fix: inverted flatlist overscroll recoil

[wgsquayson]

Explanation of Change

This PR aims to fix the perceived overscroll recoil or rubber band effect of the inverted flatlists, introduced on react-native-web's patch 008. It happened because the ev.preventDefault on the inverted wheel event handler was not being fired when the scroll reached the list edges. It does not affect the bidirectional scroll introduced on patches 008 and 009 of react-native-web.

Fixed Issues

$ #66821
PROPOSAL: Add a conditional on the inverted wheel handler to execute ev.preventDefault when the scrolling reaches the list edges.

Tests

PS: It's only reproducible on web/desktop
PS2: It's not reproducible with a mouse, only with a trackpad.

1. Checkout to this branch and run rm -rf node_modules
2. Run npm install
3. Run the web/desktop project and sign in
4. Open a report that uses an inverted flatlist as a component (e. g. Concierge)
5. Scroll to the top or to the bottom of the list, and slowly try to overscroll it
6. No jumping/recoil/rubber band effect should be perceived

Offline tests

Same as tests

QA Steps

Same as tests

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
  • I added steps for Staging and/or Production testing in the QA steps section
  • 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).
• I included screenshots or videos for tests on all platforms
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  • Android: mWeb Chrome
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  • MacOS: Chrome / Safari
  • MacOS: Desktop
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Screenshots/Videos

MacOS: Chrome / Safari

A new project showing that the bidirectional scroll is still working, with the same inverted flatlist wheel handler

dumb-project.mov

chrome.mov

MacOS: Desktop

safari.mov

[github-actions]

⚠️ This PR is possibly changing native code and/or updating libraries, it may cause problems with HybridApp. Please check if any patch updates are required in the HybridApp repo and run an AdHoc build to verify that HybridApp will not break. Ask Contributor Plus for help if you are not sure how to handle this. ⚠️

[melvin-bot]

@hungvu193 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]

[hungvu193]

Thanks @wgsquayson. I took a few tests and I think it's fixed 🎉 . Could you share a bit more about the RCA and solution so I could have more context? Ty

[wgsquayson]

Hey @hungvu193
Sure, let me break it down

• I first tried to reproduce it, and I noticed It was not reproducible w/ a mouse, and that's because trackpad events are emitted way more frequently than mouse
• Then I went to multiple reports and tried to reproduce it, I noticed that it was only happening with flatlists with the prop inverted as true
• Then I went directly to the InvertedFlatList component, and tried to tweak some things there, such as overscroll behavior styles and scroll handler functions. None worked.
• I created a new project and tried to reproduce the recoil effect. Was not successful as well, the effect did not happen.
• I went through a bunch of issues about FlatLists on the react-native-web repo, almost nothing helped, but it showed me that the react-native-web has a custom handler for wheel events on virtualized lists w/ the inverted prop. But I was still a bit lost on what causing it.
• I was reading some stuff about patch-package and something snapped on my mind, i went directly to expensify's patches and noticed a bunch of rn web patches. I erased them and the behavior ceased. Then I added one by one that patched the virtualized list, when patch 008 was added again the behavior came back.
• I noticed that on the unpatched rn web wheel handler, ev.preventDefault() was being called on every execution of the inverted list wheel handler. I added a log on the code after patch to check if it was being called on the list edges. It was not. So, I added a conditional to execute It.

[blimpich]

For some reason the ad-hoc build didn't work, restarting it now

[blimpich]

started a new build here: https://github.com/Expensify/App/actions/runs/17134727083

[github-actions]

🚧 @blimpich 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, Desktop, and Web. Happy testing! 🧪🧪
Built from App PR #68895.

Android 🤖	iOS 🍎
https://ad-hoc-expensify-cash.s3.amazonaws.com/android/68895/index.html	https://ad-hoc-expensify-cash.s3.amazonaws.com/ios/68895/index.html

Desktop 💻	Web 🕸️
https://ad-hoc-expensify-cash.s3.amazonaws.com/desktop/68895/NewExpensify.dmg	https://68895.pr-testing.expensify.com

---

👀 View the workflow run that generated this build 👀

[hungvu193]

@wgsquayson Thanks for your detailed explanation 🙏

[hungvu193]

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)
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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
• If a new CSS style is added I verified that:
  • 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.
• For any bug fix or new feature in this PR, I verified that sufficient unit tests are included to prevent regressions in this flow.
• 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.
• I have checked off every checkbox in the PR reviewer checklist, including those that don't apply to this PR.

Screenshots/Videos

Android: HybridApp

Android: mWeb Chrome

iOS: HybridApp

iOS: mWeb Safari

MacOS: Chrome / Safari

Screen.Recording.2025-08-21.at.18.11.28.mov

MacOS: Desktop

Screen.Recording.2025-08-21.at.18.10.11.mov

[melvin-bot]

We did not find an internal engineer to review this PR, trying to assign a random engineer to #66821 as well as to this PR... Please reach out for help on Slack if no one gets assigned!

[rlinoz]

Code looks good, but I can't repro the issue in staging either, so do you want to review as well @blimpich ?

[blimpich]

Tested this locally and it works! Nice job!! 👍

[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.

[OSBotify]

🚀 Deployed to staging by https://github.com/blimpich in version: 9.1.99-0 🚀

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

[yuwenmemon]

FYI the PR for this caused the deploy blocker here and we are reverting it: #69262

[OSBotify]

🚀 Deployed to production by https://github.com/thienlnam in version: 9.1.99-11 🚀

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