How do I consume the JSON POST data in an Express application

Question

I'm sending the following JSON string to my server.

(
        {
        id = 1;
        name = foo;
    },
        {
        id = 2;
        name = bar;
    }
)

On the server I have this.

app.post('/', function(request, response) {

    console.log("Got response: " + response.statusCode);

    response.on('data', function(chunk) {
        queryResponse+=chunk;
        console.log('data');
    });

    response.on('end', function(){
        console.log('end');
    });
});

When I send the string, it shows that I got a 200 response, but those other two methods never run. Why is that?

score 562 · Accepted Answer · edited Dec 26 '20 at 21:55

562

I think you're conflating the use of the response object with that of the request.

The response object is for sending the HTTP response back to the calling client, whereas you are wanting to access the body of the request. See this answer which provides some guidance.

If you are using valid JSON and are POSTing it with Content-Type: application/json, then you can use the bodyParser middleware to parse the request body and place the result in request.body of your route.

For earlier versions of Express (< 4)

var express = require('express')
  , app = express.createServer();

app.use(express.bodyParser());

app.post('/', function(request, response){
  console.log(request.body);      // your JSON
  response.send(request.body);    // echo the result back
});

app.listen(3000);

Test along the lines of:

$ curl -d '{"MyKey":"My Value"}' -H "Content-Type: application/json" http://127.0.0.1:3000/
{"MyKey":"My Value"}

Updated for Express 4+

Body parser was split out into it's own npm package after v4, requires a separate install npm install body-parser

var express = require('express')
  , bodyParser = require('body-parser');

var app = express();

app.use(bodyParser.json());

app.post('/', function(request, response){
  console.log(request.body);      // your JSON
   response.send(request.body);    // echo the result back
});

app.listen(3000);

Update for Express 4.16+

Starting with release 4.16.0, a new express.json() middleware is available.

var express = require('express');

var app = express();

app.use(express.json());

app.post('/', function(request, response){
  console.log(request.body);      // your JSON
   response.send(request.body);    // echo the result back
});

app.listen(3000);

edited Dec 26 '20 at 21:55

themefield

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answered Apr 04 '12 at 08:33

Pero P.

22,259
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How would I access "MyKey" to get "My Value"? – neuromancer Apr 04 '12 at 09:07
How come it doesn't work for console.log("request = " + request.body)? – neuromancer Apr 04 '12 at 09:40
5

Because the concatenation invokes `toString()` on the object. Take a look at the node docs for `console.log`, as that inspects the object and returns a string representation. – Pero P. Apr 04 '12 at 10:15
I thought it was something like that. So how can I change it so it works? – neuromancer Apr 04 '12 at 10:26
14

`console.log('request =' + JSON.stringify(request.body))` – Pero P. Apr 04 '12 at 16:49
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/9706/discussion-between-neuromancer-and-pero-pejovic) – neuromancer Apr 04 '12 at 23:32
3

The current `console.log()` will automatically stringify an object (via `util.inspect()`), so this would work: `console.log("with request", request.body);` – Tommy Stanton Oct 01 '13 at 23:10
Hi i have the following issue: http://stackoverflow.com/questions/19917401/node-js-express-request-entity-too-large/ and the following code: http://codepen.io/mike-jam-es/pen/hHbwJ Express: 3.4.4 If someone could provide some help on this it would be very much appreciated thanks! – mike james Nov 13 '13 at 20:58
5

This answer is outdated, but the one from @chrisarton is up to date. – Emil Ingerslev Jan 11 '16 at 09:30
@pero can you please help me with this: https://github.com/expressjs/body-parser/issues/213 – codeinprogress Dec 21 '16 at 15:14
I resolved PayloadTooLargeError by `app.use(express.json({ limit: "50mb" }));` – Nikhil VJ Oct 04 '20 at 08:43
Outdated, pls look at the @chrisarton answer – Eugene Feb 08 '21 at 13:21

chrisarton · Answer 2 · 2014-07-08T15:21:28.847

218

For Express v4+

install body-parser from the npm.

$ npm install body-parser

https://www.npmjs.org/package/body-parser#installation

var express    = require('express')
var bodyParser = require('body-parser')

var app = express()

// parse application/json
app.use(bodyParser.json())

app.use(function (req, res, next) {
  console.log(req.body) // populated!
  next()
})

edited Jul 08 '14 at 15:21

answered Jul 08 '14 at 15:05

chrisarton

4,231
2
16
15

27

why do they keep taking out stuff everyone uses? – light24bulbs Oct 17 '14 at 04:30
12

@light24bulbs So it (Express) will be more lean and mean for those who don't use/need that. – andyengle Nov 04 '14 at 02:38
6

@andyengle That does make sense. But I think virtually everyone uses request parsing. That seems like a core feature to me. – light24bulbs Nov 05 '14 at 02:54
26

Since the middleware function interface is a standard used by many libraries, it also allows apps that don't use Express to use these middleware functions. – Anm Jan 31 '15 at 12:53
3

Taking it out of express doesn't allow it to be used by apps that do not use requests. They could have made it separate, and included it in express by default. – J.J Oct 23 '16 at 14:31
2

my body returns empty when data type is JSON – mrid Oct 04 '17 at 06:25
Typical engineers eh – JCraine Jul 20 '20 at 01:59

score 33 · Answer 3 · answered Jan 10 '19 at 03:10

33

For those getting an empty object in req.body

I had forgotten to set headers: {"Content-Type": "application/json"} in the request. Changing it solved the problem.

answered Jan 10 '19 at 03:10

Daniel Thompson

1,751
19
32

2

Can't believe I missed this! I was sending with `text/json` and getting `{}` as a response. Total oversight on my part. Very helpful. – James M. Lay Jan 24 '19 at 01:03
1

Ugh -- I missed this too. Thank you for posting this so I don't waste more time than I already have! – Steve Gomez Feb 06 '20 at 18:13
1

wow, thanks! life saver! easy to forget when invoking a lambda directly on the command line! `serverless invoke local -f app -l -d '{ "path": "/conferences", "httpMethod": "POST", "body": { "conference_name": "test" }, "headers": {"Content-Type": "application/json"} }'` – Andrew Oct 26 '20 at 07:04

xims · Answer 4 · 2017-04-20T01:13:02.363

15

Sometimes you don't need third party libraries to parse JSON from text. Sometimes all you need it the following JS command, try it first:

        const res_data = JSON.parse(body);

edited Apr 20 '17 at 01:13

answered Jul 21 '16 at 03:29

xims

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4

The original question is about parsing JSON from a POST message in the Express framework. Without the BodyParser middleware, the JSON data will not exist in the body property of the request object. – ThisClark Nov 07 '16 at 02:39
1

I found this useful, when parsing server response. Thanks! – Hasan Alsawadi Nov 09 '16 at 08:21
1

Thank you Hasan, I appreciate your comment. It did helped me when I was looking for solution and came across this post. Not sure if it works in all cases but it definitely works in some and it is a better solution than using third party library. – xims Nov 11 '16 at 00:48
1

Your answer and a comment provides the answer with more information (the more information being your answer here). You should update your answer to indicate that express needs the body-parser or give an alternative to indicate how body-parser got the data in the first place. – dewwwald Dec 20 '16 at 20:19
3

does not define `body` – jameshfisher Dec 25 '16 at 08:34
But where do I get the string body? – Tomáš Zato - Reinstate Monica Sep 25 '17 at 22:31

score 12 · Answer 5 · answered Apr 17 '19 at 10:18

@Daniel Thompson mentions that he had forgotten to add {"Content-Type": "application/json"} in the request. He was able to change the request, however, changing requests is not always possible (we are working on the server here).

In my case I needed to force content-type: text/plain to be parsed as json.

If you cannot change the content-type of the request, try using the following code:

app.use(express.json({type: '*/*'}));

Instead of using express.json() globally, I prefer to apply it only where needed, for instance in a POST request:

app.post('/mypost', express.json({type: '*/*'}), (req, res) => {
  // echo json
  res.json(req.body);
});

score 11 · Answer 6 · answered Mar 26 '19 at 19:18

11

const express = require('express');
let app = express();
app.use(express.json());

This app.use(express.json) will now let you read the incoming post JSON object

answered Mar 26 '19 at 19:18

SuRa

893
8
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score 0 · Answer 7 · answered Feb 25 '21 at 16:19

0

A beginner's mistake...i was using app.use(express.json()); in a local module instead of the main file (entry point).

answered Feb 25 '21 at 16:19

Hatim

133
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7

How do I consume the JSON POST data in an Express application

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