如何创建下拉依赖关系

<select id="firstDropdown">
  <option value="option1">Option 1</option>
  <option value="option2">Option 2</option>
  <option value="option3">Option 3</option>
</select>

<select id="secondDropdown">
  <!-- 第二个下拉列表的选项内容将根据第一个下拉列表的选择而变化 -->
</select>

document.getElementById("firstDropdown").addEventListener("change", function() {
  var firstDropdownValue = this.value;
  var secondDropdown = document.getElementById("secondDropdown");
  
  // 清空第二个下拉列表的选项内容
  secondDropdown.innerHTML = "";
  
  // 根据第一个下拉列表的选择值生成第二个下拉列表的选项内容
  if (firstDropdownValue === "option1") {
    var option1 = document.createElement("option");
    option1.value = "option1-1";
    option1.text = "Option 1-1";
    secondDropdown.appendChild(option1);
    
    var option2 = document.createElement("option");
    option2.value = "option1-2";
    option2.text = "Option 1-2";
    secondDropdown.appendChild(option2);
  } else if (firstDropdownValue === "option2") {
    var option3 = document.createElement("option");
    option3.value = "option2-1";
    option3.text = "Option 2-1";
    secondDropdown.appendChild(option3);
    
    var option4 = document.createElement("option");
    option4.value = "option2-2";
    option4.text = "Option 2-2";
    secondDropdown.appendChild(option4);
  } else if (firstDropdownValue === "option3") {
    var option5 = document.createElement("option");
    option5.value = "option3-1";
    option5.text = "Option 3-1";
    secondDropdown.appendChild(option5);
    
    var option6 = document.createElement("option");
    option6.value = "option3-2";
    option6.text = "Option 3-2";
    secondDropdown.appendChild(option6);
  }
});