Send a JSON array as response from Node.js

Question

I am fetching data from a MongoDB database then putting it in a cursor to send that as a Node.js response.

var router = express.Router();
var MongoClient = require('mongodb').MongoClient;
var url = 'mongodb://localhost/EmployeeDB';
/* GET users listing. */
router.get('/', function(req, res, next) {
  //res.send('respond with a resource');
  MongoClient.connect(url, function(err, db) {
    var cursor = db.collection('Employee').find();
    cursor.each(function(err, doc) {

      console.log(doc);
      arrayres = doc ;
     res.send(doc);

    });
    db.close();
  });
});

module.exports = router;

It sends only the first record then I get this error:

Error [ERR_HTTP_HEADERS_SENT]: Cannot remove headers after they are sent to the client
    at ServerResponse.removeHeader (_http_outgoing.js:528:11)
    at ServerResponse.send

Notice: I get this error only when there are multiple records to send as response.

You can only send back one response to the browser (be it res.send(), res.end(), res.sendFile(), res.json() or any other). You can't have that inside a .forEach(). — Jeremy Thille
– Jeremy Thille, Commented Feb 28, 2020 at 14:34
With Mongoose, you'd be like Model.find().lean().exec( docs => res.json(docs)) — Jeremy Thille
– Jeremy Thille, Commented Feb 28, 2020 at 14:38

Abel Vinuela · Accepted Answer · 2020-02-28 15:17:16Z

1

You are sending the response twice. Which is impossible ( look at Why can't we do multiple response.send in Express.js? )

  res.send('respond with a resource');

Here and

res.send(arrayres);

Here.

Here is a working example based on jeremy's answer :

router.get('/', function (req, res, next) {
    MongoClient.connect(url, function (err, db) {
        var cursor = db.collection('Employee').find();

        let employees = []
        const pushData = async () => {
            cursor.forEeach( function (doc) {
                employees.push(doc);
            });
        }
        const sendResponse = async () => {
            await pushData();
            res.json(employees);
        }
    });
});

edited Feb 28, 2020 at 15:17

answered Feb 28, 2020 at 14:27

Abel Vinuela

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3 Comments

CoderTn Over a year ago

still having the same error even after sending a single response , please watch the post content update , thanks .

Abel Vinuela Over a year ago

This is still the same issue, you are sending a response for each employee you have. You must send one and only one response.

Abel Vinuela Over a year ago

Look at the edit i made. I hope it will work for you

Jeremy Thille · Accepted Answer · 2020-02-28 14:51:08Z

0

You can only send back one response to the browser (be it res.send(), res.end(), res.sendFile(), res.json() or any other). So, you can't have that inside a .forEach().

First, build an array, then send your data back once.

router.get('/', function (req, res, next) {
    MongoClient.connect(url, function (err, db) {
        var cursor = db.collection('Employee').find();

        let employees = []

        cursor.forEeach( function (doc) {
            employees.push(doc);
        });

        res.json(employees);
    });
});

Or with Mongoose :

Employee.find().lean().exec( (err,docs) => res.json(docs))

edited Feb 28, 2020 at 14:51

answered Feb 28, 2020 at 14:42

Jeremy Thille

26.4k12 gold badges48 silver badges64 bronze badges

4 Comments

CoderTn Over a year ago

thank you @jeremy Thille for your answer but i actually sending an empty array "[ ]" i think there is a problem with push into the array

Jeremy Thille Over a year ago

Yes, it should be cursor.forEeach( function (doc). Fixed

CoderTn Over a year ago

still having the same issue ! empty array sent to the browser .

Jeremy Thille Over a year ago

Well that's a different problem. How to build the data you send back is something else. I don't use Mongo's native driver, so I don't know how to use cursor. Mongoose makes your life so much easier :) Anyway you get the idea, you can't use res.end() more than once.

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