fetchMiddleware.js

const FETCH = '@@middleware/fetch/FETCH';

export default (baseUrl, fetchImplementation) => () => next => async action => {
  if (action.type === FETCH) {
    const { method, path, body } = action;
    const params = { method };
    if (body) params.body = JSON.stringify(body);
    const url = baseUrl + path;

    const response = await fetchImplementation(url, params);
    if (!response.ok) throw new Error('Failed to fetch');

    const responseBody = await response.json();
    return responseBody;
  } else {
    next(action);
  }
}

export const fetchJson(method, path, body) => ({
  type: FETCH,
  method,
  path,
  body,
});