How to access RefImpl data inside js script

I have js code to access data from firebase look like this:

const { user } = getUser();
const { documents: mahasiswa } = getCollection("mahasiswa", ["userId", "==", user.value.uid]);
console.log(mahasiswa);

The output of the console:

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But, how i can access the data inside RefImpl inside of my js code, example:

let angkatan = mahasiswa.angkatan