如何将下拉选择中的隐藏值传递给表单？

<select id="mySelect">
  <option value="1">选项1</option>
  <option value="2">选项2</option>
  <option value="3">选项3</option>
</select>

<input type="hidden" id="hiddenInput" name="hiddenInput">

document.getElementById("mySelect").addEventListener("change", function() {
  var selectedValue = this.value;
  document.getElementById("hiddenInput").value = selectedValue;
});