JavaScript async/await

Overview

async/await is syntactic sugar over Promises. An async function always returns a Promise. await pauses execution until a Promise settles, without blocking the main thread.

Syntax / Usage

async function loadDashboard(userId) {
  try {
    const user = await fetchUser(userId)
    const posts = await fetchPosts(user.id)
    return { user, posts }
  } catch (error) {
    console.error('Dashboard failed:', error)
    throw error
  }
}

// Parallel requests
async function loadAll() {
  const [users, products] = await Promise.all([
    fetchUsers(),
    fetchProducts(),
  ])
  return { users, products }
}

// Top-level await (ES modules)
const config = await fetch('/config.json').then((r) => r.json())

Examples

Sequential steps with clear error handling:

async function signup(formData) {
  const user = await api.createUser(formData)
  await api.sendWelcomeEmail(user.email)
  return user
}

Loop with await (sequential processing):

async function processFiles(paths) {
  const results = []
  for (const path of paths) {
    results.push(await readFile(path))
  }
  return results
}

Common Mistakes

• Using await in a loop when parallel Promise.all would be faster
• Forgetting try/catch around awaited calls
• Marking non-async functions async unnecessarily
• Awaiting non-Promise values works but adds noise—only await async operations

See Also

promises fetch-api functions closures