const err = 'Bad response from server';

// async
const get = async url => {
  const res = await fetch(url, {
    credentials: 'include',
    method: 'GET'
  });
  if (res.status >= 400) {
    throw err;
  }
  let json;
  try {
    json = await res.json();
  } catch(e) {
    if (e.name === 'SyntaxError' && e.message === 'Unexpected end of JSON input') {
      json = {};
    }
    throw e;
  }
  if (!res.ok) {
    throw json.error;
  }
  return json;
};

// promise
const get = url => fetch(url, {
  credentials: 'include',
  method: 'GET'
}).then(res => {
  if (res.status >= 400) {
    throw err;
  }
  return res.json()
  .then(json => ({json, res}))
  .catch(e => {
    if (e.name === 'SyntaxError' && e.message === 'Unexpected end of JSON input') {
      return Promise.resolve({json: {}, res});
    }
    throw e;
  });
}).then(({json, res}) => {
  if (!res.ok) {
    throw json.error;
  }
  return json;
});