PHP 检测 Fetch Api 与 XMLHttpRequest

截至目前，我的网站正在使用 jQuery Ajax 从前端向后端发出请求，然后后端通过检查 $_SERVER['HTTP_X_REQUESTED_WITH']=="XMLHttpRequest" 来确定 ajax 请求。我正在尝试仅切换到本机 JS，并且想要使用 Fetch Api。问题是我似乎无法检测 PHP 中的 fetch api 请求与常规页面加载请求。 $_SERVER['HTTP_X_REQUESTED_WITH'] 显然不再起作用了。所以我尝试设置新的标头（{HTTP_X_REQUESTED_WITH}）。然后还是不行。感谢任何帮助，谢谢

JS:

let dataForm = new FormData(),
    reqHeaders = new Headers({
      "X-Custom-Header": "ThisMeansAjaxRequest",
    });

  dataForm.append('postFavColor', 'green');

  let result = fetch('/ajax/', {
    method: 'POST',
    header: reqHeaders,
    body: dataForm
  })
  .then(res=>{
    if('json' in res){
      return res.json()
    }
    throw new Error('Not so JSON');
  })
  .then(res=>{
    if (res.status === 'success') {
      // WE MADE IT!!!
      console.log(req);
      return res.message
    }
    else{
      throw new Error('Server returned Error', res)
    }
  })
  .catch(err=>{
    console.error('fetch error of some sort', err);
  });

PHP:

    // Below if statment was being used for Ajax request test from jQuery
// replacing the if statement below with the custom header passed from fetch api
// still doesn't work. Tried all 4 versions below
// if (isset($_SERVER['X_Custom_Header']) && $_SERVER['X_Custom_Header']=="ThisMeansAjaxRequest")
// if (isset($_SERVER['Custom_Header']) && $_SERVER['Custom_Header']=="ThisMeansAjaxRequest")
// if (isset($_SERVER['HTTP_X_Custom_Header']) && $_SERVER['HTTP_X_Custom_Header']=="ThisMeansAjaxRequest")
// if (isset($_SERVER['HTTP_Custom_Header']) && $_SERVER['HTTP_Custom_Header']=="ThisMeansAjaxRequest")


//// Original jquery Ajax detector
if (isset($_SERVER['HTTP_X_REQUESTED_WITH']) && $_SERVER['HTTP_X_REQUESTED_WITH']=="XMLHttpRequest") {
        //continue;
        //echo 'This is certified Ajax request <br>';
    $data = array(
            'status' => 'success',
            'message' => 'You\'re a Wizzard Harry!'
        );

        echo json_encode($data);
}
        else{
    //Not ajax request so display page
        header("location: www.example.com/index.php");
}