JavaScript Firestore get Added Document ID

Question

How do I get the created firestore document id?

What I have tried with no success: const db = firebase.firestore();

db.collection("my_collection").doc().set({
   data: data
})
.then(docRef => {
    console.log(docRef);
})
.catch((error) => {
    // catch error
});

This always gives me undefined with the docRef

I have also tried the following .then options: .then(function(docRef) { ... } and .then((docRef) => { ... }

Am I missing something?

Thanks in advance.