reducer_example.js

import { SET_BOOKNAME, ADD_BOOKMARK, DELETE_BOOKMARK } from '../actions/types';

export default function bookmarksReducer(state = {book_name: "", list: []}, action) {
  switch (action.type) {
    case SET_BOOKNAME:
      return {...state, book_name: action.payload}
      // copy the current state 
      // and change the value of book_name property
      // with payload property given by the action
    case ADD_BOOKMARK:
      return {...state, list:[...state.list, action.payload]}
      // copy the current state
      // make a new list out of the list in the current state
      // concatenate the copied list with the payload of the action
    case DELETE_BOOKMARK:
      return {...state, list: state.list.filter(bookmark => bookmark.id !== action.payload.id)}
      // The Array.filter method returns a new array from the original
      // Like the Array.maps methods for instance
      // This is one of the case where JS does immutability OK out of box
    default:
      return state;
  }
}