reducer example

reducer.js

import { AUTH_USER, UNAUTH_USER, AUTH_ERROR } from '../actions/types.js';   // types

export default function (state = {}, action) {
  switch (action.type) {                  //set up switch
    case AUTH_USER:
      return { ...state, error: "", authenticated: true };   //  return previous state as spread operator plus updated state
    case UNAUTH_USER:
  return { ...state, authenticated: false };
    case AUTH_ERROR:
      return { ...state, error: action.payload };

  }

  return state;
}