I am new to backend and mongodb. I don't know how to close mongodb . Please help with that. Thanks in advance.

index.js

const server = require("./server");

const port = process.env.PORT || 5100;
process.on("exit", function () {
  console.log("db disconnected");
  mongoose.disconnect();
});
server
  .create()
  .then((app) => {
    app.listen(port, () => {
      console.log(`Server has started on port ${port}!`);
    });
  })
  .catch((err) => console.log(err));

server.js

const express = require("express");
const mongoose = require("mongoose");
const cors = require("cors");
require("dotenv").config();

const create = async () => {
  const app = express();
  //DB connection
  mongoose
    .connect(process.env.DB_STRING, {
      useNewUrlParser: true,
      useUnifiedTopology: true,
    })
    .then(() => console.log("MongoDB Connected"))
    .catch((err) => console.log(err));

  //Allowing cors
  app.use(cors());
  //Body parser
  app.use(express.json());

  //Middleware configuration

  //   app.use("/api/test", require("./routes/testingroute"));
  app.get("/", (req, res) => res.send("Hello World!"));

  app.use("/api/user", require("./routes/userRoute"));

  return app;
};

module.exports = {
  create,
};

this is what i have tried till now.i can able to access my db but i am not sure about the closing db properly.