query of is document exists firebase js code example

Example 1: 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()))

Example 2: get data from firestore

const [hospitalsDetails, setHospitalsDetails] = useState([])
    useEffect(()=>{
        //load hospitals into hospitalsList
        const hospitals = []
        db.collection('Hospitals').get()
            .then(snapshot => {
                snapshot.docs.forEach(hospital => {
                    let currentID = hospital.id
                    let appObj = { ...hospital.data(), ['id']: currentID }
                    hospitals.push(appObj)

                    hospitals.push(hospital.data())
            })
            setHospitalsDetails(hospitals)
        })
    },[])