如何将targetdestination发送到php变量

<form id="myForm">
  <input type="text" id="targetDestination" name="targetDestination">
  <button type="submit">提交</button>
</form>

<script>
  document.getElementById("myForm").addEventListener("submit", function(event) {
    event.preventDefault(); // 阻止表单默认提交行为

    var targetDestination = document.getElementById("targetDestination").value;

    // 使用AJAX请求将目标目的地的值发送到PHP文件
    var xhr = new XMLHttpRequest();
    xhr.open("POST", "backend.php", true);
    xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4 && xhr.status === 200) {
        console.log(xhr.responseText);
      }
    };
    xhr.send("targetDestination=" + encodeURIComponent(targetDestination));
  });
</script>

<?php
  $targetDestination = $_POST["targetDestination"]; // 接收目标目的地的值

  // 将接收到的目标目的地的值赋给PHP变量
  $phpVariable = $targetDestination;

  // 进行其他操作，如数据库查询、数据处理等

  echo "目标目的地已发送到PHP变量：".$phpVariable;
?>