My code looks like this:

1. $("#date_from, #date_to").datepicker({
       defaultDate
   : "+1d",
       minDate
   : "+1d",
       changeMonth
   : true,
       changeYear
   : true,
       dateFormat
   : "dd/mm/yy",
       monthNamesShort
   : ["Sty", "Lut", "Mar", "Kwi", "Maj", "Cze", "Lip", "Sie", "Wrz", "Paz", "Lis", "Gru"],
       dayNamesMin
   : ["Nie", "Pon", "Wt", "Śr", "Czw", "Pt", "Sob"],
       numberOfMonths
   : 1,
       constrainInput
   : true,
       beforeShowDay
   : noWeekendsOrHolidays,
       firstDay
   : 1, // Start with Monday
       onSelect
   : function (dateText, inst) {
           
   if (this.id == 'date_from') {
               
   var dateMin = $('#date_from').datepicker("getDate");
               
   var dateMax = $('#date_to').datepicker('getDate');
               
   var rent_date_from = new Date(dateMin.getFullYear(), dateMin.getMonth(), dateMin.getDate() + 1);
               
   var rent_date_to = new Date(dateMin.getFullYear(), dateMin.getMonth(), dateMin.getDate() + 29);
               $
   ('#date_to').datepicker("option", "minDate", rent_date_from);
               $
   ('#date_to').datepicker("option", "maxDate", rent_date_to);
   
           
   
   }
           $
   ('#day_of_week1').val($.datepicker.formatDate('DD', dateMin));
           $
   ('#day_of_week2').val($.datepicker.formatDate('DD', dateMax));
           compute
   (); //Add compute
       
   }
   
   
   });

For now, I get a value but only from the first field (in the #day_of_week1), but I can't get the value from the second one. I don't know where is the problem?

Thanks for any help.