Question 1

Callbacks, promises, and async/await — how do you choose?

Accepted Answer

Prefer async/await on promises for readability; wrap callback APIs with util.promisify; avoid callback hell. Keep error handling explicit with try/catch. Don't mix styles inconsistently in one module. Understand that async functions always return promises.

Question 2

What is the danger of unhandled promise rejections?

Accepted Answer

They can crash the process (depending on Node version/flags) or silently leave work incomplete. Always attach catch or await in try/catch. Use --unhandled-rejections=strict in CI. Log and alert on rejection events during migration.

Question 3

Promise.all vs Promise.allSettled vs Promise.race — when?

Accepted Answer

all fails fast; allSettled waits for all outcomes; race settles with the first. Use allSettled for fan-out where partial success matters. race for timeouts (careful with leaked work). all for required dependencies.

Question 4

How do you implement a timeout around an async operation?

Accepted Answer

AbortController + fetch signal, or Promise.race with a timer that aborts/cancels underlying work. Racing alone without cancelation leaves work running. Prefer abortable APIs. Clear timers to avoid leaks.

Question 5

Scenario: sequential awaits in a loop make an API slow. Fix?

Accepted Answer

Parallelize independent awaits with Promise.all / limited concurrency pools. Watch rate limits and DB connection pools. Use p-limit style concurrency. Preserve ordering only when required.

Question 6

Explain async context / AsyncLocalStorage use cases.

Accepted Answer

Propagate request IDs, tenants, and tracing context across async boundaries without explicit params. Powerful for logging/observability. Beware overhead and incorrect nesting. Don't store huge objects in ALS.

Async Programming Node.js Interview Questions

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