Exporting a function declared inside asynchronous function - node.js

Question

I have a file in which mongoose is setup
const keys = require('../chat/config/keys');
const mongoose = require('mongoose');
const dbURI = keys.mongoURI;
mongoose.connect(dbURI, { useNewUrlParser: true });
mongoose.set('debug', true);
let fetchVideo;
mongoose.connection.once('open', function () {
console.log('Mongoose default connection open to ' + dbURI);
let connectToDB = mongoose.connection.db;
let videoChatDB = connectToDB.collection('videochat');
fetchVideo = ({ id }) => {
if (id !== '100') {
videoChatDB.findOne({'studentID': parseInt(id)}).then((user) => {
if (user) {
console.log(user);
return true;
} else {
console.log(user);
return false;
}
});
}
}
});
module.exports = { fetchVideo };
And I am requiring that file inside my index.js file like so:
let db = require('./db');
In my index file I have a socket connection and I need to check the database when a new user comes.
socket.on('new-user', async (user) => {
let checkAvail = await db.fetchVideo(user);
});
But I am getting this error:
TypeError: db.fetchVideo is not a function
I am guessing it is undefined since it is declared inside an asynchronous function.
How would I make this to work?

Answer 1

Because the function is created asynchronously, one option is to export a Promise that resolves to fetchVideo function. Because mongoose.connection.once is callback-based, you'll have to transform it into a Promise.
If you want fetchVideo to resolve to something (rather than nothing), you also have to properly chain the findOne call with the promise chain; to fix that, return videoChatDB.findOne....
const fetchVideoProm = new Promise((res, rej) => {
mongoose.connection.once('open', function () {
console.log('Mongoose default connection open to ' + dbURI);
let connectToDB = mongoose.connection.db;
let videoChatDB = connectToDB.collection('videochat');
const fetchVideo = ({ id }) => {
if (id !== '100') {
return videoChatDB.findOne({'studentID': parseInt(id)}).then((user) => {
if (user) {
console.log(user);
return true;
} else {
console.log(user);
return false;
}
});
}
}
res(fetchVideo);
});
});
module.exports = { fetchVideoProm };
Consume it by awaiting the creation of the fetchVideo function, and then calling it:
socket.on('new-user', async (user) => {
const fetchVideo = await db.fetchVideoProm;
const checkAvail = await fetchVideo(user);
});