Debugging scenarioMedium~10 minJavaScript Language & Async Semantics / 6 of 9

Interview question

A rejected promise bypasses the error handling you expected. How do errors propagate through promises and async/await?

Traces synchronous throws and promise rejections through chains, awaits, missing returns, and detached work.

1Say itAnswer out loud first

2CompareCompare with Core answer

3RefineRefine with Stronger and Advanced

TL;DR

An async function always returns a promise. Throwing inside it rejects that promise, and awaiting a rejected promise throws at the await point. A .then handler that throws also returns a rejected promise. I trace which promise is returned or awaited; if code starts asynchronous work without either, an outer try/catch may finish before the rejection occurs.

Full answer below

Practice focus

Whether the candidate can follow the actual promise chain and place handling at an intentional ownership boundary.

Answer first

Answer path

Core answer first, then checkpoints toward a stronger answer.

Start
Core answer
Start here. This is the direct spoken answer to practice first.
Overview
A try block handles an awaited rejection inside it. It cannot catch a promise that was started and detached without being awaited or returned.
An async function always returns a promise. Throwing inside it rejects that promise, and awaiting a rejected promise throws at the await point. A .then handler that throws also returns a rejected promise. I trace which promise is returned or awaited; if code starts asynchronous work without either, an outer try/catch may finish before the rejection occurs.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
A common bug is forgetting return in a promise callback or forgetting await inside a try. The caller then sees early success while the detached operation later rejects. I fix the ownership first: return or await work that belongs to the request, and attach an explicit terminal handler only for intentionally independent work. I do not add scattered catches that log and silently convert failure into success.
Finish
Advanced answer
Optional deeper angle for production judgment and nuance.
At a UI boundary I classify cancellation, expected domain rejection, dependency failure, and programmer error differently. A catch should recover, translate, or rethrow with useful context; it should not erase the original cause. For concurrent work, I choose a combinator whose rejection semantics match the product requirement and ensure every started operation is observed, even when another result fails first. In production, I instrument unhandled rejections with operation and request context while excluding sensitive payloads.

Review signals

Use these to catch weak phrasing, shallow reasoning, and risky claims.

Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Assuming try/catch catches any later promise rejection automatically.
Catching an error, logging it, and returning implicit success.
Forgetting to return a nested promise chain.
Treating user cancellation as an unexpected application failure.

Red flagsCandidateRed flagsSignals that an interviewer may treat as risky.Open details

Details

Detached promises have no owner or terminal error handling.
The proposed fix adds await everywhere without considering concurrency.
Error translation loses the original cause and operation context.

Follow-up prompts

Quick interviewer prompts inside this drill.

Follow-up questionsCandidateFollow-up questionsLikely next questions after the main answer.Open details

Details

Treat these as the next interviewer turn. Answer one out loud, then save the gap in your practice notes.

What happens when a .then handler throws?
Why can a missing return cause early completion?
How would you handle intentionally fire-and-forget work?

Continue the section

Next in JavaScript Language & Async Semantics: Choose a Promise combinator

Step 7 of 9

When would you use Promise.all, allSettled, race, or any?

Practice route

Read core answer Review checklist Follow-up prompts Track progress

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Drill details

Human editorial direction

Aporeon is shaped by Aleksandar Tomovski, a software developer with experience on both sides of technical interviews. Content is reviewed for accuracy, natural spoken delivery, useful depth, and honest trade-offs.

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