Waiting for function to finish than continue

var spotifyPlaylist = require('spotify-playlist');
var wait = require('wait.for');


var playlistSongNames = [];


Object.size = function(obj) {
    var size = 0, key;
    for (key in obj) {
        if (obj.hasOwnProperty(key)) size++;
    }
    return size;
};

let getNames = function (err, result){
    var objectPlaylist = result.playlist.tracks;
    var objectSize = Object.size (objectPlaylist);

    for (var i = 0; i != objectSize; i++){
        playlistSongNames[i] = objectPlaylist[i].name + " - " + objectPlaylist[i].artists + "\n";
    }

}

spotifyPlaylist.playlistUri('spotify:user:spotify:playlist:4hOKQuZbraPDIfaGbM3lKI', getNames);
console.log (playlistSongNames);

I wanna be able to wait for playListSongNames to finish and then continue with the program

(As an example console.log (playListSongNames))

via Jamie Stivala