Node js foreach done function - node.js

Question

Insted of using setTimeout, what should I use after foreach complete?
app.post('/grid', function(req, res){
getResults(req.body.idarray, function(callback){
res.send(callback);
});
});
function getResults(userIds, callback) {
var totalresult = [];
userIds.forEach(function (user) {
sequence
.then(function (next) {
db.query('SELECT given FROM books WHERE user_id = ?', [user.userId], function (err2, result) {
if (err2) throw err2;
next(err, result);
});
})
.then(function (next, err, books) {
db.query('SELECT received FROM encycs WHERE user_id = ?', [user.userId], function (err3, result2) {
if (err3) throw err3;
next(err, result2, books);
});
})
.then(function (next, err, books, encycs ) {
Calculation(books, encycs, function (cb) {
totalresult.push(cb);
});
next();
});
});
setTimeout(function() {
console.log(totalresult); // output ok.
return callback(totalresult); // returning as expected
}, 2000);
}
I dont know what totalresult.length is. So i can't check the length.

Answer 1

So, according to your use case you need to call callback somehow and pass totalresult into it, because that what your external code, code in the route expected.
To do that, you can call callback before calling next of the third .then statement. Like that.
...
.then(function (next, err, books, encycs ) {
Calculation(books, encycs, function (cb) {
totalresult.push(cb);
});
callback(totalresult);
next();
//console.log(totalresult); //output OK.
});
This might work.
Update 1
It is hard to follow with your code. Can't catch up the logic of it. I would propose you Promises approach. I prepared that solution, that might work. It might contain little errors, but it represents the main idea of what you are trying to achieve, and how it can be done.
app.post("/grid", (req, res) => {
getResults(req.body.idarray)
.then(data => {
res.status(200).json(data);
})
.catch(err => {
console.error("Error occured", err);
res.status(500).json(err);
});
});
function getResults(userIds) {
let promises = userIds.map(loadCalculation);
//this will wait until all loadings are done
return Promise.all(promises);
}
function loadCalculation(user) {
//parallel loading of the books and encycs
return Promise.all([loadBooks(user), loadEncycs(user)])
.then(results => {
let books = results[0];
let encycs = results[1];
let totalresult = [];
Calculation(books, encycs, function (cb) {
totalresult.push(cb);
});
return totalresult;
});
}
function loadBooks(user) {
return makeQuery('SELECT given FROM books WHERE user_id = ?', user);
}
function loadEncycs(user) {
return makeQuery('SELECT received FROM encycs WHERE user_id = ?', user);
}
function makeQuery(query, user) {
return Promise((resolve, reject) => {
db.query(query, [user.userId], function (err, result) {
if(err) {
reject(err);
} else {
resolve(result);
}
});
});
}
Please, note that this is not really performant way to load the data from database, at least, I'm sure that you there is a possibility to load all the books and encycs with a single query, because you are using SQL, and it is really flexible language.