Node js Mongo DB Connection Code Snippet (https://nodejstutorials.net/creating-a-crud-rest-api-service-with-nodejs-express-and-mongodb)

mongoConfig.js

const mongoose = require("mongoose");
const DB_URL = process.env.MONGO_URI;
module.exports = () => {
  const connect = () => {
    mongoose.Promise = global.Promise;

    mongoose.connect(
      DB_URL,
      {
        keepAlive: true,
        useNewUrlParser: true,
        useUnifiedTopology: true,
      },
      (err) => {
        let dbStatus = "";
        if (err) {
          dbStatus = `*    Error connecting to DB: ${err}\n****************************\n`;
        }
        dbStatus = `*    DB Connection: OK\n****************************\n`;
        if (process.env.NODE_ENV !== "test") {
          // Prints initialization
          console.log("****************************");
          console.log("*    Starting Server");
          console.log(`*    Port: ${process.env.PORT || 3000}`);
          console.log(`*    NODE_ENV: ${process.env.NODE_ENV}`);
          console.log(`*    Database: MongoDB`);
          console.log(dbStatus);
        }
      }
    );
    mongoose.set("useCreateIndex", true);
    mongoose.set("useFindAndModify", false);
  };
  connect();
  mongoose.connection.on("error", console.log);
  mongoose.connection.on("disconnected", connect);
//loadModels
};

Refer Here