如何使用multerS3将文件类型限制为仅限图像？

const aws = require('aws-sdk');
const multer = require('multer');
const multerS3 = require('multer-s3');

aws.config.update({
  secretAccessKey: 'YOUR_SECRET_ACCESS_KEY',
  accessKeyId: 'YOUR_ACCESS_KEY_ID',
  region: 'YOUR_REGION'
});
const s3 = new aws.S3();

const fileFilter = (req, file, cb) => {
  if (file.mimetype.startsWith('image/')) {
    cb(null, true);
  } else {
    cb(new Error('File type not supported!'), false);
  }
};

const upload = multer({
  storage: multerS3({
    s3: s3,
    bucket: 'YOUR_S3_BUCKET_NAME',
    acl: 'public-read',
    fileFilter: fileFilter,
    metadata: (req, file, cb) => {
      cb(null, {fieldName: file.fieldname});
    },
    key: (req, file, cb) => {
      cb(null, Date.now().toString() + '-' + file.originalname);
    }
  })
});

app.post('/upload', upload.single('image'), (req, res) => {
  res.send('File uploaded successfully!');
});