Prevent LHN crash on undefined item and out-of-range web scroll index by wildan-m · Pull Request #91488 · Expensify/App

wildan-m · 2026-05-23T02:24:23Z

Explanation of Change

On web, the app could crash with a TypeError while rendering the left-hand navigation list. The list's row renderer read a report's ID as its very first step, without checking that the row actually existed.

This was reachable because, on web only, the list restores a previously saved scroll position when it mounts. That position is never re-validated against the current list, which grows and shrinks constantly (reports archived or deleted, filters applied, priority mode toggled, accounts switched). Once the list had shrunk below the saved position, the list component looked up a row that no longer existed and passed an empty row to the renderer, which crashed reading the report's ID. On native the saved position is not used, which is why the crash was web-only.

This fixes both layers. The row renderer now returns an empty row when it has no data, instead of reading the report's ID — consistent with the rest of that callback, which already treats the row as possibly missing. And the saved web scroll position is now used only when it still falls within the current list; otherwise the list starts at the top. The second change removes the actual trigger, and the first guarantees the crash cannot happen regardless of how an empty row arrives.

The only behavioral change is in the out-of-range case: when the saved web scroll position no longer fits the list, the navigation starts at the top instead of crashing. When the saved position is still valid, behavior is unchanged.

Fixed Issues

$ #91226
PROPOSAL: #91226 (comment)

Tests

This is a non-deterministic crash reported through Sentry — the issue lists reproduction as "Unknown" (it happens during a concurrent-rendering recovery race when the left-hand navigation (LHN) list shrinks below a previously saved web scroll index, so it can't be triggered by normal use). The patch below forces the underlying out-of-range-index condition deterministically, on any account — no need for many chats.

Deterministic reproduction (any account size)

The crash needs the saved web scroll index to point past the end of the current list. You can't naturally save a high index on a short list, so temporarily force getScrollIndex to return an out-of-range value. This file is not modified by this PR, so the exact same patch applies to both main and this branch.

In src/components/ScrollOffsetContextProvider.tsx, replace the body of getScrollIndex:

-    const getScrollIndex: ScrollOffsetContextValue['getScrollIndex'] = useCallback((route) => {
-        if (!scrollOffsetsRef.current) {
-            return;
-        }
-        return scrollOffsetsRef.current[getKey(route)];
-    }, []);
+    const getScrollIndex: ScrollOffsetContextValue['getScrollIndex'] = useCallback(() => {
+        // TEMP: force an out-of-range saved scroll index to reproduce the LHN crash
+        return 9999;
+    }, []);

On main with the patch applied: open the app on web and sign in. The LHN crashes into the "Uh-oh, something went wrong!" error boundary on load. The JS console shows crash caught by error boundary - index out of bounds, not enough layouts with a component stack through LHNOptionsList. (This is the deterministic, mount-time sibling of the production t.reportID race — same root cause: an out-of-range index reaching FlashList.)
On this PR branch with the same patch applied: open the app on web and sign in. The LHN renders normally and starts at the top — no crash, clean console. The fix clamps the out-of-range index to "start at the top."
Remove the patch when done.

Regression checks (real fix in place, no patch)

On web, scroll the LHN up and down and open/switch between several chats; confirm everything renders with no crash.
Run the unit tests: npx jest tests/ui/components/LHNOptionsListTest.tsx tests/ui/components/LHNOptionsListRenderItemTest.tsx. They cover the scroll-index validation (in range, past the end, negative, empty list, no saved index) and the guard that returns an empty row for a missing item.

Verify that no errors appear in the JS console

Offline tests

No offline-specific behavior changes. The LHN renders the same offline; the guards only change what happens when the list shrinks (which can also occur offline during an optimistic delete) — preventing the crash and starting at the top when the saved scroll position is out of range.

QA Steps

This crash can't be reproduced on demand — it's a non-deterministic race, and the deterministic repro in the Tests section needs a local code patch that doesn't apply on staging. QA can confirm there's no regression in the left-hand navigation (LHN). This works on any account and does not depend on how many chats it has:

On web (staging), sign in to any account.
Confirm the LHN (the list of chats on the left) loads and renders correctly.
Scroll the LHN up and down, then open and switch between a few chats; confirm the correct chat opens each time and nothing crashes.

Verify that no errors appear in the JS console

PR Author Checklist

Screenshots/Videos

Android: Native

Kapture.2026-05-23.at.13.25.23.mp4

Android: mWeb Chrome

Kapture.2026-05-23.at.13.29.33.mp4

iOS: Native

Kapture.2026-05-23.at.13.17.23.mp4

iOS: mWeb Safari

Kapture.2026-05-23.at.13.20.53.mp4

MacOS: Chrome / Safari

Kapture.2026-05-23.at.11.47.49_compressed.mp4

…index Guard renderItem against a transient undefined item instead of reading item.reportID directly, and only restore the saved web scroll index when it is still within the current data range so FlashList is never asked to render a non-existent row.

…tions-list-undefined-item

Move the in-range scroll-index validation into a small pure helper so it can be unit-tested directly, and add tests covering the index validation (in-range, out-of-range, negative, empty list, no saved index) and the renderItem guard returning null for an undefined item.

codecov · 2026-05-23T02:31:54Z

Codecov Report

✅ Changes either increased or maintained existing code coverage, great job!

Files with missing lines	Coverage Δ
src/components/LHNOptionsList/LHNOptionsList.tsx	`81.25% <100.00%> (+1.93%)`	⬆️
... and 11 files with indirect coverage changes

melvin-bot · 2026-05-23T06:34:44Z

@gijoe0295 Please copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]

gijoe0295 · 2026-05-25T16:35:22Z

Remove this test. This is niche

gijoe0295 · 2026-05-25T16:35:31Z

gijoe0295 · 2026-05-25T16:36:11Z

+            // FlashList can momentarily hand us an undefined item while the list shrinks before the
+            // recycler rebuilds. Bail out for that transient slot instead of reading item.reportID and
+            // crashing. The rest of this callback already guards item with optional chaining.


Suggested change

// FlashList can momentarily hand us an undefined item while the list shrinks before the

// recycler rebuilds. Bail out for that transient slot instead of reading item.reportID and

// crashing. The rest of this callback already guards item with optional chaining.

gijoe0295 · 2026-05-25T16:36:34Z

            const itemOneTransactionThreadReport = reports?.[`${ONYXKEYS.COLLECTION.REPORT}${itemReportAttributes?.oneTransactionThreadReportID}`];

            let invoiceReceiverPolicyID = '-1';
            if (item?.invoiceReceiver && 'policyID' in item.invoiceReceiver) {


Suggested change

if (item.invoiceReceiver && 'policyID' in item.invoiceReceiver) {

gijoe0295 · 2026-05-25T16:36:41Z

                invoiceReceiverPolicyID = itemParentReport.invoiceReceiver.policyID;
            }
            const itemInvoiceReceiverPolicy = policy?.[`${ONYXKEYS.COLLECTION.POLICY}${invoiceReceiverPolicyID}`];
            const itemPolicy = policy?.[`${ONYXKEYS.COLLECTION.POLICY}${item?.policyID}`];


Suggested change

const itemPolicy = policy?.[`${ONYXKEYS.COLLECTION.POLICY}${item.policyID}`];

gijoe0295 · 2026-05-25T17:57:16Z

        });
    }, [getScrollOffset, route]);

+    const initialScrollIndex = getInitialScrollIndex(isWeb ? getScrollIndex(route) : undefined, data.length);


Suggested change

const initialScrollIndex = getInitialScrollIndex(isWeb ? getScrollIndex(route) : undefined, data.length);

const savedScrollIndex = getScrollIndex(route);

const initialScrollIndex = isWeb && savedScrollIndex && savedScrollIndex >= 0 && savedScrollIndex < data.length ? savedScrollIndex : undefined;

gijoe0295 · 2026-05-25T17:57:46Z

+/**
+ * Restores the saved web scroll index only when it is still in range. The list length changes
+ * constantly (archived/deleted reports, filters, priority mode, account switches), so a saved index
+ * can point past the end. Returning undefined makes FlashList start at the top instead of looking up
+ * data[index] === undefined and handing renderItem a missing item.
+ */
+function getInitialScrollIndex(savedScrollIndex: number | undefined, dataLength: number): number | undefined {
+    if (savedScrollIndex === undefined || savedScrollIndex < 0 || savedScrollIndex >= dataLength) {
+        return undefined;
+    }
+    return savedScrollIndex;
+}
+


Suggested change

/**

* Restores the saved web scroll index only when it is still in range. The list length changes

* constantly (archived/deleted reports, filters, priority mode, account switches), so a saved index

* can point past the end. Returning undefined makes FlashList start at the top instead of looking up

* data[index] === undefined and handing renderItem a missing item.

*/

function getInitialScrollIndex(savedScrollIndex: number | undefined, dataLength: number): number | undefined {

if (savedScrollIndex === undefined || savedScrollIndex < 0 || savedScrollIndex >= dataLength) {

return undefined;

}

return savedScrollIndex;

}

gijoe0295 · 2026-05-25T17:58:19Z

Reviewer Checklist

I have verified the author checklist is complete (all boxes are checked off).
I verified the correct issue is linked in the ### Fixed Issues section above
I verified testing steps are clear and they cover the changes made in this PR
- I verified the steps for local testing are in the Tests section
- I verified the steps for Staging and/or Production testing are in the QA steps section
- I verified the steps cover any possible failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
- I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
I checked that screenshots or videos are included for tests on all platforms
I included screenshots or videos for tests on all platforms
I verified that the composer does not automatically focus or open the keyboard on mobile unless explicitly intended. This includes checking that returning the app from the background does not unexpectedly open the keyboard.
I verified tests pass on all platforms & I tested again on:
- Android: HybridApp
- Android: mWeb Chrome
- iOS: HybridApp
- iOS: mWeb Safari
- MacOS: Chrome / Safari
If there are any errors in the console that are unrelated to this PR, I either fixed them (preferred) or linked to where I reported them in Slack
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- I verified that any callback methods that were added or modified are named for what the method does and never what callback they handle (i.e. toggleReport and not onIconClick).
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- I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
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- I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
- I verified proper file naming conventions were followed for any new files or renamed files. All non-platform specific files are named after what they export and are not named "index.js". All platform-specific files are named for the platform the code supports as outlined in the README.
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Screenshots/Videos

Android: HybridApp

Screen.Recording.2026-05-26.at.01.07.18.mov

Android: mWeb Chrome

Screen.Recording.2026-05-26.at.01.11.47.mov

iOS: HybridApp

Screen.Recording.2026-05-26.at.01.14.16.mov

iOS: mWeb Safari

MacOS: Chrome / Safari

Screen.Recording.2026-05-26.at.01.02.06.mov

gijoe0295 · 2026-05-25T18:01:54Z

Let's remove the redundant wordy explanation from PR body. The Explanation of Change section can be simplified. Offline tests can just be None. Remove the explanation on top of QA tests: "This crash can't be reproduced on demand ...". Same for Tests section.

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wildan-m added 4 commits May 21, 2026 15:40

Merge remote-tracking branch 'upstream/main' into wildan/91226-lhn-op…

d9d219f

…tions-list-undefined-item

Trim LHNOptionsList comments to focus on the why

2670240

melvin-bot Bot assigned wildan-m May 23, 2026

wildan-m marked this pull request as ready for review May 23, 2026 06:34

wildan-m requested review from a team as code owners May 23, 2026 06:34

melvin-bot Bot requested review from gijoe0295 and removed request for a team May 23, 2026 06:34

wildan-m mentioned this pull request May 23, 2026

[$250] [Sentry: APP-AZ6] TypeError: undefined is not an object (evaluating 't.reportID') in LHNOptionsList renderItem #91226

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Prevent LHN crash on undefined item and out-of-range web scroll index#91488

Prevent LHN crash on undefined item and out-of-range web scroll index#91488
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	// FlashList can momentarily hand us an undefined item while the list shrinks before the
	// recycler rebuilds. Bail out for that transient slot instead of reading item.reportID and
	// crashing. The rest of this callback already guards item with optional chaining.


	if (item.invoiceReceiver && 'policyID' in item.invoiceReceiver) {


	const itemPolicy = policy?.[`${ONYXKEYS.COLLECTION.POLICY}${item.policyID}`];

	const initialScrollIndex = getInitialScrollIndex(isWeb ? getScrollIndex(route) : undefined, data.length);
	const savedScrollIndex = getScrollIndex(route);
	const initialScrollIndex = isWeb && savedScrollIndex && savedScrollIndex >= 0 && savedScrollIndex < data.length ? savedScrollIndex : undefined;

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Explanation of Change

Fixed Issues

Tests

Deterministic reproduction (any account size)

Regression checks (real fix in place, no patch)

Offline tests

QA Steps

PR Author Checklist

Screenshots/Videos

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