What is the difference between Promise.all, allSettled, race and any?

These combinators answer different concurrency questions. The key differences are whether failures reject the combined promise and whether you need every result or just the first one.

const a = Promise.resolve("a");
const b = Promise.reject(new Error("b failed"));

await Promise.all([a, b]); // rejects with "b failed"
await Promise.allSettled([a, b]);
// [{ status: "fulfilled", value: "a" },
//  { status: "rejected", reason: Error("b failed") }]

await Promise.race([a, b]); // "a"
await Promise.any([b, a]); // "a"

Which one to use

• Promise.all when every result is required and one failure should abort the operation
• Promise.allSettled when you want every outcome, including failures
• Promise.race when the first settled promise should win, including a timeout
• Promise.any when the first success is enough and failures can be ignored until all fail

Promise.any rejects with an AggregateError only when every input rejects. That error contains the individual reasons.

function withTimeout(promise, ms) {
  const timeout = new Promise((_, reject) => {
    setTimeout(() => reject(new Error("timeout")), ms);
  });

  return Promise.race([promise, timeout]);
}