How to iterate a JSON array and add data from an async arrow function?

Question

I'm new on MEAN stack and also on JS. What I'm trying to accomplish is to adapt the response that I get from the DB adding to it another field. I have a mongoose method that gave me all the Courses that exist and I want to add to that information all the Inscriptions for each one. So I'm trying this:

exports.getAllCourses = async(req, res) => {
    try {
        const rawCourses = await Course.find();
        const courses = await courseAdapter.apply(rawCourses)
        await res.json({courses});
    } catch (error) {
        console.log(error);
        res.status(500).send("Ocurrio un error imprevisto :/");
    } 
};

My courseAdapter

exports.apply = (courses) => {
    return courses.map(async course=> (
        {
            ...course._doc,
            number: await coursetUtils.getNumberOfInscriptions(course._doc._id)
        }
    ));
}

And my courseUtils:

exports.getNumberOfInscriptions = async courseId => {
       return await CourseInscription.countDocuments({courseId: courseId});
}

I think my problem is with the async-await function because with this code i get this:

{"courses":[
  {},
  {}
]}

or changing some stuff i get this:

{"courses":[
  {"courseInfo":{...},
   "number":{}
  },
  {"courseInfo":{...},
   "number":{}
  }
]}

But never the number of inscription on the response. By the way i use function getNumberOfInscriptions() in other part of my code for make a validation and works.

Answer 1

Trying a lot of stuff i get to this: I change the way I process the data from DB in the apply function and I treat it like an array.

exports.apply = async (courses) => {
    var response = [];
    for (let c of courses) {
        var doc = c._doc;
        var tmp = [{course: doc, inscriptionNumber: await courseUtils.getNumberOfInscriptions(c._doc._id)}];
        response = response.concat(tmp);
    }
    return response;
}

I think is not a pretty good way to accomplish my goal, but it works. If I find something better, performance or clean I will posted.

Anyways I still don't know what I was doing wrong on my previous map function when I call my async-await function. If anybody knows, please let me know.