newtodos.js

import {combineReducers} from 'redux'

const todos = (state = [], {type, payload}) => {
  switch(type) {
    case LIST_TODOS:
      return payload
    case ADD_TODO:
      return {...state, payload}
    case TOGGLE_TODO:
      return state.map(todo => todo.id === payload ? {...todo, completed: !todo.completed} : todo)
    default:
      return state
  }
}

const isLoading = (state = false, {type}) => {
  switch(type) {
    case FETCH_TODOS:
      return true
    case LIST_TODOS:
      return false
    default:
      return state
  }
}

const filter = (state = 'all', {type}) => {
  switch(type) {
    case FILTER_ALL:
      return 'all'
    case FILTER_COMPLETED:
      return 'completed'
    case FILTER_UNCOMPLETED:
      return 'uncompleted'
    default:
      return state
  }
}

export default combineReducers({
  todos,
  isLoading,
  filter
})