QJavaScript · Interview preparation
How does async/await work in JavaScript?
An async function always returns a Promise, and await pauses that function until the awaited value settles.
The idea to remember.
An async function always returns a Promise, and await pauses that function until the awaited value settles. Other scheduled JavaScript work can continue while the function is waiting.
01Learn by doing
From first example to real project.
Start with the smallest working idea, examine a more detailed example, then look at a real application pattern. Adapt dependencies, error handling and data models to your project.
Basic: promise resolution
01 / BEGINNERPromise callbacks run after synchronous code.
console.log('A');
Promise.resolve().then(() => console.log('C'));
console.log('B'); // A, B, CIntermediate: await and errors
02 / INTERMEDIATEHandle unsuccessful HTTP responses as well as rejected requests.
async function loadUser(id) {
const response = await fetch('/api/users/' + id);
if (!response.ok) throw new Error('Unable to load user');
return response.json();
}Real scenario: parallel independent calls
03 / REAL SCENARIOPromise.all starts independent calls together and handles failures.
async function loadDashboard() {
const [account, activity] = await Promise.all([
fetch('/api/account').then(r => { if (!r.ok) throw Error('Account'); return r.json(); }),
fetch('/api/activity').then(r => { if (!r.ok) throw Error('Activity'); return r.json(); })
]);
return { account, activity };
}02Check your understanding
Try it in your own words.
Explain how does async/await work in JavaScript without looking at the code. Then modify the intermediate example, describe one trade-off and identify when the real-world pattern fits.
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