Spotify Apps API - Get a user's listening history from Facebook (JS)

spotify-apps-sandbox-Facebook_get_listening_history.js

/* Instantiate the global sp object; include models & views */
var sp = getSpotifyApi(1);
var auth = sp.require('sp://import/scripts/api/auth');

var permissions = ['user_actions.music'];
var app_id = '126891607432106';
var request_url = 'https://graph.facebook.com/me/music.listens';

auth.authenticateWithFacebook(app_id, permissions, {
    onSuccess : function(accessToken, ttl) {
        var url = request_url + '?access_token=' + accessToken;
        $.getJSON(url, function(data) {
            var listens = data.data;
            for(var i=0;i<listens.length;i++) {
                var tracklink = listens[i].data.song.url;
                var trackname = listens[i].data.song.title;
                $('#listens').append('<li><a href="' + tracklink + '">' + trackname + '</a></li>');
            }
        });
    },
    onFailure : function(error) {
        console.log("Authentication failed with error: " + error);
    },
    onComplete : function() { }
});

Thanks for this! Going to play around...Does this always work? What if a user doesn't post their song to Facebook?