reducer.js

const ADD_TODO = 'add_todo';
const ADD_TODO_SUCCESS = 'add_todo_success';
const ADD_TODO_ERROR = 'add_todo_error';

const initialState = {
  loading: false,
  error: null,
  data: [],
}

const reducer = (state = initialState, action) => {
  switch (action.type) {
    case ADD_TODO:
      return { loading: true, error: null, data: [] };

    case ADD_TODO_SUCCESS:
      return { loading: false, error: null, data: action.payload };

    case ADD_TODO_ERROR:
      return { loading: false, error: action.payload, data: [] };

    default:
      return state;
  }
};

export default reducer;