Extract Function

The function below does too many things at once — it validates, transforms and formats all in one block.

Refactor solve(users) by extracting helper functions so each function does exactly one thing. The output must be identical.

// dirty
function solve(users) {
  const result = [];
  for (const u of users) {
    if (u.age >= 18 && u.email.includes('@') && u.name.trim().length > 0) {
      result.push({ name: u.name.trim(), email: u.email.toLowerCase(), adult: true });
    }
  }
  return result;
}

Your extracted version should have at minimum: isValid(user), formatUser(user), and the main solve(users) that composes them.