Promises & async/await Interview Questions

A callback is a function I pass in to run later. Nested callbacks get messy, and errors are easy to swallow. A Promise is an object for a future value. I chain then, catch, finally. Promise.all fails if one fails. allSettled waits for every one. async/await is syntax on top of promises, not a second runtime. await pauses that async function and yields to the event loop. I use try/catch for errors. A mistake I still watch for is a floating promise I never await — the error vanishes. I would say I always return or await the promise.

all fails fast, allSettled waits for every one, race first settle, any first fulfill. I pick allSettled when I want errors too. I always return or await. No floating promises.

I would not Promise.all 1000 jobs. A pool of 3, start the next when one finishes. all() can stampede a backend. Abort signals if we must cancel.

A reject with no catch. Add catch or await try/catch. Empty catch is not a fix. Floating promises cause this. Node may crash in future versions.

No. forEach does not wait. Use for...of for series, or map plus all for parallel. I have reviewed this bug many times.

Follow release notes, RFCs or PEPs, official blogs, and reputable courses. Experiment in side projects when new Promises & async/await-related features ship so you can speak confidently about migration paths.

Table-driven tests, property-based tests for invariants, and benchmarks for hot paths. Mock external I/O but keep core Promises & async/await logic pure where possible so tests remain fast and reliable.

Use the official JavaScript docs for Promises & async/await, language or framework references, and reputable community guides. Bookmark release notes and migration guides when upgrading versions, since Promises & async/await behavior can change between releases.

Copying snippets without understanding why Promises & async/await works leads to fragile code. Beginners often skip error handling, tests, or edge cases. Slow down, trace execution step by step, and validate assumptions with small experiments.

Connect Promises & async/await to concrete types, concurrency primitives, or library modules. Cite a short example and when you would use it in production.

Describe exceptions or Result-style patterns as applicable to JavaScript. Propagate context, log carefully, and avoid masking failures in Promises & async/await.

Some Promises & async/await issues are caught by the compiler/linter; others appear with I/O or user input. That split drives tests and defensive coding.

Separate public API from internals, name clearly, document, and unit test. Follow community package layout idioms for JavaScript.

Avoid premature optimization but know traps: excess allocations, blocking I/O on hot paths, or O(n²) algorithms. Profile before optimizing Promises & async/await.

Follow release notes, RFCs/PEPs, and official blogs. Try new Promises & async/await-related features in side projects before production migrations.

Start with the problem Promises & async/await solves, show a minimal working example, and list the team conventions around it. Point them at official docs and one trusted internal example rather than random snippets.

Promises & async/await shows up often in production JavaScript work—misunderstanding it leads to bugs, performance issues, or security gaps. Interviewers want clear explanations plus practical judgment.

Describe scaffolding a feature, configuring defaults, or validating input where Promises & async/await is required. Call out what goes wrong if the team skips conventions around it.

Read the official overview, run a minimal sandbox, learn key terms and common errors, then expand with a small project. Hands-on practice beats memorizing Promises & async/await definitions.

Frame Promises & async/await as improving reliability, speed, security, or maintainability. Use a product outcome analogy, then note how JavaScript engineers apply Promises & async/await to deliver that outcome.

Official JavaScript documentation for Promises & async/await, language/framework references, and reputable guides. Track release notes because Promises & async/await behavior can change between versions.

Define clear ownership boundaries for Promises & async/await, failure domains, caching, and observability. Plan capacity, multi-region needs if relevant, and explicit trade-offs between consistency, latency, and cost.

Map the Promises & async/await attack surface (injection, broken auth, data exposure, DoS). Layer defenses—validation, rate limits, least privilege, encryption, and regular audits.

Cover correctness, failure modes, observability, and operational ownership for Promises & async/await in JavaScript. Scenario 1 should include a concrete metric and a rollback or mitigation plan.

Cover correctness, failure modes, observability, and operational ownership for Promises & async/await in JavaScript. Scenario 2 should include a concrete metric and a rollback or mitigation plan.