#7 most askedVery commonMediumAsync & promises

Promises vs async/await

🏢 Asked in real interviews

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What is a Promise, and how does async/await relate to it? How do you handle errors with each?

🎤 Answer it out loud, then check yourself

Say your answer as if the interviewer is listening (30–90 seconds). Then reveal what a strong answer covers and tick what you said.

const wait = (ms, v) => new Promise((r) => setTimeout(() => r(v), ms));

async function sequential() {
  const a = await wait(30, "a");
  const b = await wait(30, "b");
  return a + b;
}
async function parallel() {
  const [a, b] = await Promise.all([wait(30, "a"), wait(30, "b")]);
  return a + b;
}

let t = Date.now();
await sequential();
console.log("sequential ms ≈", Math.round((Date.now() - t) / 10) * 10);
t = Date.now();
await parallel();
console.log("parallel ms ≈", Math.round((Date.now() - t) / 10) * 10);

Answer out loud first, then compare.

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