从表单ListBox中选择一个值并显示关联的值

<select id="listBox" onchange="showAssociatedValue()">
  <option value="value1">选项1</option>
  <option value="value2">选项2</option>
  <option value="value3">选项3</option>
</select>

<input type="text" id="associatedValue" readonly>

function showAssociatedValue() {
  var listBox = document.getElementById("listBox");
  var associatedValue = document.getElementById("associatedValue");

  // 获取选中的值
  var selectedValue = listBox.value;

  // 根据选中的值显示关联的值
  switch (selectedValue) {
    case "value1":
      associatedValue.value = "关联值1";
      break;
    case "value2":
      associatedValue.value = "关联值2";
      break;
    case "value3":
      associatedValue.value = "关联值3";
      break;
    default:
      associatedValue.value = "";
      break;
  }
}