Note: This article was originally published on October 10, 2017. Some information may be outdated.

async and await landed in ES2017, letting developers write asynchronous code that reads like synchronous steps.

Before: Promise chain

function fetchUser(id) {
  return fetch(`/api/users/${id}`)
    .then(res => res.json())
    .then(data => {
      console.log('User:', data);
    })
    .catch(err => console.error(err));
}

Nested .then() calls grow quickly and push error handling to the end.

After: async / await

async function fetchUser(id) {
  try {
    const res = await fetch(`/api/users/${id}`);
    const data = await res.json();
    console.log('User:', data);
  } catch (err) {
    console.error(err);
  }
}

How it works

• async marks the function, returning a promise automatically.
• await pauses execution until the promise resolves, yielding the result.
• try/catch handles both network errors and thrown exceptions.

Sequential vs parallel

// sequential
await stepOne();
await stepTwo();

// parallel
const [a, b] = await Promise.all([stepOne(), stepTwo()]);

Use Promise.all to start tasks together, then await their combined result.

Tips

• Always wrap awaited code in try/catch for proper error handling.
• Combine with Promise.allSettled for bulk operations where some may fail.
• Keep async functions small; extract chunks to maintain readability.

Async/await became mainstream in 2017, replacing many callback and promise chains with clear top‑to‑bottom control flow.