oldtodos.js

const initialState = {
  todos: [],
  filter: 'all',
  isLoading: false
}

export default function(state = initialState, action) {
  switch (action.type) {
    case FETCH_TODOS:
      return {...state, isLoading: true}
    case LIST_TODOS:
      return {...state, todos: action.payload, isLoading: false}
    case ADD_TODO:
      return {...state, todos: {...state.todos, action.payload}}
    case TOGGLE_TODO:
      return {...state, todos: state.todos.map(todo => todo.id === action.payload ? {...todo, completed: !todo.completed} : todo)}
    case FILTER_ALL:
      return {...state, filter: 'all'}
    case FILTER_COMPLETED:
      return {...state, filter: 'completed'}
    case FILTER_UNCOMPLETED:
      return {...state, filter: 'uncompleted'}
    default:
      return state
  }
}