Async/await used consistently

Mixing .then() chains and async/await in the same codebase — or in the same function — creates inconsistent error propagation: .then() chains require .catch() while async/await uses try/catch, and mixing them means some rejections are caught by one mechanism and some by the other. ISO 25010:2011 §6.5.2 classifies this as a maintainability defect. Nested .then() chains also re-introduce the callback-pyramid problem that async/await was designed to solve, making control flow harder to read and independent async operations sequential when they could run in parallel.

Standardize on async/await throughout. Use Promise.all() for genuinely independent async operations — never await them sequentially when they don't depend on each other's results.

// Bad: nested .then() chains, mixed with async
async function loadUserData(id: string) {
  return fetchUser(id)
    .then((user) => fetchUserPosts(user.id)
      .then((posts) => ({ user, posts })))
    .catch((err) => console.error(err))
}

// Good: consistent async/await
async function loadUserData(id: string) {
  try {
    const user = await fetchUser(id)
    const posts = await fetchUserPosts(user.id)
    return { user, posts }
  } catch (err) {
    logger.error('Failed to load user data', err)
    throw err
  }
}

// Good: parallel operations with Promise.all
async function loadDashboard(userId: string) {
  const [user, posts] = await Promise.all([
    fetchUser(userId),
    fetchUserPosts(userId),
  ])
  return { user, posts }
}