How to extract json using express router?

Question

I am sending a JSON object to my server using post:

 const xhr = new XMLHttpRequest();
 var params = {
     firstname: "Joe",
     lastname: "Bloggs"
 };
 xhr.open('post', '/api/endpoint');
 xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
 xhr.responseType = 'json';
 xhr.addEventListener('load', () => {
     ...
 });
 xhr.send(JSON.stringify(params));

I am using express to handle requests:

...
var app = express();
app.use(bodyParser.urlencoded({ extended: false }));
...

then at my api endpoint I am using Express Router:

const express = require('express');
const router = new express.Router();
router.post('/endpoint', (req, res) => {
    console.log(req.body);
});

When I print out req.body I get the following:

{ '{"firstname":"Joe","lastname":"Bloggs"}': '' }

If I use JSON.parse(req.body) I get the following error:

TypeError: Cannot convert object to primitive value at JSON.parse ()

How can I get the contents of the payload in a format that I can work with, i.e. a json object?

Answer 1

You indicate that you will be sending application/x-www-form-urlencoded here:

xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');

and here you send JSON:

xhr.send(JSON.stringify(params));

which is a clear violation. Make sure that you respect the format you indicated to the server when making your request:

var payload = 'firstname=' + encodeURIComponent(params.firstname) + 
              '&lastname=' + encodeURIComponent(params.lastname);
xhr.send(payload);

If on the other hand you would like to send JSON content then you could add the corresponding body parser on the server:

app.use(bodyParser.json({ type: 'application/json' }))

then set the proper Content-Type request header on the client:

xhr.setRequestHeader('Content-type', 'application/json');

and now you can JSON.stringify when sending the request:

xhr.send(JSON.stringify(params));

at the api endpoint, the JSON can then be extracted from req.body (no need to use JSON.parse)