/**
 * Gets what should be in the `response` property of the XHR. However,
 * since we still support the final versions of IE, we need to do a little
 * checking here to make sure that we get the right thing back. Conquentally,
 * we need to do a JSON.parse() in here, which *could* throw if the response
 * isn't valid JSON.
 *
 * This is used both in creating an AjaxResponse, and in creating certain errors
 * that we throw, so we can give the user whatever was in the response property.
 *
 * @param xhr The XHR to examine the response of
 */
export function getXHRResponse(xhr: XMLHttpRequest) {
  switch (xhr.responseType) {
    case 'json': {
      if ('response' in xhr) {
        return xhr.response;
      } else {
        // IE
        const ieXHR: any = xhr;
        return JSON.parse(ieXHR.responseText);
      }
    }
    case 'document':
      return xhr.responseXML;
    case 'text':
    default: {
      if ('response' in xhr) {
        return xhr.response;
      } else {
        // IE
        const ieXHR: any = xhr;
        return ieXHR.responseText;
      }
    }
  }
}