Node js I can't return a query using mysql

Question

When I try to return a query, we get an undefined object, I don't know why, I need to return a value to the main function but always is undefined, I need to return that information to validate a user in the database, when I do the same function in main was working, but when I try to separate the functions can't work.

class login{

    validateUser(user, pass){
        const connection = require ('./db');
        let datos = connection.query('SELECT * FROM login WHERE usuario = ?', [user], async(error, results)=>{
            if (results.length == 0 || pass != results[0].password){
                return null;
            }
            else{
                return results;
            }
        });
    }
}

module.exports = login

I need to return values in this function to validate login:

app.post('/auth', async (req, res)=>{
    const user = req.body.user;
    const pass = req.body.pass;

    
    const log = new login();

    const response = log.validateUser(user, pass);
    console.log(response);
    

    if(!response){
        res.render('login',{
            alert:true,
            alertTitle: "Error",
            alertMessage: "Usuario y/o Contraseña incorrecta",
            alertIcon : "error",
            showConfirmButton: true,
            timer: null,
            ruta: 'login'
        });
    }
    else{
        req.session.loggedin=true;
        req.session.name = response[0].usuario;
        res.render('login',{
            alert:true,
            alertTitle: "Conexión exitosa",
            alertMessage: "!Login exitoso¡",
            alertIcon : "success",
            showConfirmButton: false,
            timer: 2000,
            ruta: ''
        });
    }
});

Answer 1

I think the problem is in these lines

1. const response = log.validateUser(user, pass);
2. console.log(response);

This code is running Asynchronously so line 2 is running before the completion of line 1 that is why you are getting the response as undefined.

I suggest you use Async await for this if your database client supports it or make your custom Promise such that you code do

//note the await keyword before log
1. const response = await log.validateUser(user, pass);
2. console.log(response);

This will make sure that line 2 or any code below only executes once you have fetched and returned your data properly

P.S: Above fix won't work until unless your fix the implementation of validateUser to support Async Await via Promise