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How can a JS script capture the details of a CORS request failure? [duplicate]

Is it possible to get the error code of a failed preflight request so that I can print a meaningful error message? (Or is there a habit of printing a static error for all failed preflight requests no matter the code?)
Clearly, the status code 401 is printed to the console, but the error handler or a .catch() statement only receive the error object thrown.
If I remove the header that triggers the preflight, I get to handle the response myself and I can extract the status code.
// also note that the returned code 401 in first screenshot is wrong. But that's another question..

No, it isn't.
If the status code of the preflight response is not 200, then the Same Origin Policy will prevent any information about the response from being extracted from it.
I've just finished setting up a web API to always return 200 OK status for OPTIONS requests for this reason.

Unfortunately not. All fetch returns is a TypeError with message "Failed to fetch".
> fetch('https://stackexchange.com/404').then(x => console.info(x), error => console.error(error))
× TypeError: Failed to fetch
I tried to manually send another preflight-request and grab the response code of that.
> fetch('https://stackexchange.com/404', { method: 'OPTIONS' }).then(x => console.info(x), error => console.error(error))
× TypeError: Failed to fetch
But that just triggers another preflight and still doesn't let me at the actual failed request.

403 error when I try to make a request to my backend from my frontend although I set `Access-Control-Allow-Origin` to "*"`

I have a problem that has been blocking me for several days and I don't understand where it comes from.
I have read a lot on the internet and I can't find a solution to solve my problem exactly.
I'll start: I just implemented a frontend/backend solution that I've just deployed in production. My backend and frontend are in a different port each. However, I got the famous error No 'Access-Origin' header is present on the requested resource.
I managed to solve this problem by adding an Access-Control-Allow-Origin header in Nginx:
more_set_headers 'Access-Control-Allow-Origin: *';
The error disappeared after that, then I got an error but in Axios this time. It is a 403 error ERR_BAD_REQUEST - Request failed with status code 403 - Invalid CORS request.
So here I am, I despair a bit.
I added this code in AXIOS in order to give it the header (axios.js) :
export default boot(async ({ app }) => {
axios.defaults.headers.common["Access-Control-Allow-Origin"] = "*";
});
But it still doesn't work.
So I analyzed the response I get when I send the request and here it is:
I saw that there was as Referrer-Policy: strict-origin-when-cross-origin
So I tried to change this mode, by adding it in the headers and it didn't work. And I changed this mode in my browser and it still doesn't work.
So here's the thing, can anybody help me? I don't expect an answer but I really can't understand what's blocking and it's bothering me in my debugging.
What are the CORS missing ? How and where I can add them ?

openstack identity api get response error code

im intern student. I have a question .
Im working to bug/fix on an Openstack cloud , Javascript and nodejs web app. Now im fixing toastr.error messages and then translate message's language.
How can i get openstack-identity-api response error code ? I have some documents about error code's reason like this.
Code Reason
204 - No Content The server has fulfilled the request.
Error¶
Code Reason 400 - Bad Request Some content in the request was invalid
401 - Unauthorized User must authenticate before making a request.
403 - Forbidden Policy does not allow current user to do this
operation.
404 - Not Found The requested resource could not be found.
409 - Conflict This operation conflicted with another operation on
this resource.
https://developer.openstack.org/api-ref/identity/v3/?expanded=change-password-for-user-detail
Example :
if(resp.error === 401){
toastr.error("Authentication failure. Please contact the system administrator.");}

Could you please explain your ask here? The Openstack API document you have referred clearly shows the response codes and what might be the cause for each error code. What additional info you would require?

Trying to GET some resource returns net::ERR_EMPTY_RESPONSE for Angular.js

So I re-installed my database, the problem is that now, my app doesn't seem to work.
Every time I try to GET a resource in my Angular.js site, the request stalls until I get back this error:
net::ERR_EMPTY_RESPONSE
The preflight "OPTIONS" requests works fine, but the actual GET request just hangs up.
If I try the same GET request with curl, then I instantly get a correct response. The same for the browser, if I type the request in the address bar, I get a correct response.
What do you guys think may be happening here?

How to handle CORS error code?

Edit: I just realized this is a duplicate of Recommended solution for AJAX, CORS, Chrome & HTTP error codes (401,403,404,500), and he tried the idea I propose at the end. But I can't tell if he succeeded (dud user?), and no one else has posted a solution or even a comment, so I think it's worth fishing for new answers.
Problem:
I send a properly-executed (edit: IMproperly-executed. End of story...) CORS request.
The server receives the request and attempts to process it.
The server returns an error response, for example a 422 Unprocessable Entity, along with JSON information about the errors. The idea is that my app could receive this error information and handle it appropriately in the UI.
The browser blocks my error handler from getting the response content, or even getting the status code.
Showing that the browser received the 401 status code but treated it as a CORS security error:
The response object, showing that my code cannot access the response data (data: "", status: 0):
How have other people handled this limitation? My best guess right now is to hijack an HTTP "success" code (2XX) as an error code, and then include the error information in the response. This prevents me from using the ajax error handlers in a normal way, but I'm handling this as a global ajax filter anyway, so this filter would capture the deviant success code and trigger the error handlers instead.

The console message indicates that the server isn't sending the required Access-Control-Allow-Origin header when it sends the 401 response code.
You won't be able to use the CORS error handler to inject content into the DOM unless you fix that.
The server is likely sending the header correctly on responses with a 200 response code. It needs to do it for other response codes, though, if you wish to use data from those response codes.
Fix that on the server end before making design compromises on the client side. That may solve your problem straight away.

It seems it's an opaque response where you can't obtain the headers or the response. And everything is set to null or empty.
https://developer.mozilla.org/en-US/docs/Web/API/Response/type
Or maybe in the server you should add:
Access-Control-Allow-Origin: *

Very late answer but in case someone wants to check whether an error occurred while sending an XMLHttpRequest and then take appropriate actions (on the CLIENT side), then this is a quick workaround:
try{
request.send();
}catch(err){
if(e.toString().startsWith("NetworkError")){
//pasre the string to check error code
//and take appropriate actions
}
}
This is needed because the onreadystatechange function doesn't get executed when a NetworkError occurs and, in fact, the whole script is terminated.