Getting the Request Body in Express

Express doesn’t automatically parse the HTTP request body for you,
but it does have an officially supported middleware package for parsing HTTP request bodies. As of v4.16.0, Express comes with a built-in JSON request body parsing middleware that’s good enough for most JavaScript apps.

JSON Request Body

Express has a built-in express.json() function that returns an Express middleware function that parses JSON HTTP request bodies into
JavaScript objects. The json() middleware
adds a body property to the Express request req.
To access the parsed request body, use req.body as shown below.

const
 express = 
require
(
'express'
);
const
 app = express();

 
 
app.use(express.json());

app.post(
'*'
, (req, res) => {
  req.body;  
  res.json(req.body);
});
const
 server = 
await
 app.listen(
3000
);

 
const
 axios = 
require
(
'axios'
);
const
 res = 
await
 axios.post(
'http://localhost:3000/'
, {
  
answer
: 
42
});
res.data; 

Common Gotchas

If the JSON body is malformed, Express will error out with an HTTP 400. This
error also triggers error handling middleware.

const
 express = 
require
(
'express'
);
const
 app = express();
app.use(express.json());
app.post(
'*'
, (req, res) => {
  res.json(req.body);
});

 
 
app.use(
function
(
err, req, res, next
) {
   
  err.message;
  next(err);
});
const
 server = 
await
 app.listen(
3000
);

 
const
 axios = 
require
(
'axios'
);
const
 headers = { 
'Content-Type'
: 
'application/json'
 };
const
 err = 
await
 axios.
  post(
'http://localhost:3000/'
, 
'not json'
, { headers }).
  then(
()
 => 
null
, err => err);

 
 
err.response.status;  
err.message; 

It is important to note that, by default, the json() middleware ignores
any request whose Content-Type header isn’t something that Express
recognizes as JSON. If express.json() is silently ignoring your request,
make sure you check the Content-Type header.

const
 express = 
require
(
'express'
);
const
 app = express();
app.use(express.json());
app.post(
'*'
, (req, res) => {
   
   
  req.body;
  res.json(req.body);
});
const
 server = 
await
 app.listen(
3000
);

 
const
 axios = 
require
(
'axios'
);
const
 headers = { 
'Content-Type'
: 
'text/plain'
 };
const
 res = 
await
 axios.
  post(
'http://localhost:3000/'
, 
'not json'
, { headers });

res.data; 

URL-Encoded Form Body Parser

Express has an officially supported module body-parser that includes a
parser for URL-encoded request bodies, like the ones submitted by HTML forms.

const
 express = 
require
(
'express'
);
const
 app = express();
app.use(
require
(
'body-parser'
).urlencoded({ 
extended
: 
false
 }));
app.post(
'*'
, (req, res) => {
  req.body;  
  res.json(req.body);
});
const
 server = 
await
 app.listen(
3000
);

 
const
 axios = 
require
(
'axios'
);
const
 headers = {
  
'Content-Type'
: 
'application/x-www-form-urlencoded'
};
const
 res = 
await
 axios.
  post(
'http://localhost:3000/'
, 
'answer=42'
, { headers });

res.data; 

Files

Neither Express nor body-parser supports file uploads out of the box.
However, you can use the Formidable module on npm to handle file uploads. You can learn how
on our tutorial on file uploads with Express.

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