fix: use microtask queue for whatwg-fetch XHR events by rohit9625 · Pull Request #94399 · Expensify/App

rohit9625 · 2026-06-24T04:39:31Z

Explanation of Change

In React Native (iOS), we observed cases where:

The network request completed successfully.
xhr.onload executed successfully.
The scheduled timeout was significantly delayed until a later user interaction or navigation event.
The fetch promise remained unresolved until that timeout executed.

Because the promise resolution depends on a timer, any environment-specific issue affecting timer delivery can prevent completed requests from resolving promptly.

So this PR replaces setTimeout(0) with queueMicrotask for XHR event handlers within the whatwg-fetch polyfill.

Why queueMicrotask? : Microtasks are generally executed as part of the current JavaScript turn after the current call stack unwinds and do not depend on timer infrastructure. Also, I don't see any benefit of using setTimeout here because we are passing 0 as a timeout that is supposed to be executed as soon as possible. So, we should better use queueMicrotask here.

Fixed Issues

$ #90309
PROPOSAL: $ #90309 (comment)

Tests

Open the Expensify app
Navigate to the workspace chat and create a report
Add one expense with any amount
Split the expense from step 2
Open one of the child expenses
Click More -> Edit splits
Select one split and click Remove Split
Click save
Make sure the expense report loads normally and display the expense details without any UI interaction.

Verify that no errors appear in the JS console

Offline tests

Open the Expensify app
Navigate to the workspace chat and create a report
Add one expense with any amount
Split the expense from step 2
Force offline or turn off the internet
Open one of the child expenses
Click More -> Edit splits
Select one split and click Remove Split
Click save
You should see the Not Here page, then navigate back
Now, turn on the internet
Make sure the expense report loads normally and displays the expense details without any UI interaction.

QA Steps

// TODO: These must be filled out, or the issue title must include "[No QA]."
Same as tests

Verify that no errors appear in the JS console

PR Author Checklist

Screenshots/Videos

Android: Native

Screen.Recording.2026-06-24.at.9.15.44.AM.mov

Android: mWeb Chrome

Screen.Recording.2026-06-24.at.8.30.50.AM.mov

iOS: Native

Screen.Recording.2026-06-24.at.8.49.51.AM.mov

iOS: mWeb Safari

Screen.Recording.2026-06-24.at.8.41.16.AM.mov

MacOS: Chrome / Safari

Screen.Recording.2026-06-24.at.8.21.36.AM.mov

Replaces `setTimeout(0)` with `queueMicrotask` for XHR event handlers within the `whatwg-fetch` polyfill.

github-actions · 2026-06-24T04:39:39Z

⚠️ 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 · 2026-06-24T04:50:18Z

@dmkt9 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]

dmkt9 · 2026-06-25T02:50:27Z

@rohit9625 I think we should address the "Not Found" page bug mentioned here as well: #90309 (comment). This bug could block QA from testing the fix.

rohit9625 · 2026-06-25T06:40:46Z

Well, I can fix that bug too. Let me check if we have existing tickets for this bug :)

rohit9625 · 2026-06-25T09:56:58Z

I didn't find any existing GitHub issues for that Not Here page bug. Also, I can reproduce that on the web target only. So, are you sure that we should fix that issue in the same PR, @dmkt9?

dmkt9 · 2026-06-25T10:42:35Z

@rohit9625 Yes. Although it has a different root cause, the reproduction steps are the same as the original bug, so I think it should be addressed in this PR as well. Additionally, I can reproduce it on Android and iOS as well.

rohit9625 · 2026-06-25T10:45:36Z

@rohit9625 Yes. Although it has a different root cause, the reproduction steps are the same as the original bug, so I think it should be addressed in this PR as well.

Okay, working on the fix now.

Additionally, I can reproduce it on Android and iOS as well.

Strange, I can only reproduce it on the web (wide-layout) because that uses a different component and it was not reproducible for narrow layout. I'm fixing the issue on web and I think it will fix it on other platforms as well.

dmkt9 · 2026-06-25T10:52:27Z

Okay, working on the fix now.

Thanks.

Strange, I can only reproduce it on the web (wide-layout) because that uses a different component and it was not reproducible for narrow layout. I'm fixing the issue on web and I think it will fix it on other platforms as well.

Can you try reproducing it on the Report page?

2026-06-25.17-50-10.mp4

rohit9625 · 2026-06-25T11:47:19Z

Sorry, it took a bit building the Android app and yes, it is reproducible via Spend -> Reports page. Could you please confirm the expected behavior here?
Because when offline, the Not Here page persists until reconnected to the internet. However, if not offline that page appears for few seconds I guess, until the API request is complete. So, it's clear that something to do with optimistic data, I just need to confirm what should we show optimistically?

dmkt9 · 2026-06-25T14:34:40Z

@rohit9625 I think we don't need to handle that bug ourselves, since we already have a similar issue tracked here: #91917

rohit9625 · 2026-06-25T16:00:00Z

Ohh, I missed that issue. Yeah, you're right we don't need to fix that issue in this PR right now. So, are we good to go with merging this PR, @dmkt9?

rohit9625 · 2026-06-26T14:41:03Z

The reason I think that the Not Here page issue will not block testing this PR is that the current issue is about infinite loading, which is resolved by this PR. The Not Here page will be visible for a moment if online, and that too via the Spend -> Reports flow.

dmkt9 · 2026-06-27T14:48:56Z

@rohit9625 From my testing, this PR looks good. However, just to be safe, could you merge the latest main branch when you have a chance? I'll request an ad hoc build afterward and test it to ensure everything is working as expected.

rohit9625 · 2026-06-27T15:10:07Z

I've merged the main branch, @dmkt9. Please trigger an Adhoc build, I also want to test on Adhoc build because locally its very laggy sometimes.

dmkt9 · 2026-06-27T15:16:43Z

Thanks. I'll ask someone to help trigger it.

rohit9625 · 2026-06-29T07:46:16Z

Hi @dmkt9, did you ask somebody? If appropriate, I can drop a message on Slack for this :)

dmkt9 · 2026-06-29T08:00:30Z

Hi @dmkt9, did you ask somebody?

Yes. I did

github-actions · 2026-06-30T15:04:37Z

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

dmkt9 · 2026-06-30T15:42:28Z

@puneetlath Could you please re-trigger the build? I noticed the Android build failed

rohit9625 · 2026-07-01T15:18:01Z

Hi @puneetlath, Friendly bump on the above comment!
I also just merged the main branch :)

puneetlath · 2026-07-01T16:31:09Z

Triggered again!

github-actions · 2026-07-01T16:34:27Z

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

rohit9625 · 2026-07-01T17:05:53Z

Just tested the Adhoc Android build and it works as expected :)

dmkt9 · 2026-07-02T05:04:52Z

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
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 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)
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)
If a new component is created I verified that:
- A similar component doesn't exist in the codebase
- All props are defined accurately and each prop has a /** comment above it */
- The file is named correctly
- The component has a clear name that is non-ambiguous and the purpose of the component can be inferred from the name alone
- The only data being stored in the state is data necessary for rendering and nothing else
- For Class Components, any internal methods passed to components event handlers are bound to this properly so there are no scoping issues (i.e. for onClick={this.submit} the method this.submit should be bound to this in the constructor)
- Any internal methods bound to this are necessary to be bound (i.e. avoid this.submit = this.submit.bind(this); if this.submit is never passed to a component event handler like onClick)
- All JSX used for rendering exists in the render method
- The component has the minimum amount of code necessary for its purpose, and it is broken down into smaller components in order to separate concerns and functions
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.
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.hybrid.mp4

Android: mWeb Chrome

android.chrome.mp4

iOS: HybridApp

ios.hybrid.mp4

iOS: mWeb Safari

ios.safari.mp4

MacOS: Chrome / Safari

mac.safari.mp4

dmkt9

LGTM.

Since our fetch implementation now uses a microtask, I was a bit concerned that it might block the JS thread if there were a large number of requests in the network queue. However, I thought the risk was low because fetch itself is not a microtask, so we shouldn't end up with a long chain of microtasks.

To be safe, I tested it on an ad hoc build, and everything worked as expected without any noticeable impact.

rohit9625 · 2026-07-03T17:33:55Z

Hi @puneetlath, we are waiting for you to review the PR :)
Also, please check the above comment.

rohit9625 · 2026-07-06T14:21:53Z

Friendly bump! @puneetlath :)

github-actions · 2026-07-06T15:09:17Z

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

OSBotify · 2026-07-06T15:09:53Z

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

github-actions · 2026-07-06T15:37:41Z

🧪🧪 Use the links below to test this adhoc build on Android, iOS, and Web. Happy testing! 🧪🧪
Built from App PR #94399.

Android 🤖	iOS 🍎
https://ad-hoc-expensify-cash.s3.us-east-1.amazonaws.com/rock-artifacts/ad-hoc/rock-android-Adhoc-26ea718e9c5-d388d60-68f94e37d087c335a7088235cbdbe92e301babc7/index.html	https://ad-hoc-expensify-cash.s3.us-east-1.amazonaws.com/rock-artifacts/ad-hoc/rock-ios-device-AdHoc-26ea718-d388d60-3a0b5dc3bd42d6186d8b5de27b10ea0fc70f6a1a/index.html

Web 🕸️
https://94399.pr-testing.expensify.com

👀 View the workflow run that generated this build 👀

OSBotify · 2026-07-06T15:46:26Z

🚀 Deployed to staging by https://github.com/puneetlath in version: 9.4.28-0 🚀

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

OSBotify · 2026-07-07T17:54:10Z

🚀 Deployed to production by https://github.com/mountiny in version: 9.4.28-2 🚀

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

Bundle Size Analysis (Sentry):

Android

fix: use microtask queue for whatwg-fetch XHR events

3aa85ac

Replaces `setTimeout(0)` with `queueMicrotask` for XHR event handlers within the `whatwg-fetch` polyfill.

melvin-bot Bot assigned rohit9625 Jun 24, 2026

docs: add details.md file for whatwg-fetch patches

cf330ac

rohit9625 marked this pull request as ready for review June 24, 2026 04:50

rohit9625 requested a review from a team as a code owner June 24, 2026 04:50

melvin-bot Bot requested review from dmkt9 and removed request for a team June 24, 2026 04:50

Merge branch 'Expensify:main' into fix/network-responses-stuck

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rohit9625 added 2 commits June 30, 2026 21:16

Merge branch 'Expensify:main' into fix/network-responses-stuck

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Merge branch 'Expensify:main' into fix/network-responses-stuck

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dmkt9 approved these changes Jul 2, 2026

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melvin-bot Bot requested a review from puneetlath July 2, 2026 05:09

puneetlath approved these changes Jul 6, 2026

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puneetlath merged commit 26ea718 into Expensify:main Jul 6, 2026
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OSBotify mentioned this pull request Jul 6, 2026

Deploy Checklist: New Expensify 2026-07-06 #95398

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melvin-bot Bot mentioned this pull request Jul 7, 2026

[Due for payment 2026-07-14] [$250] iOS - Report - Expense report loads infinitely after deleting one split #90309

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Explanation of Change

Fixed Issues

Tests

Offline tests

QA Steps

PR Author Checklist

Screenshots/Videos

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