async function gatherFilesInfo(postId, fileInputs) {
  const postRef = doc(db, 'posts', postId);
  const postSnapshot = await getDoc(postRef);
  if (!postSnapshot.exists()) {
    console.error('Document does not exist!');
    return [];
  }

  const postData = postSnapshot.data();
  let existingFiles = postData.files || [];
  let newFilesData = existingFiles.map(file => ({ ...file }));

  for (let i = 0; i < fileInputs.length; i++) {
    const fileInput = fileInputs[i];
    if (fileInput && fileInput.files && fileInput.files.length > 0) {
      const file = fileInput.files[0];
      const storageRef = ref(storage, `posts/${postId}/files/${file.name}`);
      const uploadResult = await uploadBytes(storageRef, file);
      const newUrl = await getDownloadURL(uploadResult.ref);
      newFilesData[i] = { name: file.name, url: newUrl, isEmpty: false };
    } else {
      if (!existingFiles[i] || existingFiles[i].isEmpty) {
        newFilesData[i] = { name: 'nofile', url: '', isEmpty: true };
      }
    }
  }
}

    <div class="fileup">
          <label for="file1">· paper </label>
          <input type="file" id="file1" class="file-input"/>
          <span id="file-name1" style="color: blue;">nofilenow</span>
          <span id="refile-name1" style="display: none; color: red;"></span>
          <label for="file1" class="file-label">upload</label>
        </div> //it has 0~17 number