Promise.allSettled() and Promise.race()

Promise.allSettled waits for every outcome and reports success or failure for each. Promise.race settles as soon as the first input settles, whether fulfilled or rejected. These methods answer different coordination questions.

Reading the code: allSettled produces statuses fulfilled and rejected without throwing for the rejected member. In the race, the resolved fast promise wins; the second promise never settles, but does not keep Node alive.

Keep the boundary clear: Do not use Promise.race as cancellation. Losing promises still run unless an API provides explicit cancellation.

Save the code as promise-allsettled-promise-race.ts. The result below was captured after compiling this exact example with strict TypeScript checking and executing the emitted JavaScript in Node.js.

TypeScript code

async function main(): Promise<void> {
  const outcomes = await Promise.allSettled([Promise.resolve("ok"), Promise.reject("missing")]);
  console.log(outcomes.map(result => result.status).join(","));
  const first = await Promise.race([Promise.resolve("fast"), new Promise<string>(() => {})]);
  console.log(first);
}
main().catch(console.error);

Verified output

fulfilled,rejected
fast

Build: npx tsc --strict --target es2022 --module commonjs --lib es2022,dom,esnext.disposable promise-allsettled-promise-race.ts; run: node promise-allsettled-promise-race.js. The exact filename may be changed freely. When a multi-file project exists, prefer its tsconfig.json and build scripts.

allSettled produces statuses fulfilled and rejected without throwing for the rejected member. In the race, the resolved fast promise wins; the second promise never settles, but does not keep Node alive.

The output shown above comes from the initialized values in this program. Replacing a type annotation alone does not transform a JavaScript value.

Do not use Promise.race as cancellation. Losing promises still run unless an API provides explicit cancellation.

Check both the TypeScript diagnostic and the emitted JavaScript behavior. A program can compile correctly and still need runtime validation or error handling.

Inspect the status discriminator and print the value or reason for each allSettled result.

Before running your change, write down the type you expect TypeScript to infer and the output you expect JavaScript to print. Then check both predictions.

Promise.

Try the practice change and re-run the exact program to test your understanding.