“Filtr-VS-Map-Reactjs-i-JSX” Kod odpowiedzi

Filtr-VS-Map-Reactjs-i-JSX

{              
  books && books
    .filter(book => book.shelf.toLowerCase().includes(shelf.toLowerCase()))
    .map((book, index) => {
      return (
        <Book
           key={book && book.id ? book.id : index}
           changeShelf={this.props.changeShelf}
           book={book} />
      );
    })
}