forEach With an Async Callback Debugging Lab

forEach With an Async CallbackEvents & ConcurrencyEasyPreparing workspaceAutosaved

00:00

Incident Dossier

forEach With an Async Callback

A nightly reconciler fans out per-account work via Array.prototype.forEach with an async callback. When one account's worker throws, the job still reports success because the rejection is on an unobserved promise.

Initial failing signalprocessAll resolves instead of rejecting on the failing itemExpected processAll rejects with the failing item id in the message · received processAll resolves to { processed: N } before the async work settles

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Look at the iteration helper in src/each.js.
Consider whether Array.prototype.forEach awaits the return value of its callback.
Replace the fan-out so the surrounding try/catch can observe the per-item rejections.

Focus Mode

Start

src/each.js

Likely area

src/each.js

Progressive hints

Hints reveal broad direction first, then narrow toward the suspect path without showing hidden tests or exact solution code.

TopicEvents & Concurrency

DifficultyEasy

Est. time12 min

Workspacecreating

Explorer

Preparing workspace files…

Evidence Map

Failing signal loaded from challenge API
Workspace files loaded from workspace API
Results rendered only after API run/submit

Autosaved

workspace

Outputread-onlyready$ workspace boot

Workspace booting...