Mongo Connection Sharing

index.js

Promise.resolve()
    .then(() => require("./lib/mongoUtil").connect()) // Here you could pass in { host: "something", port: "something", dbname: "something" } to connect
    .then(() => require("./lib/server"))
    .catch(err => {
        console.error("Error:", err);
        process.exit();
    });

MongoUtils.js

var _db;

module.exports = {
    connect: function ({host = "localhost", port = 27017, dbname = "exampleDb"} = {}) {
        return require("mongodb").MongoClient.connect(`mongodb://${host}:${port}/${dbname}`)
            .then(db => _db = db);
    },
    collection: function (col_name) {
        if ( !_db ) {
            return null;
        }
        return _db.collection(col_name);
    },
    get db() { return _db; }
};

someRoute.js

const Video = require("../lib/mongoUtil").collection("Video");

/* or for multiple */

const db = require("../lib/mongoUtil").db;

const Video = db.collection("Video");
const User = db.collection("User");