尝试从多个选择下拉列表中添加选定项目的值

<select id="myDropdown">
  <option value="option1">选项1</option>
  <option value="option2">选项2</option>
  <option value="option3">选项3</option>
  <option value="option4">选项4</option>
</select>

var dropdown = document.getElementById("myDropdown");
var selectedValue = dropdown.options[dropdown.selectedIndex].value;

var targetDropdown = document.getElementById("targetDropdown");
var newOption = document.createElement("option");
newOption.value = selectedValue;
newOption.text = selectedValue;
targetDropdown.add(newOption);