }
    });
  }
};
    ",'inline');

UPDATE:

I ended up doing the following, which works for our needs:

drupal_add_js("
Drupal.behaviors.date_popup = function (context) {
  for (var id in Drupal.settings.datePopup) {
    $('#'+ id).bind('focus', Drupal.settings.datePopup[id], function(e) {
      if (!$(this).hasClass('date-popup-init')) {
        var datePopup = e.data;

         // CUSTOM
  
  datePopup.settings.beforeShowDay = function(date) {
        var day = date.getDay(), Sunday = 0, Monday = 1, Tuesday = 2, Wednesday = 3, Thursday = 4, Friday = 5, Saturday = 6;
        var closedDates = [[12, 31, 2015], [12, 25, 2015]];
        var closedDays = [[Saturday], [Sunday]];
        for (var i = 0; i < closedDays.length; i++) {
            if (day == closedDays[i][0]) {
                return [false];
            }

        }

        for (i = 0; i < closedDates.length; i++) {
            if (date.getMonth() == closedDates[i][0] - 1 &&
            date.getDate() == closedDates[i][1] &&
            date.getFullYear() == closedDates[i][2]) {
                return [false];
            }
        }

        return [true];
    }
       
        // Explicitely filter the methods we accept.
        switch (datePopup.func) {
          case 'datepicker':
            $(this)
              .datepicker(datePopup.settings)
              .addClass('date-popup-init')
            $(this).click(function(){
              $(this).focus();
            });
            break;

          case 'timeEntry':
            $(this)
              .timeEntry(datePopup.settings)
              .addClass('date-popup-init')
            $(this).click(function(){
              $(this).focus();
            });
            break;
        }
      }
    });
  }
};
    ",'inline');