How to convert Mongoose docs to JSON with Node.js?

To convert Mongoose docs to JSON with Node.js, we use the lean method.

For instance, we write

UserModel.find()
  .lean()
  .exec((err, users) => {
    return res.end(JSON.stringify(users));
  });

to call lean to convert the results returned from find to a plain object.

Then we get the results from the users parameter in the exec callback.

users is a plain JavaScript array.