<select id="domain" name="domain_name" class="form-group form-control">
            <option id="first_domain" value="" selected disabled>Alan Adı</option>
              <option>Deneme Değeri</option>
              <option>Sample Value</option>
              <option>Third Sample Value</option>
          </select>


<script>
    $('#domain').change(function () {
        $.post("www.SITEADRESS.com/post.php", {
            authenticity_token: "<%= form_authenticity_token.to_s %>"
        })
            .done(function (response) {
                $('#departments').find('option').not(':first').remove();
                response.data.data.forEach(function (element) {
                  $('#first_department').after("<option value='" + element.id + "'>" + element.name + "</option>");
                });
            })
            .fail(function (xhr, status, error) {
                alert("Gönderme İşleminde sorun oluştu, lütfen sistem yöneticiniz ile görüşünüz. Hata Bilgisi: " + error);
            });

    });
</script>