https://medium.com/p/a7175417f9fd

thunk.js

const updateTitle = title => {
  return async dispatch => {
    dispatch({ type: UPDATE_TITLE });
    try {
      const res = await fetch(url, {
        method: 'PUT',
        headers: {
          'Accept': 'application/json',
          'Content-Type': 'application/json'
        },
        body: { title }
      });
      const json = await res.json();
      dispatch({ type: UPDATE_TITLE_SUCCESS, data: json });
    } catch(err) {
      dispatch({ type: UPDATE_TITLE_FAILED });
    }
  }
}