Firebase, Retrieving Data Asynchronously

I wrote a promise in javascript to delay an animation until some data is retrieved from my firebase database. The problem is that for some reason the promise isn't working, and the

Solution 1:

The first problem is that (as I commented on cartant's answer) an on() handler can be invoked multiple times and thus cannot be treated as a promise.

If you only care about the current value of the node, you can use once(), which does return a promise:

var name = document.querySelector('.name')

firebase.database().ref('users/' + userId ).once('value', function(snap) {
    console.log('first');   
    name.innerText = snap.child('name').val();
}).then(function() { console.log('second') });

Alternatively, if you do care about changes in the value too, you may want to keep on using on(). But in that case you should pass in a callback.

var name = document.querySelector('.name')

firebase.database().ref('users/' + userId ).on('value', function(snap) {
    console.log('first');   
    name.innerText = snap.child('name').val();
});

If you want to explicitly detect the first value in this, do something like:

var name = document.querySelector('.name'),
    isFirst = true;

firebase.database().ref('users/' + userId ).on('value', function(snap) {
    console.log('first');   
    name.innerText = snap.child('name').val();
    if (isFirst) {
        console.log('second');
    }
    isFirst = false;
});