block15.js

// books.js
router.get('/:id', (ctx, next) => {
	let getCurrentBook = books.filter(function(book) {
		if (book.id == ctx.params.id) {
			return true;
		}
	});

	if (getCurrentBook.length) {
		ctx.body = getCurrentBook[0];
	} else {
		ctx.response.status = 404;
		ctx.body = 'Book Not Found';
	}
	next();
});