如何在原始文件上传中显示maxFileSize消息？

<form action="/upload" method="post" enctype="multipart/form-data">
  <input type="file" name="file" id="fileInput">
  <button type="submit">上传文件</button>
</form>
<div id="errorMsg"></div>

<script>
  document.querySelector('form').addEventListener('submit', function(e) {
    e.preventDefault();
    var fileInput = document.getElementById('fileInput');
    var file = fileInput.files[0];
    var maxFileSize = 10 * 1024 * 1024; // 10MB

    if (file.size > maxFileSize) {
      document.getElementById('errorMsg').textContent = '文件大小超过限制';
    } else {
      // 文件上传逻辑
      this.submit();
    }
  });
</script>

const express = require('express');
const multer = require('multer');

const app = express();
const upload = multer({ dest: 'uploads/' });

app.post('/upload', upload.single('file'), (req, res) => {
  const file = req.file;
  const maxFileSize = 10 * 1024 * 1024; // 10MB

  if (file.size > maxFileSize) {
    res.status(400).json({ error: '文件大小超过限制' });
  } else {
    // 文件上传逻辑
    res.json({ message: '文件上传成功' });
  }
});

app.listen(3000, () => {
  console.log('服务器已启动');
});