connecting MySQL in express nodejs

app.js

const express = require('express');
const app = express();

/* requiring middleware */
const { getConnection } = require('./app/middlewares/mysql');

/* connecting mysql before going to requested route */
app.use('/auth', getConnection, require('./app/controllers/auth'));

config.js

/* this is config file for our application */

/* rather you can config details in process envs */

module.exports = {
    mysql : {
        host: 'localhost',
        user : 'root',
        password: '',
        database : 'mysql_database',
        connectionLimit: 10

    }
}

mysql.js

/* this file helps to connect mysql database */

/* this file location might look like this ----> /middlewares/mysql.js */

const mysql = require('mysql');
const config = require('../utils/config');

let pool;


const passConneciton = (req, res, next) => {
  pool.getConnection((err, connection) => {
    if (err) {
      next(err);
    } else {
      /* adding connection to res object, so it can be used in router */
      res.locals.mysqlConn = connection;
      next();
      /* release connection when you are done */
      res.on('finish', () => {
        connection.release();
      });
    }
  });
};


module.exports = {
  getConnection: async (req, res, next) => {
    /* if pool already been set then re-use it */
    if (pool) {
      passConneciton(req, res, next);
    } else {
      /* create pool
            here, we are getting mysql config from config.js,
            but you can also opt for process evn's
            */
      pool = mysql.createPool(config.mysql);
      passConneciton(req, res, next);
    }
  },
};