Identify failed Pre-flight request ( CORS issues )

[Satrajit]

Whenever the browser makes a preflight request (HTTP OPTIONS call) in certain cases and If the response of the preflight request fails the protocol checks ( no response / response not as expected ), the actual request ( GET / POST ) is not made and the XHR errors out with status code 0 in such cases.

Those cases return status code as 0. Is there any way to identify preflight request failure scenarios or any API to capture the preflight request failure (as there can be other reasons for getting the status code as 0) ?
Main motive is to differentiate other errors with the preflight failures.

[Satrajit]

@magreenblatt any API that can be used for this cause?

[magreenblatt]

Are there any error messages written to the JS console?

[Satrajit]

Access to XMLHttpRequest at 'https://xxx/config.json' from origin 'http://localhost:8000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status.

This is the error message on JS console.
The status code returned is 0

But is there any way for CEF to differentiate this preflight request error ?

[magreenblatt]

Not that I'm aware of. See here for background.