How do I specify the download directory in multer-S3 for an AWS-S3 bucket?

I am using express + multer-s3 to upload files to AWS S3 service.

Using the following code, I was able to load files into the S3 Bucket , but right into the bucket.

I want them to be loaded into a folder inside the bucket.

I was unable to find a way to do this.

Here is the code

AWS.config.loadFromPath("path-to-credentials.json");
var s3 = new AWS.S3();

var cloudStorage = multerS3({
    s3: s3,
    bucket: "sample_bucket_name",
    contentType: multerS3.AUTO_CONTENT_TYPE,
    metadata: function(request, file, ab_callback) {
        ab_callback(null, {fieldname: file.fieldname});
    },
    key: function(request, file, ab_callback) {
        var newFileName = Date.now() + "-" + file.originalname;
        ab_callback(null, newFileName);
    },
});
var upload = multer({
    storage: cloudStorage
});

router.post("/upload", upload.single('myFeildName'), function(request, response) {
    var file = request.file;
    console.log(request.file);
    response.send("aatman is awesome!");
});