JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.12.1/jquery-ui.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.12.1/jquery-ui.theme.min.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.12.1/themes/blitzer/theme.css">
<input type="hidden"...

JavaScript

$( function() {
 $('#vybersportu').change(function(){
    

function available(date) {

  var terminy = [$("#datumy").val()]; 
  
  dmy = ("0" + date.getDate()).slice(-2) + "." + ("0" + (date.getMonth() + 1)).slice(-2) + "." + date.getFullYear();

  if ($.inArray(dmy, terminy) != -1) {

    return [true, "",""];
  } else {
    return [false,"",""];
  }
}    

    $( "#datepicker" ).datepicker({ beforeShowDay: available });
  } );
    } );