如何根据表值填充单元格内下拉列表？

<table>
  <tr>
    <td>
      <select id="dropdown"></select>
    </td>
  </tr>
</table>

var dropdown = document.getElementById("dropdown");
var cell = dropdown.parentElement;
var row = cell.parentElement;
var rowIndex = row.rowIndex;
var columnIndex = cell.cellIndex;

function populateDropdown() {
  // 获取表格对象
  var table = document.getElementsByTagName("table")[0];

  // 清空下拉列表
  dropdown.innerHTML = "";

  // 获取所有行，跳过表头
  var rows = table.getElementsByTagName("tr");
  for (var i = 1; i < rows.length; i++) {
    // 获取当前行的单元格
    var cells = rows[i].getElementsByTagName("td");

    // 获取当前单元格的值
    var value = cells[columnIndex].innerHTML;

    // 创建下拉列表选项
    var option = document.createElement("option");
    option.text = value;

    // 添加选项到下拉列表
    dropdown.add(option);
  }
}

window.onload = populateDropdown;