How to get, use, and close a DB connection using the Async module

## db-config.js
module.exports = {
  user: 'hr',
  password: 'oracle',
  connectString: 'localhost:1521/orcl',
  poolMax: 20,
  poolMin: 20,
  poolIncrement: 0
};

## employees.js
const oracledb = require('oracledb');
const async = require('async');

function getEmployee(empId, getEmployeeCallback) {
  async.waterfall(
    [
      function(callback) {
        oracledb.getConnection(function(err, conn) {
          if (err) {
            console.log('Error getting connection', err);
          } else {
            console.log('Connected to database');
          }

          callback(err, conn);
        });
      },
      function(conn, callback) {
        conn.execute(
          `select *
          from employees
          where employee_id = :emp_id`,
          [empId],
          {
            outFormat: oracledb.OBJECT
          },
          function(err, result) {
            if (err) {
              console.log('Error executing query', err);
            } else {
              console.log('Query executed');
            }

            callback(err, conn, result);
          }
        );
      }
    ],
    function(err, conn, result) {
      if (err) {
        getEmployeeCallback(err);
      } else {
        getEmployeeCallback(null, result.rows[0]);
      }

      // If error getting conn, no need to close.
      if (conn) {
        conn.close(function(err) {
          if (err) {
            console.log('Error closing connection', err);
          } else {
            console.log('Connection closed');
          }
        });
      }
    }
  );
}

module.exports.getEmployee = getEmployee;

## index.js
const oracledb = require('oracledb');
const async = require('async');
const dbConfig = require('./db-config.js');
const employees = require('./employees.js');

async.series(
  [
    function(callback) {
      oracledb.createPool(dbConfig, function(err) {
        callback(err);
      });
    },
    function(callback) {
      employees.getEmployee(101, function(err, emp) {
        if (err) {
          callback(err);
          return;
        }

        console.log(emp);
      });
    }
  ],
  function(err) {
    if (err) {
      console.log(err);
    }
  }
);

## package.json
{
  "name": "async-module",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "Dan McGhan <dan.mcghan@oracle.com> (https://jsao.io/)",
  "license": "ISC",
  "dependencies": {
    "async": "^2.4.1",
    "oracledb": "^1.13.1"
  }
}