The problem asked to rewrite function `activeEmails` in such way that it does not use 'for' keyword or calls `push()`. Here is how you can do this:
```ts
export interface User {
  email: string;
  active: boolean;
}

/** The lowercased addresses of the active users, in order. */
export function activeEmails(users: readonly User[]): string[] {
    return users.filter(user => user.active).map(user => user.email.toLowerCase());
}
```