Promise.all
Wait for several promises to finish together.
Syntax
const results = await Promise.all([p1, p2]);Promise.all() takes an array of promises and resolves once all of them have resolved, giving you an array of their results.
Why use it
It runs asynchronous tasks in parallel and waits for the whole group, instead of awaiting each one in sequence.
Example
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When to use it
- Fetch a user's profile, orders, and notification count in parallel and render the dashboard once all three arrive.
- Upload multiple files concurrently with Promise.all instead of uploading them sequentially.
- Use Promise.allSettled to run several independent API calls and handle each result even if some fail.
More examples
Promise.all for parallel fetches
Runs two fetch calls in parallel and destructures the resolved values once both complete.
async function loadDashboard() {
const [user, orders] = await Promise.all([
fetch("/api/user/1").then(r => r.json()),
fetch("/api/orders?userId=1").then(r => r.json())
]);
console.log(user.name, orders.length);
}Promise.allSettled for fault tolerance
Uses Promise.allSettled to process all promises regardless of failures, logging each status.
const results = await Promise.allSettled([
Promise.resolve("data A"),
Promise.reject(new Error("B failed")),
Promise.resolve("data C")
]);
results.forEach(r => console.log(r.status, r.value ?? r.reason?.message));Promise.race for timeout guard
Uses Promise.race to reject with a timeout error if the fetch does not complete within 3 seconds.
function withTimeout(promise, ms) {
const timeout = new Promise((_, reject) =>
setTimeout(() => reject(new Error("Timed out")), ms));
return Promise.race([promise, timeout]);
}
withTimeout(fetch("/api/data"), 3000)
.catch(e => console.error(e.message));
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