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 ;)

You can use UpdateItem instead of PutItem. UpdateItem creates a new item if it doesn't exist already, plus you can set ReturnValues to ALL_NEW to return the whole item as it appears in the database after the operation:

const params = {    TableName: "event",    Key: {        "eventId": date + '-' + eventName + '-' + eventPurpose    },    UpdateExpression: "SET eventName = :eventName, eventPurpose = :eventPurpose, eventDates = :eventDates, attendees = :attendees",    ExpressionAttributeValues: {        ":eventName": eventName,        ":eventPurpose": eventPurpose,        ":eventDates": eventDates,        ":attendees": attendees    },    ReturnValues: "ALL_NEW"};

Using GetItem right after PutItem is not a good idea unless you are using strong consistency in DynamodDB. If you have eventual consistency (default) then GetItem right after PutItem can still return empty.