深拷贝Object 添加一个key：value

Question

I am pre-fetching a product from a database using mongoose with next.js and react-query . I was wondering why I need to do a deep copy of a nested object in order to add a key:value to it. Otherwise it does not work. Let me know what I am not understanding.

await queryClient.prefetchQuery(['productSlug', slug], async () => {
  const product = await read(slug);

  const existingRatingObject = product.ratings.find(
    (item) => item.postedBy.toString() === user._id.toString()
  );
  const copyProduct = JSON.parse(JSON.stringify(product));

  if (existingRatingObject) {
    copyProduct.star = existingRatingObject.star;
  } else {
    copyProduct.star = 0;
  }

  console.log({ copyProduct });
  return JSON.stringify(copyProduct);
});

Answer 1

The reason is that the product fetched is a Mongoose document not a plain old JavaScript object.

When you convert it to plain old javascript Object, you will be able to add any key to it.

You can add.lean() to you query or add toObject/toJSON to you the fetched document