Pushing Mongoose Results into Array - node.js

Question

I am trying to get results from my "Books.find" and push it into my books array. I want to then res.send it.
I suspect this has something to do with some kind of asynchronous and scope rubbish.
What's the solution?
This is currently my code.
exports.timeline = function(req, res) {
var Followers = mongoose.model('Follow');
Followers.find({'follower': req.user.username}, function(err, followerResult) {
var name = [req.user.username];
var books = [];
function addName(username) {
name.push(username);
}
for(var user in followerResult) {
addName(followerResult[user]['followed']);
}
function getDataByUsername(username) {
function addBookArray(result) {
books.push(result);
return result;
}
var Books = mongoose.model('Book');
Books.find({'username': username}).exec(function (err, result) {
addBookArray(result);
});
}
for(var usernames in name) {
getDataByUsername(name[usernames]);
}
console.log(books);
res.send(books);
});
}

Answer 1

You're right, the problem is that Find is asynchronous and you send your response before you receive the result.
To deal with this kind of issues, you have several choices:
The powerful package Async to organize your async loops
The aggregation of MongoDB to let your DB join your data

Answer 2

Node Js is asynchronous . Your code is never wait for your query result.
Following are some options you can try :
use Async npm package
use Promise
Promise example :-
Promise.all([qry1, qry2]).then(res=>{ console.log(res) }).catch(err=>{console.log(err);})
here qry1 and qry2 are your mongo query

Answer 3

If you don't want to work with the async package, you can try to work with the $in functionality of mongoose and mongodb. As in, you get the list of users, and then find the list of books whoose userid is inside the user list.
Something along the line of :
exports.timeline = function(req, res) {
var Followers = mongoose.model('Follow');
Followers.find({'follower': req.user.username}, function(err, followerResult) {
var name = [req.user.username];
var books = [];
function addName(username) {
name.push(username);
}
for(var user in followerResult) {
addName(followerResult[user]['followed']);
}
Books.find({"username" : { $in: name }}).exec(function (err, books) {
console.log(books);
res.send(books);
});
});
}
Hope this helps.