How to reuse MongoDB connection for multiple API routes?

[SergiiMost]

While using Express, one of the easy ways to reuse a MongoDB connection was to open a new connection when the Node.js application starts and attach it to app.locals . Something like this:
/server.js

import express from 'express';
import logger from 'winston';
import { MongoClient } from 'mongodb';
import config from './config';

const app = express();

app.get('/', (req, res) => {
  res.send('Hello World');
});

// Create a MongoDB connection pool and start the application
// after the database connection is ready
MongoClient.connect(config.database.url, (err, db) => {
  if (err) {
    logger.warn(`Failed to connect to the database. ${err.stack}`);
  }
  app.locals.db = db;
  app.listen(config.port, () => {
    logger.info(`Node.js app is listening at http://localhost:${config.port}`);
  });
});

And then I can reuse this DB connection wherever i need :
const db = req.app.locals.db

So, how do I do it in Next.js without Express server? I don't think it's a good idea to just open MongoDB connections in every API route. There should be a good way to cache that connection and reuse it between API routes. I couldn't find a good explanation regarding my question. I would appreciate any help or clarification. Thank you!