如何处理CORS错误代码？

Question

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.

Answer 1

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.