JAVASCRIPT

fetch 500 internal server error

Error on app.js:5581 - Error about fetch
POST http://localhost:8080/login 500 (Internal Server Error)

To understand any type of internal server errors, you can check your network.
On web browser, click on inspect network and on the network error that appears, 
click on the login file and you see the error in the options of everything, 
fetch/xhr, js... 

Or in another cases, your redirect has an mistake.