Node mysql auto connect and close

app.js

var mysql = require('mysql');

var db_config = {
host     : 'localhost',
user     : 'usuario',
password : 'password',
database : 'ddbb'
};

var connection = {};
connection.query = function (sql, callback) {
  var _err;
  var _rows;
  var conn = mysql.createConnection(db_config);
  conn.query(sql, function (err, rows) {
    _err = err;
    _rows = rows;
  });
  conn.end(function () {
    callback(_err, _rows);
  });
};


connection.query('SELECT 1 + 1 AS solution', function (error, results, fields) {
  if (error) throw error;
  console.log('The solution is: ', results[0].solution);
});