merelyJunior

$(".nav-link").one('click', function () {
    event.preventDefault();
    req.abort();
    $(".nav-link").click();
});

const fieldset = document.getElementById("#fieldset");
if (fieldset) {
    document.getElementById("postButton").removeAttribute("disabled");
} else {

$("#form").on("submit", function (event) {
  event.preventDefault();
  const fieldset = document.getElementById("#fieldset");
  if (fieldset) {
    $.ajax({
      url: "",
      type: "POST",
      contentType: "application/json",
      data: form.toJson(),
    })
  }
});

функция_которая_добавляет_fieldset_ы() {
  //...
  document.getElementById("postButton").removeAttribute("disabled");
}