Prefer fast-equals over lodash/isEqual.

[Krishna2323]

Explanation of Change

Fixed Issues

$ #61751
PROPOSAL: #61751 (comment)

Tests

• Import isEqual from lodash

• Run npm run lint

• Verify error is shown in terminal: Please use 'deepEqual' from 'fast-equals' instead.

• Verify that no errors appear in the JS console

Offline tests

N/A

QA Steps

N/A

• 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
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Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

MacOS: Desktop

[melvin-bot]

Hey! I see that you made changes to our Form component. Make sure to update the docs in FORMS.md accordingly. Cheers!

[melvin-bot]

@eVoloshchak 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]

[Krishna2323]

There are some ESLint issues, I'll address them tomorrow.

[roryabraham]

@Krishna2323 lint and tests are failing here

[roryabraham]

I'd be ok ignoring unrelated ESLint changed files failures because this PR touches a lot of files and I don't want to increase the risk of this change by making unrelated changes. But jest tests should be fixed.

We should see if the Reassure failure is reproducible locally, but my guess is that it's a false negative, since apples-to-apples fast-equals is much faster than lodashEquals

[Krishna2323]

@eVoloshchak @roryabraham, after some investigation, I found that the Jest Unit Tests fails because of using deepEqual in PopoverWithMeasuredContent.

App/src/components/PopoverWithMeasuredContent.tsx

Lines 194 to 201 in 7e167cc

	export default React.memo(PopoverWithMeasuredContent, (prevProps, nextProps) => {
	if (prevProps.isVisible === nextProps.isVisible && nextProps.isVisible === false) {
	return true;
	}
	return isEqual(prevProps, nextProps);
	});
	export type {PopoverWithMeasuredContentProps};

The issue you're encountering — "RangeError: Maximum call stack size exceeded" — when using deepEqual from 'fast-equals' instead of lodash's isEqual in React.memo — typically comes from a recursive loop or a circular reference in your props that deepEqual fails to handle correctly.

RCA from chatGPT

Breakdown of Why deepEqual Fails:

• fast-equals is faster than lodash.isEqual because it assumes certain usage patterns and optimizes accordingly.
• However, it doesn't handle circular references as robustly as lodash.isEqual.
• If your props (like children, refs, or styles from hooks) contain circular or deeply nested structures, deepEqual can fall into infinite recursion, leading to a Maximum call stack size exceeded error.

Why isEqual Works:

• lodash.isEqual is more defensive and mature.
• It handles circular references, Map/Set, and React elements better than fast-equals.
• It's slower, but safer for general-purpose usage — especially in React environments where props can contain complex objects (e.g., React elements, styles, hooks' returns).

---

What You Can Do:

1. Stick to isEqual for React.memo comparisons unless you are certain there are no circular references or deeply nested dynamic props.
2. Profile the component to confirm whether isEqual is causing a performance bottleneck — often, it's not a problem.
3. If you're determined to use fast-equals, consider using createCustomEqual with a custom handler that safely breaks circular references, though that adds complexity.

---

TL;DR

Use lodash.isEqual for safer deep comparisons in React.memo.
fast-equals (deepEqual) is faster but not robust against circular or complex React props, which is why it crashes with a stack overflow.

Use lodash.isEqual for safer deep comparisons in React.memo.fast-equals (deepEqual) is faster but not robust against circular or complex React props, which is why it crashes with a stack overflow.

[roryabraham]

Ah, yes so fast-equals provides a method circularDeepEquals which can be used to support circular structures. It's a bit slower so should only be used when needed. But I think we should prefer that over lodash.isEqual because it makes it very clear why it's being used instead of deepEquals. Couldn't find an existing benchmark comparing the two for circular structures though

[roryabraham]

Maybe we should also upgrade fast-equals to latest. It looks like there are some bug fixes there, but also a >100% speed improvement for maps and sets

[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. ⚠️

[Krishna2323]

@roryabraham, all tests are passing now (except for a few unrelated ESLint issues).

@eVoloshchak, could you please review this comment and review the changes? Thanks!

[eVoloshchak]

@Krishna2323, could you please open a separate PR for the fast-equals update and hold this one for it?

[Krishna2323]

@eVoloshchak, PR for updating fast-equals is open.

[Krishna2323]

@eVoloshchak, the fast-equals update is on staging. Do we need to wait for it to be deployed to production, or are we good to move forward?

[eVoloshchak]

Do we need to wait for it to be deployed to production, or are we good to move forward?

@Krishna2323, we are good to move forward
There's still an ESLint error, doesn't look like it's related to these changes, could you pull the latest main please?

[eVoloshchak]

@Krishna2323, some checks are failing

[Krishna2323]

@eVoloshchak ESLint is fixed.

[eVoloshchak]

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
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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).
  • 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
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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.
  • 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
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• 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)
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  • 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.
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Screenshots/Videos

Android: HybridApp

Android: mWeb Chrome

iOS: HybridApp

iOS: mWeb Safari

MacOS: Chrome / Safari

MacOS: Desktop

[eVoloshchak]

LGTM!

[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.

[izarutskaya]

Hi @Krishna2323 If we don't need QA for this, can I check it off?

QA Steps
N/A

[github-actions]

🚀 Deployed to staging by https://github.com/roryabraham in version: 9.1.67-0 🚀

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

[github-actions]

🚀 Deployed to production by https://github.com/lakchote in version: 9.1.67-2 🚀

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