Why, after assignment, an array of objects becomes a string array in which objects are represented as strings?

Question

JavaScript

there is such a function on the server:

function findBooks(res, data = {}, fullBookInfo = null) {
  Book.find(data, (err, books) => {
    if (err) {
      res.json(config.getRespData(true, MSG.internalErr500, err));
    } else if (fullBookInfo === "true") {
      const book = _.clone(books[0]);

      Authors.find(
        { _id: { $in: book.bookInfo.authors } },
        (authorsErr, authors) => {
          if (authorsErr) {
            book.bookInfo.authors = null;
          } else {
            book.bookInfo.authors = [...authors];
          }
        }
      );
      res.json(config.getRespData(false, null, book));
    } else {
      res.json(config.getRespData(false, null, books));
    }
  });
}

here
book.bookInfo.authors = [...authors];
, in theory, an array of objects should be assigned, since authors is an array of objects, but after assignment it becomes a string array in which objects are represented as strings.

["{ createdAt: 2019-10-07T11:43:18.207Z,\n  _id: 
5d666abbe480bd41207b1398,\n  authorName: 'Джордж Мартин',\n  __v: 0 }"]

what could be the problem? I don't understand at all

Answer 1

Are you querying MongoDB? This is all because the database gives you JSON.

Answer 2

Because json needs to be parsed, i.e. decode json string

Answer 3

If the query used Promise, then to get an array of records, you would need to add .toArray() to find().