javascript ile dropdown secimine göre alan gösterimi

@Html.DropDownList("optionId", new SelectList(SelectListData), "Select an option")

@Html.TextBox("controlId")

<script>
  $("#optionId").on("change", function () {
    if ($("#optionId option:selected").index() == 0) {
      $("#controlId").hide();
    } else {
      $("#controlId").show();
    }
  });
</script>