action.js

import { Todo as TodoTypes } from '../ActionTypes';

export function getAll() {
  return api => ({
    type:    TodoTypes.getAll,
    payload: api('/api/todos')
  });
}

ActionTypes.js

// Generated from a helper in my actual codebase
export default {
  Todos: {
    getAll: {
      begin: 'Todos_getAll_begin',
      end: 'Todos_getAll_end'
    }
  }
}

createStore.js

import { createStore, combineReducers, applyMiddleware } from 'redux';
import * as reducers from '../reducers';

function isFunction(obj) {
  return typeof obj === 'function';
}
function isPromise(obj) {
  return obj && obj.payload && isFunction(obj.payload.then);
}

function promiseMiddleware(api, { dispatch, getState }) {
  return next => function _r(action) {
    if (isFunction(action)) {
      return _r(action(api, getState));
    }
    if (isPromise(action)) {
      const { payload, type, ...rest } = action;

      next({ ...rest, type: type.begin });
      return payload.then(
        result => next({ ...rest, type: type.end, payload: result }),
        error  => next({ ...rest, type: type.end, payload: error, error: true })
      );
    }

    return next(action);
  };
}

export default function (api, initialState) {
  const createStoreWithMiddleware = applyMiddleware(promiseMiddleware.bind(null, api))(createStore);
  const reducer = combineReducers(reducers);

  return createStoreWithMiddleware(reducer, initialState);
}

main.js

import createStore from './createStore';

import request from 'superagent';
import qs from 'qs';
import createStore from './lib/createStore';
import createAPI from './lib/createAPI';

const api = createAPI(({ method, pathname, query = {}, body = {} }) => {
  const url = `http://api.host${pathname}.json`;

  return request(method, url)
    .query(qs.stringify(query))
    .send(body);
});

const store = createStore(api);

reducer.js

export default function todos(state, action) {
  switch (action.type) {
    'Todos_getAll_begin':
      return state.merge({loading: true});
    'Todos_getAll_end':
      return state.merge({loading: false, todos: action.payload});
  }
}