web browser crashes when using mysql prepared query with nodejs - mysql

Question

I want to return the result of query to DB, which I think would be a promise and then consume that promise in another file.Here is my model code (User.js) :
User.prototype.login = function () {
return new Promise((resolve, reject) => {
pool.execute('SELECT * FROM `users` WHERE `username` = ? AND `password` = ?', [this.data.username, this.data.password], (err, attemptedUser) => {
if (err) {
pool.release();
return reject(err);
} else {
pool.release();
return resolve(attemptedUser);
}
});
});
}
and the code in my controller file (userController.js):
const User = require('../models/User');
exports.login = (req, res) => {
let user = new User(req.body);
user.login()
.then((result) => {
res.send(result);
})
.catch((err) => {
res.send(err);
});
};
But when I click on the login button the page doesn't go to the specified URL and keeps working until crash.
Where is the problem?
UPDATE-1
This is my db.js :
const mysql = require('mysql2/promise');
const dotenv = require('dotenv');
dotenv.config();
const pool = mysql.createPool({
host: process.env.DB_HOST,
user: process.env.DB_USERNAME,
password: process.env.DB_PASSWORD,
database: process.env.DB_NAME,
connectionLimit: 100
});
module.exports = pool;