Promise.all, Promise.race, Promise.allSettled, Promise.any explained

Running Multiple Promises Concurrently

The four static Promise combinators handle different patterns for running multiple async operations together. Choosing the right one avoids unnecessary serial execution and handles partial failures correctly.

Promise.all — All Must Succeed

const [a, b, c] = await Promise.all([op1(), op2(), op3()]);
// Rejects immediately if ANY operation rejects — fail-fast

Promise.allSettled — Get All Results Regardless

const results = await Promise.allSettled([op1(), op2(), op3()]);
results.forEach(r => {
  if (r.status === "fulfilled") console.log(r.value);
  else console.error(r.reason);
});
// Never rejects — every result is inspectable

Promise.race — First to Settle Wins

function withTimeout(promise, ms) {
  const timeout = new Promise((_, reject) =>
    setTimeout(() => reject(new Error("Timeout")), ms)
  );
  return Promise.race([promise, timeout]);
}
// Resolves or rejects with whichever settles first

Promise.any — First to Succeed Wins

const fastest = await Promise.any([server1(), server2(), server3()]);
// Rejects only if ALL fail, with an AggregateError

Choosing the Right Combinator

Use all when every result is required and one failure should abort the whole operation. Use allSettled for batch jobs where partial failures are acceptable. Use race to implement timeouts or take whichever resource responds first. Use any when you have redundant sources and one success is sufficient.