如何在使用php的ajax函数中以数组的形式获取选择框的数组值

<select id="mySelect" multiple>
  <option value="value1">Option 1</option>
  <option value="value2">Option 2</option>
  <option value="value3">Option 3</option>
</select>

var selectBox = document.getElementById("mySelect");
var selectedValues = [];
for (var i = 0; i < selectBox.options.length; i++) {
  if (selectBox.options[i].selected) {
    selectedValues.push(selectBox.options[i].value);
  }
}

var xhr = new XMLHttpRequest();
xhr.open("POST", "your_php_script.php", true);
xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    // 处理服务器返回的响应数据
    console.log(xhr.responseText);
  }
};
xhr.send("selectedValues=" + JSON.stringify(selectedValues));

$selectedValues = json_decode($_POST["selectedValues"]);
// 处理选择框的数组值，例如打印每个选项的值
foreach ($selectedValues as $value) {
  echo $value . "<br>";
}