NodeJS/MongoDB - Error: Can't set headers after they are sent

Question

I got this helper function:

const Account = require('../models/account');

exports.sendInvites = (accountIds, invite, callback) => {

  if (!accountIds) {

    callback('No account ids provided', null, null);

    return;
  }

  accountIds.forEach((id) => {
    Account.findOneAndUpdate({_id: id}, {$push: {organisationInvites: invite}}, callback);
  });
};

Then I have this route:

router.post('/organisations', auth.verifyToken, (req, res, next) => {

  const organisation = new Organisation({
    name: req.body.name,
    email: req.body.email,
    admins: [req.body.createdBy],
    createdBy: req.body.createdBy
  });

  organisation.save((err, organisation) => {

    if (err) {

      return res.status(500).json({
        error: err,
        data: null
      });
    }

    organisationUtils.sendInvites(req.body.invites, {
      inviter: req.body.createdBy,
      organisation: organisation._id
    }, (err, account, response) => {

      if (err) {

        return res.status(500).json({
          error: err,
          data: null
        });
      }

      res.json({
        error: null,
        data: organisation
      });
    });
  });
});

I get a Error: Can't set headers after they are sent. error for the

res.json({
  error: null,
  data: organisation
});

part but I can't understand why this is happening. I tried looking at the accepted answer here Error: Can't set headers after they are sent to the client, did some digging but couldn't find any specific reason still what's happening in my particular example above. Any ideas?

You could not use callback in a loop.Callback must be called after all the db operations has been completed. — Atul Agrawal, Nov 16 '17 at 14:24
Use async library if you really wants to use callback multiple times. ```https://caolan.github.io/async/docs.html``` — Atul Agrawal, Nov 16 '17 at 14:25

score 2 · Accepted Answer · answered Nov 16 '17 at 13:16

You are calling the callback multiple times, and so res.json multiple times. Gather the data from all database request then perform an unique res.json.

accountIds.forEach((id) => {
    Account.findOneAndUpdate(
                              {_id: id}, 
                              {$push: {organisationInvites: invite}},
                               callback,
                            );
});

Something like :

    var allData = [];
    var nbRequestDone = 0;

    var waitAllCallback = function (data, err) {
       if (err) {
         callback(err);

         nbRequestDone = accountIds.length;

         return;
       }

       nbRequestDone += 1;

       allData.push(data);

       if (nbRequestDone === accountIds.length) {
         callback(false, allData);
       }
    };

    accountIds.forEach((id) => {
      Account.findOneAndUpdate(..., waitAllCallback);
    });

So I tried it and it works, however sometimes the request doesn't return a response to the client side. Any idea why that could be? — Chrillewoodz, Nov 16 '17 at 14:40
Did you checked if the error got returned? (first parameter) — Orelsanpls, Nov 16 '17 at 14:43
I think I resolved it. There was a condition check which failed half of the times, reason unknown. Thanks. — Chrillewoodz, Nov 16 '17 at 15:15

score 0 · Answer 2 · answered Mar 28 '19 at 07:15

0

this video covers the Error regarding "Error: Can't set headers after they are sent". https://www.youtube.com/watch?v=rKTlakY8j2M

In summary of the video, this error shows up when you have an extra callback in your code. Hope this helps. Been struggling with this one too for quite some time.

answered Mar 28 '19 at 07:15

John Myrrh

1
1

2

While this link may answer the question, it is better to include the [essential parts of the answer](https://meta.stackexchange.com/a/8259) here and provide the link for reference. Link-only answers can become invalid if the linked page changes. – adiga Mar 28 '19 at 07:22

NodeJS/MongoDB - Error: Can't set headers after they are sent

2 Answers2