我上传图片与ajax的帮助下，也显示在一个div，但它不会显示图像的第一次图片上传到php

<input type="file" id="uploadInput">
<div id="imageContainer"></div>

<script>
  document.getElementById('uploadInput').addEventListener('change', function() {
    var file = this.files[0];
    var formData = new FormData();
    formData.append('image', file);

    var xhr = new XMLHttpRequest();
    xhr.open('POST', 'upload.php', true);
    xhr.onload = function() {
      if (xhr.status === 200) {
        var imageUrl = xhr.responseText;
        document.getElementById('imageContainer').style.backgroundImage = 'url(' + imageUrl + ')';
      }
    };
    xhr.send(formData);
  });
</script>

<?php
  // 保存上传的图片到服务器
  $image = $_FILES['image'];
  $uploadPath = 'uploads/' . $image['name'];
  move_uploaded_file($image['tmp_name'], $uploadPath);

  // 返回图片的URL
  echo $uploadPath;
?>