Empty body in fetch post request

Question

I'm struggling with the fetch API in Javascript. When I try to POST something to my server with fetch method, the request body contains an empty array. But when I use Postman it works. Here is my server-side code in Node.js:

const express = require('express')
const app = express()
const port = 3000

app.use(express.json())
app.post('/api', function (req, res) {
    console.log(req.body)
})
app.listen(port)

Here is my client-side code:

fetch('http://"theserverip":3000/api', {
    method: 'POST',
    headers: { "Content-Type": "application/json" },
    mode: 'no-cors',
    body: JSON.stringify({
        name: 'dean',
        login: 'dean',
    })
})
.then((res) => {
    console.log(res)
})

The problem is that the req.body is empty on server side.

Answer 1

The issue is

mode: 'no-cors'

From the documentation...

Prevents the method from being anything other than HEAD, GET or POST, and the headers from being anything other than simple headers

The simple content-type header restriction allows

• text/plain,
• application/x-www-form-urlencoded, and
• multipart/form-data

This causes your nicely crafted Content-Type: application/json header to become content-type: text/plain (at least when tested through Chrome).

Since your Express server is expecting JSON, it won't parse this request.

I recommend omitting the mode config. This uses the default "cors" option instead.

---

Since your request is not simple, you'll probably want to add some CORS middleware to your Express server.

Another (slightly hacky) option is to tell Express to parse text/plain requests as JSON. This allows you to send JSON strings as simple requests which can also avoid a pre-flight OPTIONS request, thus lowering the overall network traffic...

app.use(express.json({
  type: ['application/json', 'text/plain']
}))

EDIT: Added ending parenthesis to app.use final code block.