async await is not in hold state mongoose

Question

I don't know why first it prints data return instead of after loop done

code

exports.put = async function (req, res, next) {
    const data = Array.from(req.body);
    let errors = false;
    data.forEach(async (update, index) => {
        try {
            const result = await TypeofAccount.findByIdAndUpdate(
                new mongoose.Types.ObjectId(update._id),
                {
                    $set: { name: update.name },
                },
                { new: true, runValidators: true },
            );
            console.log(index);
            if (!result) {
                errors = true;
                console.log('errors');
                return res.status(500).send();
            }
        } catch (e) {
            return res.status(500).send();
        }
    });
    console.log('data return');
    res.json(data);
};

data return
PUT /api//typeofaccount 200 5.551 ms - 202
0
1
2

Marking the callback function passed to `forEach()` as `async` only makes that callback return a promise, it doesn't make `forEach()` run asynchronously. — Lennholm, Jul 01 '20 at 09:25
Thank you @BilalAkbar, it is working fine with for of, strange behavior of javascript, i have been thinking it should run after forEach — Indraraj26, Jul 01 '20 at 09:34
It's perfectly logical behavior once you understand how `async-await` actually works. Keep in mind that unlike `for-of`, `forEach()` isn't a language feature, it's part of the array API. — Lennholm, Jul 01 '20 at 09:45

Atharva Deshpande · Answer 1 · 2020-07-01T10:29:23.280

0

The .for each function runs asynchronously and that is why you can see the console.log which is after the loop get printed first

edited Jul 01 '20 at 10:29

answered Jul 01 '20 at 09:27

Atharva Deshpande

31
4

"*runs on another thread*" - no, definitely not. – Bergi Jul 01 '20 at 09:44
I am sorry I didn't put it correctly but I meant that it runs asynchronously and that's why the code below it prints first – Atharva Deshpande Jul 01 '20 at 09:52
Please [edit] your answer to fix the wording then – Bergi Jul 01 '20 at 09:54

score 0 · Answer 2 · answered Jul 01 '20 at 09:38

this problem happened becouse you are use forEach loop , asyc await not working with forEach , to avoid this problem your code block should be like

for(let i in data){
try {
            const result = await TypeofAccount.findByIdAndUpdate(
                new mongoose.Types.ObjectId(data[i]._id),
                {
                    $set: { name: data[i].name },
                },
                { new: true, runValidators: true },
            );
            console.log(i);
            if (!result) {
                errors = true;
                console.log('errors');
                return res.status(500).send();
            }
        } catch (e) {
            return res.status(500).send();
        }
}

async await is not in hold state mongoose

2 Answers2