nodejs function in class returns undefined - node.js

Question

So, I have a function in my class that should return an object, but instead it returns undefined, which I dont know why it is happening, here's the code:
method.getQuests = function(){
var id = this._data[0].id;
var lvl = this._data[0].level;
var structure = [];
connection.query("SELECT * FROM quest WHERE player_id = ?", [id], function(errors, rowss, fieldss) {
for(var i = 0; i < rowss.length; i++){
var rewards = {
"coins":rowss[i].gold,
"xp":rowss[i].experience,
"honor":rowss[i].honor,
"premium":rowss[i].donut,
"statPoints":0,
"item":0
};
structure.push({
"id": rowss[i].id,
"character_id": id,
"identifier": rowss[i].name,
"type": 1,
"stage": rowss[i].stage,
"level": lvl,
"status": 1,
"duration_type": 1,
"duration_raw": (rowss[i].duration * 60) * 4,
"duration": rowss[i].duration * 60,
"ts_complete": 0,
"energy_cost": rowss[i].duration,
"fight_difficulty": 0,
"fight_npc_identifier": "",
"fight_battle_id": 0,
"used_resources": 0,
"rewards": JSON.stringify(rewards)
});
}
return structure;
});
}
What is also happening is that after I call some mysql query my user data stored in this._data doesn't exist anymore, so Im totally lost at this point.

Answer 1

connection.query is async, so when you return structure; it will return undefined because the async function connection.query() hasn't completed yet. Try using a callback. When you define your function, define it like this:
method.getQuests = function(callback){
And instead of return structure; try
callback(structure);
Then, when you call it and want to use it, use it like this:
method.getQuests(function(structure){
console.log(structure);
});