Advanced Async Patterns

Promise.all runs several async operations concurrently and waits for all of them; Promise.race resolves as soon as the first one settles.

const [user, posts] = await Promise.all([
    fetch("/api/user").then((r) => r.json()),
    fetch("/api/posts").then((r) => r.json()),
]);

This runs both requests at the same time rather than one after another — if each takes 1 second, the total wait is about 1 second, not 2.

Common mistakes

• Writing two sequential await calls when the operations don't depend on each other — this needlessly doubles the wait time compared to Promise.all.