get collection from document firestore code example

Example 1: collection get firesotre

async getMarker() {
    const snapshot = await firebase.firestore().collection('events').get()
    return snapshot.docs.map(doc => doc.data());
}

Example 2: get one document based on id in firestore

//retrieve one document and save it to userDetails
const [userDetails, setUserDetails] = useState('')
db.collection('users').doc(id).get()
        .then(snapshot => setUserDetails(snapshot.data()))