callback_avoid_2.js

const mysql = require('mysql');

// standart example from mysql documentation
(function test1() {
  const pool = mysql.createPool({
    host: '127.0.0.1',
    user: 'root',
    password: '1234',
    database: 'test',
  });
  pool.query('select * from person', (error, results, fields) => {
    if (error) throw error;
    console.log('The solution is: ', results); // query results available only here, inside callback
  });
}());

// using new Promise
function modifiedQueryFunction(pool, query) {
  return new Promise((resolve, reject) => {
    pool.query(query, (error, results, fields) => {
      if (error) {
        reject(error);
      }
      resolve(results);
    });
  });
}

(async function test2() {
  let pool;
  try {
    pool = mysql.createPool({
      host: '127.0.0.1',
      user: 'root',
      password: '1234',
      database: 'test',
    });
    const query = 'select * from person';
    const result = await modifiedQueryFunction(pool, query);
    console.log(result); // query result available here, outside of the callback
    // ... do whatever you need, without possibility for callabck hell
  } catch (e) {
    console.log(e);
  } finally {
    pool.end();
  }
}());