Node JS REST API镜像上传，如何只上传jpg文件而不上传png文件？

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

const app = express();

// 设置文件上传的存储位置和文件名
const storage = multer.diskStorage({
  destination: function (req, file, cb) {
    cb(null, 'uploads/');
  },
  filename: function (req, file, cb) {
    cb(null, file.originalname);
  }
});

// 创建multer实例
const upload = multer({ storage: storage });

// 定义上传接口
app.post('/upload', upload.single('image'), function (req, res, next) {
  // 获取上传的文件信息
  const file = req.file;

  // 判断文件扩展名是否为jpg
  const extname = path.extname(file.originalname);
  if (extname === '.jpg') {
    // 将文件保存到指定位置
    fs.renameSync(file.path, 'uploads/' + file.originalname);
    res.send('File uploaded successfully.');
  } else {
    // 删除不符合条件的文件
    fs.unlinkSync(file.path);
    res.send('Only JPG files are allowed.');
  }
});

// 启动服务器
app.listen(3000, function () {
  console.log('Server is running on port 3000');
});