db.js

import mysql from 'mysql';

export default class Db 
{
  this.conn = false;
  
  connect()
  {
    // fixme: db settings are hardcoded
    // fixme: no error handling here
    // fixme: no async here
    this.conn = mysql.createConnection({
      host     : 'localhost',
      user     : 'me',
      password : 'secret',
      database : 'my_db'
    });
    
    this.conn.connect();
  }

  close()
  {
    if(this.conn)
      this.conn.end();
  }
  
  async query(sql, args)
  {
    if(!this.conn)
      throw 'DB not connected';
    
    return await new Promise((ok, fail) =>
      this.conn.query(sql, args, (err, rows, fields) => 
        err ? fail(err) : ok(fields)
      );
    );
  }
  
  async queryStream(sql, args, cb)
  {
    if(!this.conn)
      throw 'DB not connected';
    
    return await new Promise((ok, fail) => {
      var q = this.conn.query(sql, args);
      q.on('error', err => fail(err));
      q.on('end', () => ok());
      q.on('result', row => { 
        cb(row); q.resume();
      });
    }
  }
}