Gagal upload gambar dengan multer di node js

Saya bikin fitur upload menggunakan multer dan ini kodenya di file routenya

// Set storage engine
const storage = multer.diskStorage({
	destination: './public/',
	filename: function(req, file, cb){
		cb(null, file.fieldname + '-' + Date.now() + path.extname(file.originalname));
	}
});

//Init upload
const upload = multer({
	storage: storage
}).single('gambar');

router.post('/avatar', (req, res) => {
	upload(req, res, (err) => {
		if(err){
			res.render('user/avatar', {
				judul: 'Ganti Avatar',
				css: '/public/css/avatar-change.css',
				msg: err
			})
		}else{
			console.log(req.file);
			res.send('success');
		}
	});
});

dan ini formnya

<form action="/user/avatar" method="post" enctype="multipart/form-data">
			<input type="file" name="gambar" id="img">
			<span><label for="img" class="btn btn-info">Pilih Gambar</label><br><a href="/user" class="btn btn-danger mr-1">Batal</a><button type="submit" class="btn btn-success ml-1">Upload</button></span>
</form>

saya coba upload gambar tapi gambarnya tidak masuk folder (tidak ada), dan hasil console.log(req.file) undefined. itu kenapa yah ?