JSFiddle - React, Tailwind, and code Playground

HTML

<select id="opstina">
  <option value="volvo">Volvo</option>
  <option value="saab">Saab</option>
  <option value="mercedes">Mercedes</option>
  <option value="audi">Audi</option>
</select>

JavaScript

if ($("#opstina option:selected").length) {
            $("select#mesto").attr("disabled","disabled");
            $("select#mesto").html("<option>wait...</option>");
            var id= $("select#opstina option:selected").attr('value'); // Ovo je ta linija koja je problem
            alert(id);
            $.post("select_mesto.php", {id:id}, function(data){
                $("select#mesto").removeAttr("disabled");
                $("select#mesto").html(data);
            });
        }