Debugging scenarioHard~15 minBrowser Rendering, CSS & Storage / 5 of 5

Interview question

Some users receive an old HTML shell with new assets, or a new shell that requests deleted chunks after deployment. How would you diagnose and prevent it?

Diagnoses incompatible cached HTML and immutable assets across CDN, browser, service-worker, and rollout boundaries.

1Say itAnswer out loud first

2CompareCompare with Core answer

3RefineRefine with Stronger and Advanced

TL;DR

I capture the failing document URL, requested chunk URL, response status, cache headers, age, CDN result, service-worker state, and deployment version. Hashed assets can be cached for a long time because their URLs change with content, but HTML should revalidate frequently. I keep old hashed assets available long enough that cached HTML can still load them.

Full answer below

Practice focus

Production judgment about cache policy, atomic compatibility, evidence, rollback, and user recovery.

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
The failure is a version-skew problem. The investigation must identify which layer served each artifact and which versions are compatible.
I capture the failing document URL, requested chunk URL, response status, cache headers, age, CDN result, service-worker state, and deployment version. Hashed assets can be cached for a long time because their URLs change with content, but HTML should revalidate frequently. I keep old hashed assets available long enough that cached HTML can still load them.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
I reproduce with the affected browser and CDN region, then compare the HTML's asset manifest with what the origin and edge currently serve. A service worker may also return an older shell, so I inspect its cache and update lifecycle. The deployment should publish new assets before exposing new HTML and avoid deleting the previous generation immediately. A chunk-load failure can offer one controlled refresh rather than trapping the user in a reload loop.
Finish
Advanced answer
Optional deeper angle for production judgment and nuance.
I design releases for bounded version skew: immutable content-addressed assets, short-lived or revalidated entry documents, compatible API changes, atomic manifest promotion, retention of recent assets, and a tested rollback path. Telemetry includes build identifiers for HTML and runtime errors so failures can be sliced by version and edge. Service-worker activation and cache cleanup are coordinated so one tab does not invalidate resources another active tab still needs. A release smoke test loads the public entry point through the CDN and verifies that every referenced asset resolves before old artifacts are retired.

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

Purging every cache repeatedly without identifying the stale layer.
Caching HTML as immutable alongside hashed assets.
Deleting the previous asset generation as soon as deployment finishes.
Fixing chunk failures with an unlimited reload loop.

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

Details

The team cannot correlate an error with an application build.
Deployment order exposes HTML before its assets are globally available.
Rollback cannot restore a compatible shell and asset set.

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.

Which resources should be immutable?
How would a service worker create version skew?
What should the UI do after a chunk-load failure?

Continue practice

Move to the linked follow-up, next path step, prerequisite, or deeper variant.

2 linked

Try a variant

Answer a similar question in a different context.

API Cache-ControlContrast entry-document and asset caching with API response caching.ETag conditional GETUse conditional revalidation for resources that must not remain immutable.

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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