How to return the inserted item in dynamoDB

The link you posted is, sadly, the only real answer at this time (API Version 2012-08-10). PutItem may return items just before they were updated or none at all.

The ReturnValues parameter is used by several DynamoDB operations; however, PutItem does not recognize any values other than NONE or ALL_OLD.

In short, the only reliable way to retrieve your inserted object is to GetItem, just as you surmised.

Just pass the params.Item in the callback :

 dynamo.put(params, (err, data) => {
        if (err) {
          cb(err);
        }
        cb(null, params.Item);
      });

Pass the err in the callback too ;)