how to export array created in a promise - node.js

Question

I'm trying to follow a project from mozilla developer local library tutorial
. It includes learning how to use nodejs, express, mongoose and mongoDB. I am swapping out mongoose and mongoDB with firestore and using firebase functions to eventually host with firebase hosting.
The project uses a model, view, controller structure. I really want to stick to this structure to help break everything down into manageable chunks.
The first problem I’m trying to resolve is to return an array that I created in a promise to be exported as a function that is called from booksController.js.
A concise view of the structure I have is:
index.js
const booksRouter = require('./routes/books');
app.use('/books', booksRouter);
routes/books.js
const books_controller = require('../controllers/booksController');
router.get('/', books_controller.index);
controllers/booksController.js
var Books = require('..models/books');
exports.index = function(req, res){
var books = Books.AllBooks();
res.render('books',{books: books});
};
models/books.js
var booksRef = db.collection(books);
var allBooks = booksRef.get()
.then(snapshot => {
var books = [];
Snapshot.forEach(doc => {
books.push({doc.data: doc.data()});
});
});
.catch(err =>{
console.log('Error getting documents', err);
});
exports.AllBooks = function(req, res){
return books;
}
I've tried wrapping the promise in a function and returning the array to export it but I get undefined when console logging in booksController.js.
Can someone please enlighten me and complete the puzzle of how to return the array so it can be exported.

Answer 1

What you're trying to do, can't be done using require, since require is synchronous.
Instead what you can do is export a function that will fetch the books asynchronously, and use that function in your controller.
models/books.js
const booksRef = db.collection(books);
async function getBooks() {
// You can implement a cache and fetch the books only once.
const snapshot = await booksRef.get()
const books = [];
snapshot.forEach(doc => {
books.push({
doc.data: doc.data()
});
});
return books;
}
module.exports = getBooks;
controllers/booksController.js
const getBooks = require('./../models/books');
exports.index = async function(req, res){
const books = await getBooks(); // Handle exception
res.render('books',{books: books});
};