ajax连接js和mysql数据库

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
  if (this.readyState === 4 && this.status === 200) {
    // 处理服务器返回的数据
    var response = JSON.parse(this.responseText);
    // 更新页面内容
    document.getElementById("result").innerHTML = response.result;
  }
};
xhttp.open("GET", "backend.php?data=" + data, true);
xhttp.send();

<?php
$data = $_GET['data'];
// 连接MySQL数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";
$conn = new mysqli($servername, $username, $password, $dbname);
// 执行数据库查询操作
$sql = "SELECT * FROM table WHERE data = '$data'";
$result = $conn->query($sql);
$response = array();
if ($result->num_rows > 0) {
  // 将查询结果存入响应数组
  while ($row = $result->fetch_assoc()) {
    $response[] = $row;
  }
} else {
  $response['result'] = "No data found";
}
$conn->close();
// 返回JSON格式的响应数据
header('Content-Type: application/json');
echo json_encode($response);
?>