Angular 7 / Express - Null response body on POST request - node.js

Question

I'm trying to get/read the response from a POST request made in Angular 7, if I set the API to return "text" everything is OK, but when i make the response a JSON the response body on Angular is null.
If I try the API on Postman I get full response JSON body.
I tried changing response method on Express API (from the simple res.json() to the "old" way of declaring Content-Type and sending it with res.end()), nothing changed.
The response code I'm using on backend:
res.status(200).json({
success: true,
token: token
})
What I also tried:
res.writeHead(200, { 'Content-Type': 'application/json' })
var json = JSON.stringify({
success: true,
token: token
})
res.end(json)
The service I'm using on Angular:
login(username: string, password: string): Observable<any> {
let body = {username: username, password: password};
let headers = new HttpHeaders();
headers.set('Content-Type', 'application/json');
return this.http.post(this.baseUrl + "/login/sign-in", body, {headers: headers, responseType: 'json', observe: 'response'});
}
The call to that service:
this.api.login("admin", "password").subscribe(result => {
console.log(result);
})
On Postman I get this result:
On Angular I get this (JSON):
On Angular I get this (TEXT):
Edit:
If I add anything before the JSON on the Express app, the body is no more null:
res.writeHead(200, { 'Content-Type': 'application/json' })
var json = JSON.stringify({
success: true,
token: token
})
res.end('some_char' + json)
The result (of course the response goes in error):
Edit 2:
I'm also trying (with no luck) with this simple version of the endpoint:
const express = require('express')
const app = express()
app.post('/login/sign-in', (req, res) => res.json({ value: 1 }))
app.listen(3000, () => {
console.log('App running on port 3000.')
})
Solution:
It was all a CORS problem, I added this to the backend and everything is working fine:
app.use(cors())

Answer 1

Spent a few minutes trying to find out why the body would be empty,
In my case, I had "mode":"no-cors" set in my fetch() options, therefore the returned value from the server would appear as "opaque"
redux fetch body is not use with no cors mode
I hope this can help !