how to get collection of collection in firebase code example

Example 1: firestore get all documents in collection

// retrieve a collection
db.collection('documents')
  .get()
  .then(querySnapshot => {
    const documents = querySnapshot.docs.map(doc => doc.data())
    // do something with documents
  })

// retrieve a document
db.collection('documents')
  .doc(documentId)
  .get()
  .then(snapshot => {
    const document = snapshot.data()
    // do something with document
  })

Example 2: get data in from a collection firestore

db.collection("users").get().then((querySnapshot) => {
    querySnapshot.forEach((doc) => {
        console.log(`${doc.id} => ${doc.data()}`);
    });