JavaScript Async Await Interview Questions 2026: 26 Q&A

Last Updated: June 2026 | Level: Freshers to Mid-Level | Read Time: ~16 min

Asynchronous JavaScript separates juniors from mid-level developers in interviews. Candidates report that the event loop, promise combinators, and async error handling are guaranteed for frontend and Node roles. This guide covers 26 async questions with full answers, runnable code, and predict-the-output traps. Behaviour reflects the official MDN documentation; confirm any event-loop nuance on MDN, since ordering questions hinge on a single rule.

Pair this with JavaScript Interview Questions for Freshers 2026 and JavaScript Output Questions 2026.

Table of Contents

1. Promises Basics (Q1 to Q9)
2. async await (Q10 to Q17)
3. Event Loop and Ordering (Q18 to Q22)
4. Error Handling and Combinators (Q23 to Q26)
5. Predict the Output
6. Quick Revision Table
7. Frequently Asked Questions

Promises Basics

Q1. What is a promise? Easy

Q2. What are the states of a promise? Easy

Q3. What is the difference between a callback and a promise? Medium

Q4. What does Promise.resolve do? Easy

Q5. How does promise chaining work? Medium

fetchUser()
  .then(u => fetchOrders(u.id))
  .then(orders => render(orders))
  .catch(err => showError(err));

Q6. What does returning a value vs a promise from then do? Medium

Q7. What is promise flattening? Hard

Q8. What does .finally do? Easy

Q9. Can you cancel a promise? Hard

async await

Q10. What is async await? Easy

Q11. What does an async function return? Medium

Q12. What does await actually do? Medium

Q13. How do you run async operations in parallel? Medium

const [a, b] = await Promise.all([fetchA(), fetchB()]); // parallel

Q14. What is the cost of sequential awaits? Medium

Q15. Can you use await at the top level? Medium

Q16. What happens if you forget to await a promise? Hard

Q17. How do you await inside a loop correctly? Hard

Event Loop and Ordering

Q18. What is the event loop? Medium

Q19. What is the difference between microtasks and macrotasks? Hard

Q20. Why does a promise callback run before setTimeout(0)? Hard

Q21. What is queueMicrotask? Medium

Q22. Does await block the thread? Hard

Error Handling and Combinators

Q23. How do you handle errors with async await? Medium

async function load() {
  try { return await fetchData(); }
  catch (e) { return fallback; }
}

Q24. What is the difference between Promise.all and Promise.allSettled? Hard

Q25. What do Promise.race and Promise.any do? Hard

Q26. Why can a synchronous try/catch miss a promise rejection? Hard

Predict the Output

Snippet 1

console.log("1");
setTimeout(() => console.log("2"), 0);
Promise.resolve().then(() => console.log("3"));
console.log("4");

Output:

1
4
3
2

Why: Sync first (1, 4), then microtask (3), then macrotask (2).

Snippet 2

async function f() {
  console.log("a");
  await Promise.resolve();
  console.log("b");
}
console.log("start");
f();
console.log("end");

Output:

start
a
end
b

Why: Code up to the await runs synchronously; the continuation is a microtask after the current stack clears.

Snippet 3

Promise.all([
  Promise.resolve(1),
  Promise.reject("x"),
  Promise.resolve(3)
]).then(console.log).catch(e => console.log("caught", e));

Output:

caught x

Why: Promise.all rejects on the first rejection, so the catch fires with "x" and the resolved values are discarded.

Quick Revision Table

Related Articles

• JavaScript Interview Questions for Freshers 2026, the master set
• JavaScript Output Questions 2026, event-loop traps
• JavaScript Closures Interview Questions 2026, closures in depth
• JavaScript Coding Questions With Solutions 2026, solved problems

Confirm any event-loop or promise detail on the official MDN documentation before your interview. This guide reflects candidate-reported patterns and public preparation resources as of June 2026.