updateStateV1.js

function updateState(dispatch) {
  // helper functions
  const dispatchError = e =>
    dispatch(SET_STATUS({ status: 'error', message: e.message }));

  dispatch(SET_STATUS({ status: 'submitting' }));

  return fetch('https://example.com/api/a')
    .then(() => {
      dispatch(SET_STATUS({ status: 'processing' }));
      return fetch('https://example.com/api/b')
        .then(response => {
          return response
            .json()
            .then(data => {
              dispatch(SET_STATE({ data }));
            })
            .catch(dispatchError);
        })
        .catch(dispatchError);
    })
    .catch(dispatchError)
    .finally(() => {
      dispatch(SET_STATUS({ status: 'finished' }));
    });
}