json-merge-patch.js

app.patch("/books/:id", (req, res) => {
	// Attempt to find the book.
	let book = findBook.get({ id: req.params.id });

	// If the book doesn't exist, send an error.
	if (!book) {
		res.status(404).json({ errors: ["Book not found"] });
		return;
	}

	// Otherwise, update the book.
	const updates = { ...book, ...req.body };
	updateBook.run(updates);
	book = findBook.get({ id: req.params.id });
	res.status(200).json(book);
});