perf(search): cache onFocus handlers per index to stop row re-renders

[TMisiukiewicz]

Explanation of Change

Every visible Search row was re-rendering on any list render because its onFocus prop was a brand-new function each time. The handler captures the row's index, so it can't be memoized — a fresh closure is allocated per row, per render.

Added useStableIndexedHandler that caches one handler per index in a ref. Same row → same onFocus reference across renders.

Considered alternative solutions:

• Lift binding into each row — would require change in ~10 files, couples rows to list position (index)
• Move focus into a context — more architectural change, every list item component would require to be tied to the context

Fixed Issues

$ #90456
PROPOSAL:

Tests

1. Open Search.
2. Use Arrow Down/Up
3. Verify the focus goes with every press
4. Press Enter on a focused row
5. Verify the report opened

• Verify that no errors appear in the JS console

Offline tests

Same as Tests — focus tracking is local and works offline.

QA Steps

Same as Tests.

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
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  • I added steps to cover 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 tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
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Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

Screen.Recording.2026-05-13.at.10.44.47.mov

[codecov]

Codecov Report

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

Files with missing lines	Coverage Δ
src/hooks/useStableIndexedHandler.ts	100.00% <100.00%> (ø)
...ponents/Search/SearchList/BaseSearchList/index.tsx	0.00% <0.00%> (ø)
... and 136 files with indirect coverage changes

[melvin-bot]

@situchan 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]

[situchan]

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
  • MacOS: Desktop
• 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
• I verified there are no new alerts related to the canBeMissing param for useOnyx
• I verified proper code patterns were followed (see Reviewing the code)
  • 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).
  • I verified that comments were added to code that is not self explanatory
  • 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.
  • I verified any copy / text shown in the product is localized by adding it to src/languages/* files and using the translation method
  • I verified all numbers, amounts, dates and phone numbers shown in the product are using the localization methods
  • 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.
  • I verified the JSDocs style guidelines (in STYLE.md) were followed
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I verified that this PR follows the guidelines as stated in the Review Guidelines
• I verified other components that can be impacted by these changes have been tested, and I retested again (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar have been tested & I retested again)
• I verified all code is DRY (the PR doesn't include any logic written more than once, with the exception of tests)
• I verified any variables that can be defined as constants (ie. in CONST.ts or at the top of the file that uses the constant) are defined as such
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• If any new file was added I verified that:
  • The file has a description of what it does and/or why is needed at the top of the file if the code is not self explanatory
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  • A similar style doesn't already exist
  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG)
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• If the PR modifies a component related to any of the existing Storybook stories, I tested and verified all stories for that component are still working as expected.
• If the PR modifies a component or page that can be accessed by a direct deeplink, I verified that the code functions as expected when the deeplink is used - from a logged in and logged out account.
• If the PR modifies the UI (e.g. new buttons, new UI components, changing the padding/spacing/sizing, moving components, etc) or modifies the form input styles:
  • I verified that all the inputs inside a form are aligned with each other.
  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• If a new page is added, I verified it's using the ScrollView component to make it scrollable when more elements are added to the page.
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• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.
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Screenshots/Videos

Android: HybridApp

Android: mWeb Chrome

iOS: HybridApp

ios.mov

iOS: mWeb Safari

msafari.mov

MacOS: Chrome / Safari

web.mov

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 7a429b9c2c

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[MelvinBot]

PR Review

Overall: Good approach — caching per-index handlers to avoid fresh closures on every render is a valid optimization for virtualized lists. A few items to address:

1. Stale cache when handler changes (bug)

The cache in useStableIndexedHandler.ts:19-30 is never cleared when handler changes. When handler changes:

1. useCallback returns a new factory (correct — [handler] dep)
2. But cacheRef.current still holds old entries closing over the old handler
3. cache.get(index) returns the stale binding

The docstring says "caller must pass a stable handler," but the hook should still be defensive. If handler changes, the cache should be cleared:

return useCallback(
    (index: number) => {
        const cache = cacheRef.current;
        const cached = cache.get(index);
        if (cached) {
            return cached;
        }
        const bound = (...args: Args) => handler(index, ...args);
        cache.set(index, bound);
        return bound;
    },
    // When handler changes, clear the cache so stale closures aren't returned
    // eslint-disable-next-line react-compiler/react-compiler, react-hooks/exhaustive-deps
    [handler, cacheRef.current = handler !== prevHandlerRef.current ? new Map() : cacheRef.current],
);

Or more simply, add an effect:

const prevHandlerRef = useRef(handler);
if (prevHandlerRef.current !== handler) {
    cacheRef.current = new Map();
    prevHandlerRef.current = handler;
}

This prevents a class of subtle bugs if the hook is reused elsewhere with a less-stable handler.

2. Re: situchan's React Compiler question

The useCallback in the hook (line 21) is required even with React Compiler. The compiler memoizes the factory function, but cannot reason about the ref-based cache pattern — specifically, it doesn't know that returning a cached closure from a Map inside a ref needs to produce a stable reference. The explicit useCallback with [handler] dependency is what guarantees the factory identity stays the same across renders when handler is stable.

3. Re: situchan's comment on removing manual memoization

In BaseSearchList/index.tsx:63 — the useCallback around handleFocusByIndex is also important here because useStableIndexedHandler requires a stable handler input. If React Compiler can guarantee memoization of handleFocusByIndex, then the manual useCallback could be removed. But since the hook's contract explicitly requires a stable reference, keeping the useCallback makes the contract explicit and safe regardless of compiler behavior. I'd lean toward keeping it for clarity, but deferring to the team's preference on compiler trust.

4. Re: Codex review comment

The Codex comment about handleFocusByIndex being "recreated on every render" is incorrect — it is wrapped in useCallback with [setFocusedIndex] as the dependency, and setFocusedIndex is a state setter (stable). So handleFocusByIndex is stable, getOnFocus is stable, and the optimization works as intended.

5. Tests

Tests are thorough and cover the key behaviors including the stale-handler edge case. Nice work documenting the contract through tests.

---

Next Steps: Reply with @MelvinBot <your feedback> to continue the discussion.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Hooray!

ℹ️ About Codex in GitHub

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• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

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[TMisiukiewicz]

@situchan I compared the output of the compiler with and without useCallback here, and it's the same. Getting rid of it now

[MelvinBot]

Updated Review (post 0384521)

All checks pass. The useCallback removal in 0384521 is fine — React Compiler Compliance passes, confirming the compiler handles memoization here.

One open item from my previous review: The stale-closure cache issue in useStableIndexedHandler still isn't addressed. In this specific usage it's safe because handleFocusByIndex only captures setFocusedIndex (stable state setter), so even stale cached closures behave correctly. But if this hook gets reused with a handler whose captured values change between renders, cached entries will silently call the old handler.

A simple guard would prevent future foot-guns:

const prevHandlerRef = useRef(handler);
if (prevHandlerRef.current !== handler) {
    cacheRef.current = new Map();
    prevHandlerRef.current = handler;
}

This is a "nice to have" for robustness, not a blocker — the current usage is correct. Everything else looks good.

---

Next Steps: Reply with @MelvinBot <your feedback> to continue the discussion.

[situchan]

Bug in production:
Press Enter on focused LHN opens expense detail page

bug.mov

[mountiny]

Thanks for this, looks like it could be impactful but also made me wonder if this is a common issue in our lists - if yes, lets make holistical fix

[mountiny]

Are there other lists in the app that would suffer from this same rerendering bug? @TMisiukiewicz @situchan ? if so, can you track them down and create some holistic solution to fix it for these lists and make sure each new list uses optimized solution?

[mountiny]

Created this issue #90659

[github-actions]

🚧 @mountiny has triggered a test Expensify/App build. You can view the workflow run here.

[github-actions]

🧪🧪 Use the links below to test this adhoc build on Android, iOS, and Web. Happy testing! 🧪🧪
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[OSBotify]

✋ This PR was not deployed to staging yet because QA is ongoing. It will be automatically deployed to staging after the next production release.

[TMisiukiewicz]

Regarding Melvin's comment: I think this would be adding a defensive code for a hypothetical future misuse that doesn't currently exist

[OSBotify]

🚀 Deployed to staging by https://github.com/mountiny in version: 9.3.74-7 🚀

platform	result
🕸 web 🕸	success ✅
🤖 android 🤖	success ✅
🍎 iOS 🍎	success ✅

Bundle Size Analysis (Sentry):

• Android
• iOS

[MelvinBot]

I reviewed the changes in this PR. This is a purely internal performance optimization that caches onFocus handlers per index in BaseSearchList to prevent unnecessary row re-renders. It introduces a new useStableIndexedHandler hook used only internally.

No help site documentation changes are required — there are no user-facing behavior changes, new features, UI modifications, or workflow updates in this PR.

[OSBotify]

🚀 Deployed to production by https://github.com/Beamanator in version: 9.3.74-7 🚀

platform	result
🕸 web 🕸	success ✅
🤖 android 🤖	success ✅
🍎 iOS 🍎	success ✅