根据复选框更改下拉值

<input type="checkbox" id="checkbox" onchange="updateDropdown()">
<select id="dropdown">
  <option value="option1">选项1</option>
  <option value="option2">选项2</option>
  <option value="option3">选项3</option>
</select>

function updateDropdown() {
  var checkbox = document.getElementById("checkbox");
  var dropdown = document.getElementById("dropdown");
  
  if (checkbox.checked) {
    dropdown.options[0].text = "新选项1";
    dropdown.options[1].text = "新选项2";
    dropdown.options[2].text = "新选项3";
  } else {
    dropdown.options[0].text = "选项1";
    dropdown.options[1].text = "选项2";
    dropdown.options[2].text = "选项3";
  }
}