JSFiddle - React, Tailwind, and code Playground

HTML

<div class="demo">

<p>Date: <input type="text" id="datepicker"></p>

</div><!-- End demo -->

JavaScript

(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){
                afterAdjustDate(id, offset, period);
            }
        }
    }
    $.extend($.datepicker, datepickerExtensions);
})(jQuery);

$( "#datepicker" ).datepicker({ 
    afterAdjustDate: function(i,o,p){
        alert('works');
    }
});