Handling POST Requests with Express

Express makes it easy to register route handlers for POST requests. Here’s a basic POST request
handler.

const
 express = 
require
(
'express'
);
const
 app = express();app.post(
'/'
, 
function
 
requestHandler
(
req, res
) {  res.end(
'Hello, World!'
);});
const
 server = 
await
 app.listen(
3000
);

The above code starts an Express server on port 3000 that handles POST requests to the / endpoint. You can then
send requests to the server using an HTTP client like Axios

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

JSON Request Bodies

POST requests requests are different from GET requests because POST requests are allowed to send data in the HTTP request body. For example, the below code sends an HTTP POST request with a JSON object in the request body:

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

Express doesn’t parse HTTP request bodies by default, but it does have a built-in middleware that populates the req.body property with the parsed request body. For example, app.use(express.json()) is how you tell Express to automatically parse JSON request bodies for you.

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; 

URL Encoded Request Bodies

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; 

POST requests are often used for file uploads. Express itself doesn’t make it easy to upload files, but there are several npm modules that handle file uploads for you. Formidable is the most popular file uploading library for Express. Here’s how you can use Formidable to upload files:

const
 app = 
require
(
'express'
)();
const
 formidable = 
require
(
'formidable'
);
const
 fs = 
require
(
'fs'
);app.post(
'/upload'
, 
function
(
req, res
) {  
const
 form = 
new
 formidable.IncomingForm();     form.parse(req, 
function
(
err, fields, files
) {    
if
 (err != 
null
) {      
console
.log(err)      
return
 res.status(
400
).json({ 
message
: err.message });    }              
const
 [firstFileName] = 
Object
.keys(files);    res.json({ 
filename
: firstFileName });  });});
const
 server = 
await
 app.listen(
3000
);

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Espresso supports:

• Route handlers, like `app.get()` and `app.post()`
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• Express 4.0 style subrouters

As a bonus, Espresso also supports async functions, unlike Express.

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