fetch(): reject when response status is not ok

fetch-helper.js

/**
 * Check for any HTTP errors, and throw if one is encountered.
 * Use as a callback for `fetch` to seamlessly add HTTP error checking to your code.
 * @param {Response} response
 * @example
 * fetch('https://example.com')
 *   .then(checkForHttpErrors)
 *   .then(res => res.json())
 *   .catch(err => { /* process network error or HTTP error */ });
 */
function checkForHttpErrors(response) {
  if (response.ok) return response;
  else throw new HttpError(response);  
}

class HttpError extends Error {
  /**
   * @param {Response} response
   */
  constructor(response) {
    super(response.statusText);
    if (Error.captureStackTrace) {
      Error.captureStackTrace(this, HttpError);
    }
    
    this.response = response;
    this.status = response.status;
  }
}