Proper way to add a callback to jQuery DatePicker

Question

DatePicker has an internal function, _adjustDate(), which I'd like to add a callback after.

Current Method

---

This is how I'm currently doing this. Basically, just replacing the function defintion with itself, plus the new operations. This effects all datepickers, which I'm not sure is desired, either.

$(function(){

   var old = $.datepicker._adjustdate;

   $.datepicker._adjustDate = function(){
      old.apply(this, arguments);

      // custom callback here     
      console.log('callback');
   };

});

_adjustDate is what's called during the next/prev month clicks. The function takes three parameters. I'm curious if there's a better way to add the callback.

Expected Result

---

I'd like to have the end result look like this; where afterAjustDate is the callback handle:

$('#datepicker').datepicker({ 
       showButtonPanel: true
     , afterAdjustDate: function(){ $(this).find('foo').addClass('bar'); }
});

FYI

---

onChangeMonthYear is not an acceptable event alternative, neither are the live()/delegate() (don't work in IE) binding options.

This comes from the need of applying classes/manipulating elements after the month is selected. Changing the month recreates elements in the calendar; when this is performed jQueryUI is not smart enough to inherit the class changes. Thus, I need a callback after changing the date.

Answer 1

I wrote a small demo that does this...

I create an object literal that contains the extensions to $.datepicker and then do $.extend on $.datepicker and my object.

You can check it out here: http://jsfiddle.net/NHN4g/4/

Here's the extension itself:

(function($){
    var datepickerExtensions = {
        _oldAdjustDate: $.datepicker._adjustDate,
        _adjustDate: function(id, offset, period) { 
            var target = $(id);
            var inst = this._getInst(target[0]);
            var afterAdjustDate = this._get(inst, 'afterAdjustDate');
            this._oldAdjustDate(id, offset, period);
            if(afterAdjustDate && typeof afterAdjustDate === 'function'){
                afterAdjustDate(id, offset, period);
            }
        }
    }
    $.extend($.datepicker, datepickerExtensions);
})(jQuery);

And the demo:

(html)

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.16/themes/base/jquery-ui.css" type="text/css" media="all">
<div class="demo">
    <p>Date: <input type="text" id="datepicker"></p>
</div><!-- End demo -->

(javascript)

var changed = false;
$("#datepicker").datepicker({ 
    afterAdjustDate: function(i,o,p){
        if(!changed){
            $('.ui-datepicker-month').css('color', '#f00');
        }
        changed = !changed;
    }
});