Return Array undefined with an async function with firestore

Question

I have a function that i want to return filled array with values from firestore bd, but i need to wait for foreach for this array filled correctly.

I try some methods from this website but I can't understand what I'm doing bad.

My function is:

static async assistencia(id) {
    console.log('Get Assistència ' + id);
    let alumnesId = id;
    var assistenciaAlumne = [];

    db.collection('alumnes')
        .doc(alumnesId)
        .collection('assistencia')
        .get()
        .then((assistencia) => {
            const promises = [];
            assistencia.forEach((assistenciaDoc) => {
                assistenciaAlumne.push([assistenciaDoc.id, assistenciaDoc.data().assistencia]);
                promises.push(db.collection('alumnes').doc(alumnesId).collection('assistencia').get());
            });
            return Promise.all(promises);
        })
        .then(function () {
            return assistenciaAlumne;
        })
        .catch((error) => {
            console.log(error);
        });
}

And I call this function with a button with this code:

var array = Alumnes.assistencia('0qSzBxVimwRlurLHNzXp');
    console.log(' array', array);

Yes, Alumnes it's a class.

The basic problem is that this array returns on console:

array 
Promise {<resolved>: undefined}
    __proto__: Promise
    [[PromiseStatus]]: "resolved"
    [[PromiseValue]]: undefined

What I'm doing wrong?

Answer 1

Right now you return a value from the then() , but nobody does anything value. To return it from assistencia you need to bubble up the return value.

return db.collection('alumnes')
  ...