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.