Fall back to ErrorEvent.message in special-pages error handlers by noisysocks · Pull Request #2714 · duckduckgo/content-scope-scripts

noisysocks · 2026-05-25T01:56:05Z

Asana Task/Github Issue: https://app.asana.com/1/137249556945/project/1207340338530322/task/1215001863923847

Description

The window.addEventListener('error', …) handlers in onboarding, new-tab, and history all read event.error?.message and fell through to 'unknown error' when event.error was null. That's the case for cross-origin script errors, some resource load failures, and throw undefined — ErrorEvent.message still has useful info (e.g. "Script error.") in those cases. The old code discarded it.

This produced the m_mac_onboarding_exception-reported spike on macOS 1.190.0 (message=[uncaught] unknown error, empty id) — the pixel landed in native but the JS side already lost everything diagnostic.

Fix: event.error?.message || event.message || 'unknown error'. Same change applied to all three special pages so they don't drift.

While there, simplify the unhandledrejection handler to event.reason?.message || String(event.reason) — same shape, and Promise.reject(undefined / null / 0) now report distinct messages (undefined, null, 0) instead of all collapsing to 'unknown rejection'.

Testing Steps

Open any of the three pages in a browser (swap new-tab for onboarding or history):
- https://rawcdn.githack.com/duckduckgo/content-scope-scripts/81f1dc2f56148e3e6b4269fe093247f9527aeaaf/build/integration/pages/new-tab/index.html
Open devtools console.

Paste this snippet and hit enter — it captures the native-bound notifications, fires every error/rejection shape we care about, and prints what the JS would send to native:

window.__playwright_01 = { mocks: { outgoing: [] }, subscriptions: new Map() };
const cases = [
  ['throw new Error',          () => setTimeout(() => { throw new Error('real error'); }, 0)],
  ['cross-origin shape (bug)', () => window.dispatchEvent(new ErrorEvent('error', { message: 'Script error.', filename: 'https://cdn.example/x.js', lineno: 42, colno: 7, error: null }))],
  ['truly empty error',        () => window.dispatchEvent(new ErrorEvent('error', { error: null }))],
  ['throw "raw string"',       () => setTimeout(() => { throw 'raw string'; }, 0)],
  ['Promise.reject(Error)',    () => setTimeout(() => Promise.reject(new Error('rejection')), 0)],
  ['Promise.reject(undefined)',() => setTimeout(() => Promise.reject(undefined), 0)],
  ['Promise.reject(null)',     () => setTimeout(() => Promise.reject(null), 0)],
  ['Promise.reject(0)',        () => setTimeout(() => Promise.reject(0), 0)],
];
(async () => {
  for (const [label, fn] of cases) {
    window.__playwright_01.mocks.outgoing.length = 0;
    try { fn(); } catch {}
    await new Promise(r => setTimeout(r, 200));
    const sent = window.__playwright_01.mocks.outgoing
      .map(c => typeof c.payload === 'string' ? c.payload : c.payload?.params?.message)
      .filter(m => typeof m === 'string' && (m.startsWith('[uncaught]') || m.startsWith('[unhandledrejection]')));
    console.log(label.padEnd(28), '→', sent.join(' | ') || '(nothing)');
  }
})();

You should see (the second line is the actual production bug being fixed):

throw new Error             → [uncaught] real error
cross-origin shape (bug)    → [uncaught] Script error.
truly empty error           → [uncaught] unknown error
throw "raw string"          → [uncaught] Uncaught raw string
Promise.reject(Error)       → [unhandledrejection] rejection
Promise.reject(undefined)   → [unhandledrejection] undefined
Promise.reject(null)        → [unhandledrejection] null
Promise.reject(0)           → [unhandledrejection] 0

Before this PR, the "cross-origin shape" line would have read [uncaught] unknown error, and the three falsy Promise.reject lines would all have read [unhandledrejection] unknown rejection.

Checklist

Please tick all that apply:

I have tested this change locally
I have tested this change locally in all supported browsers
This change will be visible to users
I have added automated tests that cover this change
I have ensured the change is gated by config
This change was covered by a ship review
This change was covered by a tech design
Any dependent config has been merged

Note

Low Risk
Telemetry-only message formatting in page bootstrap listeners; no auth, data, or user-facing behavior changes beyond clearer exception text sent to native.

Overview
Special-pages onboarding, new-tab, and history now build uncaught error reports from event.error?.message, then event.message, then a fallback—so cases like cross-origin ErrorEvent shapes (error: null, message still set) no longer collapse to [uncaught] unknown error.

Unhandled rejection reporting uses event.reason?.message || String(event.reason) so non-Error reasons (e.g. undefined, null, 0) send distinct native messages instead of a generic unknown string.

Onboarding integration tests cover the ErrorEvent.message fallback and those rejection shapes.

^{Reviewed by Cursor Bugbot for commit ca9c960. Bugbot is set up for automated code reviews on this repo. Configure here.}

Cross-origin script errors fire with event.error=null but useful info in event.message. The old handler discarded that and reported '[uncaught] unknown error', which is what produced the m_mac_onboarding_exception-reported spike on macOS 1.190.0. Also simplify the rejection handler so falsy reasons (undefined, null, 0) report distinct messages instead of all bucketing to 'unknown'. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

github-actions · 2026-05-25T01:56:31Z

Build Branch


Branch	`pr-releases/randerson/special-pages-error-handler-fallback`
Commit	`0870971e5b`
Updated	May 25, 2026 at 9:44:55 AM UTC

Static preview entry points

Docs: docs/index.html
Static pages: build/integration/pages/index.html
Integration pages: injected/integration-test/test-pages/index.html

QR codes (mobile preview)

Entry point	QR code
Docs
Static pages
Integration pages

Integration commands

npm (Android / Extension):

npm i github:duckduckgo/content-scope-scripts#pr-releases/randerson/special-pages-error-handler-fallback

Swift Package Manager (Apple):

.package(url: "https://github.com/duckduckgo/content-scope-scripts.git", branch: "pr-releases/randerson/special-pages-error-handler-fallback")

git submodule (Windows):

git -C submodules/content-scope-scripts fetch origin pr-releases/randerson/special-pages-error-handler-fallback
git -C submodules/content-scope-scripts checkout origin/pr-releases/randerson/special-pages-error-handler-fallback

Pin to exact commit

npm (Android / Extension):

npm i github:duckduckgo/content-scope-scripts#0870971e5b01e61cbd2dd2c569b82d1cad85b89a

Swift Package Manager (Apple):

.package(url: "https://github.com/duckduckgo/content-scope-scripts.git", revision: "0870971e5b01e61cbd2dd2c569b82d1cad85b89a")

git submodule (Windows):

git -C submodules/content-scope-scripts fetch origin pr-releases/randerson/special-pages-error-handler-fallback
git -C submodules/content-scope-scripts checkout 0870971e5b01e61cbd2dd2c569b82d1cad85b89a

github-actions · 2026-05-25T01:57:15Z

[Beta] Generated file diff

Time updated: Mon, 25 May 2026 09:45:43 GMT

Apple

    - apple/pages/history/dist/index.js

apple/pages/new-tab/dist/index.js
apple/pages/onboarding/dist/index.js

File has changed

Integration

    - integration/pages/history/dist/index.js

integration/pages/new-tab/dist/index.js
integration/pages/onboarding/dist/index.js

File has changed

Windows

    - windows/pages/history/dist/index.js

windows/pages/new-tab/dist/index.js
windows/pages/onboarding/dist/index.js

File has changed

cursor

Stale comment

Web Compatibility Assessment

No web-compat findings.

special-pages/pages/history/src/index.js:86-93, special-pages/pages/new-tab/src/index.js:113-120, special-pages/pages/onboarding/app/index.js:40-47 - info: the changed listeners only affect diagnostic reporting for special pages. They do not wrap/shim browser APIs, alter prototypes/descriptors, mutate the DOM, or change injected page-world behavior.

Same ranges - info: existing integration tests cover throw new Error(...) and Promise.reject(new Error(...)); the new ErrorEvent.message and primitive rejection fallback paths are manually verified but not covered by automated tests.

Security Assessment

No security findings.

Same ranges - info: the outgoing payload remains a literal reportInitException message; there is no nativeData spreading, message bridge change, origin validation change, new network request, postMessage, or privileged data exposure. This is special-page app code, not hostile page-world injected code.

Risk Level

Low Risk - limited to three special-page global error/rejection diagnostic handlers, with no injected runtime, wrapper utility, captured-global, or messaging transport changes.

Recommendations

Non-blocking: add explicit integration coverage for new ErrorEvent('error', { message: 'Script error.', error: null }) and primitive/nullish rejection reasons (undefined, null, 0) in the existing global error listener suites so the new fallback behavior does not regress.

_{Sent by Cursor Automation: Web compat and sec}

shakyShane

If it's provable in a console snippet, could you add a playwright test to at least one of these?

Dismissing stale approval — new commits pushed, awaiting Cursor re-review.

cursor

Stale comment

Web Compatibility Assessment

No web-compat findings.

special-pages/pages/history/src/index.js lines 86-93, special-pages/pages/new-tab/src/index.js lines 113-120, special-pages/pages/onboarding/app/index.js lines 40-47 - info: the changed global error/rejection listeners only affect diagnostic reporting in special pages. They do not wrap or shim browser APIs, alter prototypes/descriptors, mutate page DOM, or change injected page-world behavior.

special-pages/pages/onboarding/integration-tests/onboarding.v4.spec.js lines 855-891 - info: the previously missing fallback coverage is now present for cross-origin-style ErrorEvent objects with error: null and for primitive/nullish rejection reasons.

Security Assessment

No security findings.

Same handler ranges - info: the outgoing reportInitException payload remains a literal message object/string and does not spread untrusted objects, include nativeData, add postMessage, change origin validation, or touch the message bridge. The template-literal callsites preserve the message: string contract before data crosses the special-page native messaging boundary.

Risk Level

Low Risk - limited to special-page diagnostic fallback logic and targeted Playwright coverage, with no injected runtime, wrapper utility, captured-global, or messaging transport changes.

Recommendations

No blocking recommendations.

Validation: npm run test-int -- pages/onboarding/integration-tests/onboarding.v4.spec.js --grep "global error listeners" --reporter list passed (10 passed).

_{Sent by Cursor Automation: Web compat and sec}

cursor

Web Compatibility Assessment

No web-compat findings.

special-pages/pages/history/src/index.js:86-93, special-pages/pages/new-tab/src/index.js:113-120, special-pages/pages/onboarding/app/index.js:40-47 - info: the changed listeners only affect diagnostic error reporting in special pages. They do not wrap/shim browser APIs, alter prototypes/descriptors, mutate DOM structure, or affect injected page-world behavior.
special-pages/pages/onboarding/integration-tests/onboarding.v4.spec.js:855-889 - info: the synchronized update adds automated coverage for the previously noted ErrorEvent.message fallback and primitive/nullish rejection reasons.

Security Assessment

No security findings.

Same handler ranges - info: outgoing messages remain literal reportInitException payloads with only a stringified message; there is no nativeData spreading, message bridge change, origin-validation relaxation, new network request, postMessage, or privileged data exposure.

Risk Level

Low Risk - limited to special-page diagnostic handlers and targeted onboarding integration tests, with no injected runtime, wrapper utility, captured-global, or messaging transport changes.

Recommendations

No blocking recommendations. Targeted validation passed: npm run test-int -- --grep "global error listeners" --reporter list from special-pages/ (16 passed).

_{Sent by Cursor Automation: Web compat and sec}

Covers the cross-origin ErrorEvent shape (error=null) that produced the production pixel, and the primitive/nullish rejection reasons (undefined, null, 0) that previously all bucketed to 'unknown rejection'. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

github-actions · 2026-05-25T09:44:37Z

⚠️ Cursor review was not successful.

This PR requires a manual review and approval from a member of one of the following teams:

@duckduckgo/content-scope-scripts-owners
@duckduckgo/apple-devs
@duckduckgo/android-devs
@duckduckgo/team-windows-development
@duckduckgo/extension-owners
@duckduckgo/config-aor
@duckduckgo/breakage-aor
@duckduckgo/breakage

github-actions Bot added the semver-patch Bug fix / internal — no release needed label May 25, 2026

cursor Bot reviewed May 25, 2026

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daxtheduck previously approved these changes May 25, 2026

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noisysocks requested a review from shakyShane May 25, 2026 02:01

shakyShane requested changes May 25, 2026

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daxtheduck previously approved these changes May 25, 2026

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noisysocks force-pushed the randerson/special-pages-error-handler-fallback branch from d208bc7 to 751431f Compare May 25, 2026 09:41

cursor Bot reviewed May 25, 2026

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noisysocks force-pushed the randerson/special-pages-error-handler-fallback branch from 751431f to ca9c960 Compare May 25, 2026 09:44

daxtheduck approved these changes May 25, 2026

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noisysocks requested a review from shakyShane May 25, 2026 09:50

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Fall back to ErrorEvent.message in special-pages error handlers#2714

Fall back to ErrorEvent.message in special-pages error handlers#2714
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Testing Steps

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