javascript - returning array after finish reading from Firebase

Question

I want to push all values that satisfy a certain condition to an array then return this array. Here's my code

exports.getNearbyPosts = function (myLat, myLng){
  var query = firebase.database().ref("posts/").orderByKey();
  var listOfItems = [];
  query.once("value")
    .then(function(snapshot) {
      snapshot.forEach(function(childSnapshot) {
        var key = childSnapshot.key;
        var childData = childSnapshot.val();
        var dist = getDistanceBetweenCoord(childData.lat, childData.lng, myLat, myLng);
        if(dist < 10239820938502){
          listOfItems.push(childSnapshot);
        }
    });
  });

  return listOfItems;
}

However since forEach is asynchronous, and it seems like I cannot use a callback on forEach, the listOfItems I return would just be an empty array. I have also tried ".then", but it would only allow me to do more stuff inside ".then" and I would like to return this array as a variable to other parts of the code. How can I return the correct array after forEach has been executed?

Answer 1

Waitting for answers