/* HTML form */
<div>
 <input id="fileupload" type="file" name="fileupload" /> 
 <button onclick="uploadFile()"> Upload </button>
</div>
	

// javascript ajax when button upload clicked
<script type="text/javascript">
async function uploadFile() {
  let formData = new FormData(); 
  formData.append("file", fileupload.files[0]);
  await fetch('../post/route.php', {
    method: "POST", 
    body: formData
  }); 
  alert('The file has been uploaded successfully.');
}
</script>
	

// backend PHP
if (!empty($_FILES)) {
  $folder="/folder/upload";
  if (!is_dir($folder)) {
    mkdir($folder, 0755, true);
  }
  $filename = $_FILES['file']['name'];
  $location = $folder ."/".$filename; 

  if ( move_uploaded_file($_FILES['file']['tmp_name'], $location) ) { 
    echo 'Success'; 
  } else { 
    echo 'Failure'; 
  }
}