code: function routerReducer() {
    var state = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : initialState;
  
    var _ref = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {},
        type = _ref.type,
        payload = _ref.payload;
  
    if (type === LOCATION_CHANGE) {
      return _extends({}, state, { locationBeforeTransitions: payload });
    }
  
    return state;
  }
docs: This reducer will update the state with the most recent location history
  has transitioned to. This may not be in sync with the router, particularly
  if you have asynchronously-loaded routes, so reading from and relying on
  this state is discouraged.