如何使用 SQLite3 和 node.js 从异步 function 返回值？

Question

I'm trying to make a small database using SQLite3 for my discord bot (on node.js), and I'd like to make a function that updates the database with provided values (this part works) or return a value of the database.

My problème is here, the returned value is always undefined...

I have understood that SQLite3 commands are asynchronous so all the functions become asynchronous, but how I can make sure that the returned value be no longer undefined?

Here is my code:

const sqlite3 = require('sqlite3');
const dbname = 'dbStocks';

module.exports = function gestionBDD(update, nomArticle, quantitéArticle) {
 console.log('1 ' + quantitéArticle);

 let db = new sqlite3.Database(dbname, (err) => {
  if (err) throw err;
  console.log('Démarrage de ' + dbname);
 });

 db.serialize(() => {
  nomArticle = '"' + nomArticle + '"';

  if (update) {
   //Si update est true : maj des quantités via le tableau articles

   db.run(
    `UPDATE stocks
                SET Quantité = (` +
     quantitéArticle +
     `)
                WHERE Article = (` +
     nomArticle +
     `)`
   );
  } else if (!update) {
   db.each(
    `SELECT Quantité FROM stocks WHERE Article  = (` + nomArticle + `)`,
    (err, data) => {
     console.log('2 ' + data.Quantité);
     return data.Quantité;
    }
   );
  }

  console.log('4 ' + quantitéArticle);
  db.close((err) => {
   if (err) throw err;
   console.log('Arrêt de ' + dbname);
  });
 });
};

And I get this result:

1 undefined
4 undefined
3 undefined
Démarrage de dbStocks
2 500
Arrêt de dbStocks

(the 3 undefined is a console.log() in my index.js where my function gestionBDD is call)

Answer 1

You can return a promise that can get resolved later for function return like this:

return new Promise((resolve, reject) => {
 db.run(`query statement here`, (err, row) => {
  if (err) reject(err);
  resolve(row);
 });
});

Writing this at the top of the function to make it async function. when calling the function use ether await or then to get a return result data.