The Async Keyword

Just as the await keyword replaces the need for .then(), the async keyword replaces the need to manually write new Promise().

When you prefix a function declaration with the async keyword, two very important things happen:

1. It allows you to use the await keyword inside the function. (You cannot use await inside a normal, synchronous function).
2. It automatically wraps the function’s return value in a Promise.

new Promise() vs async

Here is an older approach creating a Promise manually:

function getPromiseForUserData() {
  return new Promise((resolve) => {
    fetchDataFromServer().then(function(user) {
      resolve(user);
    });
  });
}

And here is the exact same logic using async/await:

async function getPromiseForUserData() {
  const user = await fetchDataFromServer();
  return user; // This is automatically wrapped in a Promise!
}

// When called, both functions return a Promise object
const myPromise = getPromiseForUserData();

Because an async function always returns a Promise, any code that calls your async function must be prepared to await it (or use .then()).