connect () {
  this.connection = mysql.createConnection({
    host: process.env.DB_HOST,
    user: process.env.DB_USER,
    password: process.env.DB_PASSWORD,
    database: process.env.DB_DATABASE
  }, function (error, lofasz) {
    // this === undefined

    this.connection.connect();
  });
}

connect () {
  this.connection = mysql.createConnection({
    host: process.env.DB_HOST,
    user: process.env.DB_USER,
    password: process.env.DB_PASSWORD,
    database: process.env.DB_DATABASE
  }, (error, lofasz) => {
    // this === fasza

    this.connection.connect();
  });
}