db.js

'use strict';
const MongoClient = require('mongodb').MongoClient;
const config = require('./config');

const state = {
  db: null,
};

exports.connect = function (url, done) {
  if (state.db) { return done(); }

  MongoClient.connect(url, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
  }, function (err, client) {
    const db = client.db(config.DATABASE);
    if (err) { return done(err); }
    state.db = db;
    done();
  });
};

exports.get = function () {
  return state.db;
};

exports.close = function (done) {
  if (state.db) {
    state.db.close(function (err, result) {
      state.db = null;
      state.mode = null;
      done(err);
    });
  }
};