通过ajax formData请求上传laravel中的.temp文件时，仅保存.pdf扩展文件

// HTML部分
<form id="uploadForm" enctype="multipart/form-data">
  <input type="file" name="file" id="fileInput">
  <button type="submit">上传</button>
</form>

// JavaScript部分
<script>
  document.getElementById('uploadForm').addEventListener('submit', function(e) {
    e.preventDefault();
    
    var fileInput = document.getElementById('fileInput');
    var file = fileInput.files[0];
    
    var formData = new FormData();
    formData.append('file', file);
    
    // 发送AJAX请求
    var xhr = new XMLHttpRequest();
    xhr.open('POST', '/upload', true);
    xhr.onreadystatechange = function() {
      if (xhr.readyState === 4 && xhr.status === 200) {
        // 上传成功
        console.log(xhr.responseText);
      }
    };
    xhr.send(formData);
  });
</script>

public function upload(Request $request)
{
    $file = $request->file('file');
    $extension = $file->getClientOriginalExtension();
    
    if ($extension === 'pdf') {
        $filename = $file->store('pdfs');
        // 保存成功
        return response()->json(['message' => '文件上传成功', 'filename' => $filename]);
    } else {
        // 扩展名不是.pdf，不保存文件
        return response()->json(['message' => '只能上传.pdf文件']);
    }
}