How to do multiple mysql querys in a single function

See more:

Windows

Hi,
i'm just starting some nodejs mysql programming right now and yet hitting my first issues. I liked my program to check before inserting whether username and email is already in use and if skip inserting. For that i thought i could simply write two queries after another. My "return ..." in all queries always run into an error. "header to a closed client" something like that. So played around to solve it.
For my understanding javascript has it's eventloop where all lets say function are somehow registered and invoked successively. So my called function "authentication" is on the loop first this function was some queries which "db.connect, db.query, db.query and db.query" placed after. So my eventloop looks like that

authentication
db.connect
db.query
db.query
db.query

So authentication ends and then db.connect starts working???
I'm usually programming in c/c++ so it's new for me.

The console output
[nodemon] starting `node app.js`
Server started on Port 5000
Server started on Port 5000
[Object: null prototype] {
name: 'Huhu',
email: 'abc@xyz.com',
password: '1',
passwordConfirm: '1'
}
After Queries: 0
MYSQL connected in authentication
email in use
name in use
[
'Huhu',
'$2b$10$Izhe85NxinEEY0IXjUJQbu6dJto0l0AkWdBuG/t1bzITGMVcosaam',
'abc@xyz.com'
]
Got new user registered

Thanks all for answering

What I have tried:

import mysql from 'mysql';
import dotenv from 'dotenv';
import jwt from 'jsonwebtoken';
import bcrypt from 'bcrypt';
import cookie from 'cookie-parser';
import util from 'util';

const sql = "INSERT INTO users (`username`, `password`, `email`) VALUES (?)";

dotenv.config({
    path: './.env'
});

function seachforEmail(db,email) {

    return new Promise((resolve,reject) => {
        db.query('SELECT email FROM users WHERE email = ?', [email], ( error, results ) => {
            if(error)
                reject(error);

            if(results.length > 0) {
                resolve(email);
            } 
            else {
                resolve(null);           
            }
        });        
    });
}

function seachforName(db,name) {

    return new Promise((resolve,reject) => {    
        db.query('SELECT username FROM users WHERE username = ?', [name], ( error, results ) => {
            if(error)
                reject(error);

            if(results.length > 0) {
                resolve(name);
            } 
            else {
                resolve(null);           
            }
        });       
    });
}

async function authentication(req,res) {
    console.log(req.body);

    if (req.body.password === req.body.passwordConfirm) {
        const salt = 10;
        var error_messages = [];
        const promises = [];
        const { name, email, password, passwordConfirm } = req.body;

        const db = mysql.createConnection({
            host: process.env.DATABASE_HOST,
            password: process.env.DATABASE_PASSWORD,
            user: process.env.DATABASE_USER,
            database: process.env.DATABASE
        });
        
        db.connect( async (error) => {
            if(error) {
                console.log(error);  
                return res.render('register', {message: 'connection failed'});              
            }
            else {
                console.log("MYSQL connected in authentication");    
                

                const db_email = await seachforEmail(db,email);
                console.log(db_email);
                if(db_email === email) {
                    console.log("Email in use");
                    return res.render('register', {message: 'Email in use'});    
                }
                else{
                    console.log("Email OK");                    
                }

                const db_name = await seachforName(db,name);
                console.log(db_name);
                if(db_name === name) {
                    console.log("Name in use");
                    return res.render('register', {message: 'Name in use'});    
                }
                else{
                    console.log("Name OK");                    
                }
                  
                bcrypt.hash(password.toString(), salt, (err, hash) => {
                    if(err)
                        return res.render('register', {message: 'Error for hashing password'});
                    
                    const values = [
                        name,
                        hash,
                        email
                    ];
            
                    console.log(values);  
                    
                    db.query('INSERT INTO users (`username`, `password`, `email`) VALUES (?)', [values], (err,data) => {
            
                        if(err) {
                            console.log("Register in failed");            
                            return res.render('register', {message: 'Inserting data failed'});        
                        }
                          
                        console.log("Got new user registered");

                        db.end();    
                        return res.render('register', {message: 'Inserting Success'});  
                    }) 

                })
            }
        })


    }
    else {
        return res.render('register', { message: 'Passwords not match' });
    }
}

export default authentication;