You do not —> AWAIT on frontend.
By the way, you do not need to code on backend, to get the email of current logged-in-user.
You can do it also on front-end.
The only advantage of the back-end-version is the higher security i think.
$w.onReady(async ()=>{
let userEmail = await getEmail();
let newQuizTaker = {'email' : userEmail, 'attempt': 5, 'score': 0}
});