Returned array has undefined value - node.js

Question

I am trying to return an array through async/await:
app.get('/users/article/feed',checkAuthenticated,async (request,response)=>{
try{
function executor(){
let articleArray=[]
const sql="SELECT noOfArticles FROM Articles WHERE id=?"
db.query(sql,[request.user.id], (err,result)=>{
if(err) throw err
let noOfArticles=result[0].noOfArticles
for(let i=1;i<=noOfArticles;i++){
const sql1="SELECT ?? FROM Articles WHERE id=?"
let index='article'+i
db.query(sql1,[index,request.user.id],(err,result)=>{
if(err) throw err
articleArray.push(result[0][index])
if(articleArray.length===noOfArticles){
console.log(articleArray); //here the array is printed as expected
return articleArray;
}
})
}
})
}
const resultArray= await executor();
console.log(resultArray); //here the array is undefined
response.render('viewArticles');
} catch(e){
console.log(e);
}
})
The resultArray is always undefined.
I know this is a very old question. I tried checking all the other answers in Stack Overflow but I am confused a lot about this. I am a newbie to js so I couldn't understand it properly. How can I solve this?

Answer 1

You are returning from inside the callback function, which won't work since executor doesn't wait for your queries responses. Return a Promise instead.
function executor() {
return new Promise((resolve,reject) => {
let articleArray = [];
const sql = "SELECT noOfArticles FROM Articles WHERE id=?";
db.query(sql, [request.user.id], (err, result) => {
if (err) return reject(err);
let noOfArticles = result[0].noOfArticles;
for (let i = 1; i <= noOfArticles; i++) {
const sql1 = "SELECT ?? FROM Articles WHERE id=?";
let index = "article" + i;
db.query(sql1, [index, request.user.id], (err, result) => {
if (err) return reject(err);
articleArray.push(result[0][index]);
if (articleArray.length === noOfArticles) {
console.log(articleArray); //here the array is printed as expected
return resolve(articleArray);
}
});
}
});
})
}

Answer 2

Does it return some result if you make the function you are calling async?
async function executor(){
let articleArray=[]
const sql="SELECT noOfArticles FROM Articles WHERE id=?"
db.query(sql,[request.user.id], (err,result)=>{
if(err) throw err
let noOfArticles=result[0].noOfArticles
for(let i=1;i<=noOfArticles;i++){
const sql1="SELECT ?? FROM Articles WHERE id=?"
let index='article'+i
db.query(sql1,[index,request.user.id],(err,result)=>{
if(err) throw err
articleArray.push(result[0][index])
if(articleArray.length===noOfArticles){
console.log(articleArray); //here the array is printed as expected
return articleArray;
}
})
}
})
}

Answer 3

When you return articleArray, you are not returning it from the executor function. Instead you are returning it from the callback that is passed into the db.query function. The () => {} syntax is basically shorthand for function() {} (although there are differences that are outside the scope of this answer).
Perhaps something like this might be helpful (note that I removed the try catch, as I believe such logging should be done at the middleware level in express, which it seems you are using):
app.get('/users/article/feed', checkAuthenticated, async (request, response) => {
return new Promise((resolve, reject) => {
let articleArray = []
const sql = "SELECT noOfArticles FROM Articles WHERE id=?"
db.query(sql, [request.user.id], (err, result) => {
if (err) reject(err)
let noOfArticles = result[0].noOfArticles
for (let i = 1; i <= noOfArticles; i++) {
const sql1 = "SELECT ?? FROM Articles WHERE id=?"
let index = 'article' + i
db.query(sql1, [index, request.user.id], (err, result) => {
if (err) reject(err); // reject the promise if there is an error
articleArray.push(result[0][index])
if (articleArray.length === noOfArticles) {
console.log(articleArray);
resolve(articleArray); // resolve the promise with the value we want
}
})
}
})
})
})