如何使用onChange函数获取下拉列表的值和id并通过ajax传递

// HTML代码
<select id="mySelect" onChange="getSelectedValue()">
  <option value="1">选项1</option>
  <option value="2">选项2</option>
  <option value="3">选项3</option>
</select>

// JavaScript代码
function getSelectedValue() {
  var select = document.getElementById("mySelect");
  var selectedValue = select.options[select.selectedIndex].value;
  var selectedId = select.options[select.selectedIndex].id;

  // 使用ajax传递值和id给后端
  var xhr = new XMLHttpRequest();
  xhr.open("POST", "后端处理接口地址", true);
  xhr.setRequestHeader("Content-Type", "application/json");
  xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
      // 处理后端返回的结果
      var response = JSON.parse(xhr.responseText);
      // 进行相关操作
    }
  };
  var data = JSON.stringify({ value: selectedValue, id: selectedId });
  xhr.send(data);
}