function isEligible(value,userID) {
  // .. whatever arbitrary logic ..
}

const buckets = [
  user1: new Set(),
  user2: new Set(),
  user3: new Set(),
  user4: new Set()
}

const specialValue = 42;

const count = (
  Object.entries(buckets)
    .filter(([userID,bucket]) => isEligible(specialValue,userID))
    .reduce((counter,[userID,bucket]) => (bucket.add(specialValue),counter+1),0)
);

if (count >= 2) {
  console.log("at least 2 users were eligible for the special value!");
}