How to get the value of children in Firebase Javascript?

This is the most basic way to show the list of image URLs:

var rootRef = firebase.database.ref();
var urlRef = rootRef.child("user1/DAA Notes/URL");
urlRef.once("value", function(snapshot) {
  snapshot.forEach(function(child) {
    console.log(child.key+": "+child.val());
  });
});