Concurrency patterns (all/settled/race) types

async function one(): Promise<number> { return 1 }
async function two(): Promise<string> { return "two" }

async function runAll() {
  const [a, b] = await Promise.all([one(), two()]);
  // a: number, b: string
  console.log(a + 1, b.toUpperCase());
}

runAll();

async function fetchItem(id: number): Promise<string> {
  return `item-${id}`;
}

async function getMany(ids: number[]): Promise<string[]> {
  const tasks = ids.map(id => fetchItem(id)); // start all
  return Promise.all(tasks); // await all
}

getMany([1,2,3]).then(xs => console.log(xs));

async function mightFail(n: number): Promise<number> {
  if (n % 2 === 0) return n; else throw new Error("odd")
}

async function runSettled() {
  const results = await Promise.allSettled([mightFail(1), mightFail(2)]);
  for (const r of results) {
    if (r.status === "fulfilled") {
      // r: PromiseFulfilledResult<number>
      console.log("ok", r.value);
    } else {
      // r: PromiseRejectedResult
      console.warn("fail", r.reason);
    }
  }
}

runSettled();

function timeout<T>(ms: number, msg = "Timeout"): Promise<T> {
  return new Promise((_, reject) => setTimeout(() => reject(new Error(msg)), ms));
}

async function slow(): Promise<string> { return new Promise(res => setTimeout(() => res("done"), 100)); }

async function withTimeout() {
  const result = await Promise.race<Promise<string>>([
    slow(),
    timeout<string>(50, "Too slow"),
  ]);
  console.log(result);
}

withTimeout().catch(e => console.error("raced:", e.message));