Add the original XMLHttpRequest to the Promise catch arguments

New Functionality Requests
#1

The Form’s save method returns a Promise. When the response status is out of the 2xx range we can catch and receive an object with status and statusText.

But sometimes this information is not enough. For example, I’m using API Platform and I can’t get information about what field is throwing a validation error in my back-end.

I guess that could be util to receive also the XMLHttpRequest object, as I show in the example.

var xhr = new XMLHttpRequest();
    xhr.onload = function () {
        if (xhr.status >= 200 && xhr.status < 300) {
            resolve(xhr.response || xhr.responseText);
        } else {
            reject({
                    status: xhr.status, 
                    statusText: xhr.statusText, 
                    xhr     // <--- This could be useful in case we need more information about the response.
               });
              // Or just: 
              // reject(xhr);
       }
};

In my case I could parse xhr.response to get the information I need. I think this could be good for all since sometimes we need to send back a response with specific error messages for multiple fields.