javascrip在codeigniter中获取dropdown的值

function getDropdownValue() {
  var dropdown = document.getElementById("myDropdown");
  var dropdownValue = dropdown.value;
  // 可以在此处对dropdownValue进行其他操作
}

var dropdown = document.getElementById("myDropdown");
dropdown.addEventListener("change", getDropdownValue);

<form action="your_controller/action" method="post">
  <select id="myDropdown" name="myDropdown">
    <option value="option1">Option 1</option>
    <option value="option2">Option 2</option>
    <option value="option3">Option 3</option>
  </select>
  <input type="hidden" id="dropdownValue" name="dropdownValue">
  <button type="submit">Submit</button>
</form>

function getDropdownValue() {
  var dropdown = document.getElementById("myDropdown");
  var dropdownValue = dropdown.value;
  document.getElementById("dropdownValue").value = dropdownValue;
}