在单击选择下拉菜单时添加另一个选项？

<select id="myDropdown">
  <option value="option1">选项1</option>
  <option value="option2">选项2</option>
  <option value="option3">选项3</option>
</select>

document.getElementById("myDropdown").addEventListener("click", function() {
  var newOption = document.createElement("option");
  newOption.text = "新选项";
  newOption.value = "newOption";
  this.add(newOption);
});