printSet.js

const result = await DynamoDB.get({
   TableName,
   Key: { id: "1234" }
 }).promise();
 console.log(result.Item.friends);
 console.log(Array.isArray(result.Item.friends.values));

// Output:
Set {
  wrapperName: 'Set',
  values: [ 'frylock', 'meatwad', 'shake' ],
  type: 'String' }
true