Comment by sfn42

I would have written each statement on its own line:

var users = db.getUsers();

var expiredUsers = getExpiredUsers(users, Date.now());

var expiryEmails = generateExpiryEmails(expiredUsers);

email.bulkSend(expiryEmails);

This is not only much easier to read, it's also easier to follow in a stack trace and it's easier to debug. IMO it's just flat out better unless you're code golfing.

I'd also combine the first two steps by creating a DB query that just gets expired users directly rather than fetching all users and filtering them in memory:

expiredUsers = db.getExpiredUsers(Date.now());

Now I'm probably mostly getting zero or a few users rather than thousands or millions.