PouchDB get document returns undefined

The pouchDB get document is returning an undefined value

function getVal(db, id) {
    if (db == "lvldb") {
        lvldb.get(db.toString()).then(function (doc) {
            if (id == null) {
                return doc;
            } else {
                return doc[id];
            }
        });
    }
}

There is no error but when I view what the function returns it says undefined