如何从反应本机函数返回值？

Question

I want this function to return boolean from this function but I am unable to do so. I am a newbie in react native and javascript.

  checkBlocked(userId) {

    firebase.database().ref('Blocked/' + firebase.auth().currentUser.uid)
    .orderByChild('uid').equalTo(userId).once('value').then(snapshot => {

        if (snapshot.exists()){
          var isBlocked = true;
        }
      else {
       var isBlocked = false;
      }
      })

      return isBlocked;

    }

Answer 1

checkBlocked = async userId => {
  try {
  let snapshot = await firebase.database().ref('Blocked/' + firebase.auth().currentUser.uid).orderByChild('uid').equalTo(userId).once('value')
    return snapshot.exists();
  }
  catch(error) {
    return false;
  }
}