mainReducer.js

import {
  GET_POSTS,
  GET_POSTS_SUCCESS,
  GET_POSTS_FAILURE
} from "./../actions/actions";

const INITIAL_STATE = { posts: [], error: null, loading: false, totalpages: 0 };

const Posts = (state = INITIAL_STATE, action) => {
  let error;
  switch (action.type) {
    case GET_POSTS:
      return { posts: [], error: null, loading: true, totalpages: 0 };

    case GET_POSTS_SUCCESS:
      return {
        posts: action.payload,
        error: null,
        loading: false,
        totalpages: action.totalpages
      };

    case GET_POSTS_FAILURE:
      error = action.payload || { message: action.payload.message };
      return { posts: [], error: error, loading: false, totalpages: 0 };

    default:
      return state;
  }
};

export default Posts;