I have 2 datepickers - date from and date to, something like hotel reservation system. How do I check (and show hidden div.error) if there are some disabled days in selected period?

Ex. - selected dates - from 2021-12-20 to 2021-12-31; disabled days are ["2021-12-25", "2021-12-26"] -> show "error".

<div class="error" style="display:none">Sorry, but we have no available rooms in selected dates.</div>

<script>
$( function() {
                var disableddates = ["2021-12-25", "2021-12-26"];
                
                $.datepicker.setDefaults($.datepicker.regional["de"]);
                $( "#from" ).datepicker({          
                beforeShowDay: function(date){
                    var string = jQuery.datepicker.formatDate("yy-mm-dd", date);
                    return [ disableddates.indexOf(string) == -1 ]
                    }
                });
                
                $( "#to" ).datepicker({     
                beforeShowDay: function(date){
                    var string = jQuery.datepicker.formatDate("yy-mm-dd", date);
                    return [disableddates.indexOf(string) == -1 ]
                    }
                });
            });
</script>