Firebase promise - Query.once failed: Was called with 1 argument. Expects at least 2

Question

I'm trying to fill an array with some data from Firebase using promises. Here's the DB structure:

- domain name(or something)
  |--highscore
     |--Foo: 50
     |--Bar: 60

The code:

var arr=[];
highscoreRef.child('highscore').once('value').then(function(snapshot) {
    snapshot.forEach(function(data) {
    arr.push({playerName: data.key(), score: data.val()});
    });
  }, function(error) {
     console.error(error);
});

I get Uncaught Error: Query.once failed: Was called with 1 argument. Expects at least 2.

Does that mean I have to add at least 2 properties to Foo and Bar? Ex. Foo = {playerName: name, score: 50}

The current DB arrangement fits my needs.

Answer 1

This error message happens when you try to use the Promisified API on a pre-Promisified SDK.

Callbacks (that other answers have suggested) will work on any 2.x version of the Firebase SDK.

We introduced an alternative syntax using promises in Firebase's JavaScript SDK version 2.4. See an example of once().then() in this jsbin: http://jsbin.com/qiranu/edit?js,console

Are you using Firebase JavaScript SDK version 2.4 or later (that's where promises were introduced)?