How to acess dbRef.$id and dbRef.$ref in mongosh?

Using MongoDB: 6.0.4 Using Mongosh: 1.4.1

I inserted a book and a publisher (dbRef) with mongosh.

# insert publisher
publisher_id = ObjectId()
db.publishers.insert_one({
    '_id': publisher_id,
    'title': 'XXX',
    'website': 'https://xxxxxxx.com',
})

# insert books
db.books.insert_one({
    'title': 'Good book',
    'author': 'Someone',
    'publishers': [ 
        {
            '$ref': 'publishers',
            '$id': publisher_id, 
        },
    ], 
})

Then run the following commands with mongosh.

> var book = db.books.findOne({title:'Good book'})
> var dbRef = book.publishers[0]
> dbRef
DBRef("publishers", ObjectId("..."))

According to the link below, I think I can access $id and $ref of the dbRef object, but I got empty lines. How can I access $id and $ref with mongosh?

> dbRef.$id 
  // empty line

> dbRef.$ref
  // empty line

> dbRef.collection
publishers

> JSON.stringify(dbRef)
{"$ref":"publishers","$id":"..."}

How to show data from 2 collections in Mongodb with DBRef

UPDATE

For newer version of mongosh,

> dbRef.oid
ObjectId("...")
> dbRef.collection
publishers

For older version of mongosh,

> dbRef.toJSON().$id
ObjectId("...")

> dbRef.toJSON().$ref
publishers

DBRef is a separate data type: https://mongodb.github.io/node-mongodb-native/3.6/api/DBRef.html

new DBRef(namespace, oid, db)

Try dbRef.oid