Async actions in Redux

I think you should be using compose function, so it’s like

import {
  createStore,
  applyMiddleware,
  compose
} from 'redux';
import thunk from 'redux-thunk';
import duedates from './reducers/duedates'

export default compose(applyMiddleware(thunk))(createStore)(duedates);

Thunk allows an action creator to return a function instead of plain-object, so you use it like

export function getDueDates() {
  return dispatch => {
    console.log("IN ACTION");
    fetchDueDates().done(
      dueDates => dispatch(getDueDatesOptimistic(dueDates.entity._embedded.dueDates))
    )
  };
}

You were returning a Promise object, that was one part of the problem. Another part was that redux-thunk hasn’t been properly applied. I bet compose should get the problem solved.