Empty body in fetch POST request

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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.

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