Async / Await

async and await are the modern way to work with Promises. They let you write asynchronous code that looks and reads like regular synchronous code — no more long chains of .then().

async function

Adding async before a function makes it return a Promise automatically.

async function greet() {
  return 'Hello!'
}

greet().then(console.log) // 'Hello!'

await

Inside an async function you can use await to pause and wait for a Promise to resolve. The value you get back is the resolved value — not the Promise itself.

async function loadUser() {
  const response = await fetch('https://jsonplaceholder.typicode.com/users/1')
  const user = await response.json()
  console.log(user.name)
}

loadUser()

Compare this to the same code written with .then() chains — much easier to read.

Error handling with try / catch

Wrap your await calls in a try / catch block to handle errors:

async function loadUser(id) {
  try {
    const response = await fetch(
      `https://jsonplaceholder.typicode.com/users/${id}`
    )
    if (!response.ok) {
      throw new Error(`Request failed: ${response.status}`)
    }
    const user = await response.json()
    console.log(user.name)
  } catch (error) {
    console.log('Something went wrong:', error.message)
  }
}

loadUser(1)

Promise.all

If you need to run several async operations at the same time and wait for all of them, use Promise.all. It runs them in parallel and resolves when every one of them has finished.

async function loadMultiple() {
  const [user, post] = await Promise.all([
    fetch('https://jsonplaceholder.typicode.com/users/1').then((r) => r.json()),
    fetch('https://jsonplaceholder.typicode.com/posts/1').then((r) => r.json()),
  ])

  console.log(user.name)
  console.log(post.title)
}

loadMultiple()

If any of the Promises rejects, Promise.all rejects immediately with that error.

Promise.allSettled

Promise.allSettled is like Promise.all but it waits for all Promises to finish, even if some fail. Each result tells you whether it was fulfilled or rejected.

async function tryAll() {
  const results = await Promise.allSettled([
    fetch('https://jsonplaceholder.typicode.com/users/1').then((r) => r.json()),
    fetch('https://bad-url-that-does-not-exist.xyz').then((r) => r.json()),
  ])

  results.forEach((result) => {
    if (result.status === 'fulfilled') {
      console.log('Success:', result.value)
    } else {
      console.log('Failed:', result.reason)
    }
  })
}

tryAll()

Use Promise.allSettled when you want all results regardless of failures.