TypeError: undefined is not an object (evaluating 'state.favoriteBooks.findIndex')

Question

每次我按收藏夹按钮时都会出现错误。

TypeError: undefined is not an object  (evaluating 'state.favoriteBooks.findIndex')

这个错误发生在book.js redux reducer:

import { SET_BOOKS, TOGGLE_FAVORITE } from '../actions/types';

import Book from '../../models/book';

const initialState = {
  books: [],
  favoriteBooks: [],
};

export default (state = initialState, action) => {
  switch (action.type) {
 
case SET_BOOKS:
  return {
    books: action.books,
  };

    case TOGGLE_FAVORITE:
      const existingIndex = state.favoriteBooks.findIndex(
        (book) => book.id === action.bookId
      );
      if (existingIndex >= 0) {
        const updatedFavBooks = [...state.favoriteBooks];
        updatedFavBooks.splice(existingIndex, 1);
        return { ...state, favoriteBooks: updatedFavBooks };
      } else {
        const book = state.books.find((book) => book.id === action.bookId);
        return { ...state, favoriteBooks: state.favoriteBooks.concat(book) };
      }

    default:
      return state;
  }
};

我认为问题在于它试图在变量为空时查找索引。但是当我 运行 调度 toggleFavorite(BookId) 时，它正在放入书 ID。

Answer 1

在SET_BOOKSreturn我忘了加..state。

 ...
    case SET_BOOKS:
  return {
    ...state,
    books: action.books,
  };
...

不要忘记添加 ...state，因为您想在 initialState 中保存以前的状态。这就是为什么它没有在 books.

中获取任何 ID