[Due for payment 2025-02-13] [$250] Log in - Login page scroll to top on change language

[lanitochka17]

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Version Number: 9.0.86-2
Reproducible in staging?: Y
Reproducible in production?: Y
If this was caught on HybridApp, is this reproducible on New Expensify Standalone?: Y
If this was caught during regression testing, add the test name, ID and link from TestRail: N/A
Issue reported by: Applause - Internal Team

Action Performed:

Preconditions: User should be logged out

1. Open https://staging.new.expensify.com/
2. Scroll to bottom
3. Change language

Expected Result:

Page position should not be changed

Actual Result:

Login page scroll to top

Workaround:

Unknown

Platforms:

Which of our officially supported platforms is this issue occurring on?

• Android: Standalone
• Android: HybridApp
• Android: mWeb Chrome
• iOS: Standalone
• iOS: HybridApp
• iOS: mWeb Safari
• MacOS: Chrome / Safari
• MacOS: Desktop

Screenshots/Videos

Add any screenshot/video evidence

Bug6698620_1734580924023.295.mp4

View all open jobs on GitHub

555555555.mp4

Upwork Automation - Do Not Edit

• Upwork Job URL: https://www.upwork.com/jobs/~021881832199834454313
• Upwork Job ID: 1881832199834454313
• Last Price Increase: 2025-01-21
• Automatic offers:
• linhvovan29546 | Contributor | 105899583

Issue Owner

Current Issue Owner: @johncschuster

[melvin-bot]

Triggered auto assignment to @johncschuster (Bug), see https://stackoverflow.com/c/expensify/questions/14418 for more details. Please add this bug to a GH project, as outlined in the SO.

[github-actions]

⚠️ @Shahidullah-Muffakir Thanks for your proposal. Please update it to follow the proposal template, as proposals are only reviewed if they follow that format (note the mandatory sections).

[github-actions]

⚠️ @Shahidullah-Muffakir Thanks for your proposal. Please update it to follow the proposal template, as proposals are only reviewed if they follow that format (note the mandatory sections).

[mohit6789]

🚨 Edited by proposal-police: This proposal was edited at 2025-01-16 21:58:56 UTC.

Proposal

Please re-state the problem that we are trying to solve in this issue.

Login page scroll to top on change language

What is the root cause of that problem?

Because we passed prevPreferredLocale in dependancy array of useEffect here it rerun whenever prevPreferredLocale value change. prevPreferredLocale is not state/props so we should not pass it in dependancy array.

App/src/pages/signin/SignInPageLayout/index.tsx

Line 50 in 784f3aa

const prevPreferredLocale = usePrevious(preferredLocale);

What changes do you think we should make in order to solve the problem?

Remove prevPreferredLocale from dependancy array fix this issue.

App/src/pages/signin/SignInPageLayout/index.tsx

Line 82 in 784f3aa

}, [welcomeHeader, welcomeText, prevPreferredLocale, preferredLocale]);

Note: We should not remove this block because welcomeHeader and welcomeText are change based on some logic from here. So we should scroll to top whenever welcomeHeader and welcomeText are changed.

What specific scenarios should we cover in automated tests to prevent reintroducing this issue in the future?

NA

What alternative solutions did you explore? (Optional)

[drminh2807]

Proposal

Please re-state the problem that we are trying to solve in this issue.

Log in - Login page scroll to top on change language

What is the root cause of that problem?

Here’s a rewritten version of your text with improved clarity and flow:

The SignInPageLayout component rerenders twice when the locale changes because both navigateFocus and children are updated. As a result, const prevPreferredLocale = usePrevious(preferredLocale); doesn't behave as intended.

Evidence of this can be observed by commenting out both properties—while the UI may display hidden components, the rerendering issue no longer occurs.

What changes do you think we should make in order to solve the problem?

To address this, we should use an alternative method to track prevPreferredLocale.

App/src/pages/signin/SignInPageLayout/index.tsx

Lines 76 to 82 in 57f544f

	useEffect(() => {
	if (prevPreferredLocale !== preferredLocale) {
	return;
	}
	scrollPageToTop();
	}, [welcomeHeader, welcomeText, prevPreferredLocale, preferredLocale]);

    const prevPreferredLocale = useRef(preferredLocale);
    useEffect(() => {
        if (prevPreferredLocale.current !== preferredLocale) {
            prevPreferredLocale.current = preferredLocale;
            return;
        }

        scrollPageToTop();
    }, [welcomeHeader, welcomeText, preferredLocale]);

What specific scenarios should we cover in automated tests to prevent reintroducing this issue in the future?

N/A

What alternative solutions did you explore? (Optional)

N/A

[melvin-bot]

@johncschuster Whoops! This issue is 2 days overdue. Let's get this updated quick!

[melvin-bot]

Job added to Upwork: https://www.upwork.com/jobs/~021881832199834454313

[melvin-bot]

Triggered auto assignment to Contributor-plus team member for initial proposal review - @hungvu193 (External)

[huult]

Proposal

Please re-state the problem that we are trying to solve in this issue.

Login page scroll to top on change language

What is the root cause of that problem?

The reason SignInPageLayout triggers a re-render twice when the locale is changed is that prevPreferredLocale gets assigned both the old and new values. As a result, when prevPreferredLocale holds the old value, the condition to scroll to the top is validated, causing this issue

App/src/pages/signin/SignInPageLayout/index.tsx

Line 31 in 81f38b0

function SignInPageLayout(

and the component re-renders due to stale references if signInPageLayoutRef.current changes after the assignment

App/src/pages/signin/SignInPage.tsx

Line 325 in 550b32b

scrollPageToTop={signInPageLayoutRef.current?.scrollPageToTop}

What changes do you think we should make in order to solve the problem?

To resolve this issue, use an arrow function that wraps the scrollPageToTop call. This ensures signInPageLayoutRef.current is accessed at execution time, keeping the reference up-to-date and preventing SignInPageLayout from triggering unnecessary re-renders

App/src/pages/signin/SignInPage.tsx

Line 325 in 550b32b

scrollPageToTop={signInPageLayoutRef.current?.scrollPageToTop}

update to:

    scrollPageToTop={() => {
        signInPageLayoutRef.current?.scrollPageToTop();
    }}

POC

Screen.Recording.2025-01-22.at.15.53.08.mp4

What specific scenarios should we cover in automated tests to prevent reintroducing this issue in the future?

This is a UI bug and does not require testing.

What alternative solutions did you explore? (Optional)

Reminder: Please use plain English, be brief and avoid jargon. Feel free to use images, charts or pseudo-code if necessary. Do not post large multi-line diffs or write walls of text. Do not create PRs unless you have been hired for this job.

[hungvu193]

Update: I'll review the proposals tomorrow.

[hungvu193]

Still under reviewing

[linhvovan29546]

🚨 Edited by proposal-police: This proposal was edited at 2025-01-24 10:56:54 UTC.

Proposal

Please re-state the problem that we are trying to solve in this issue.

Log in - Login page scroll to top on change language

What is the root cause of that problem?

This issue occurs because the language change triggers a useEffect in the code.

App/src/pages/signin/SignInPageLayout/index.tsx

Lines 76 to 82 in aa849f1

	useEffect(() => {
	if (prevPreferredLocale !== preferredLocale) {
	return;
	}
	scrollPageToTop();
	}, [welcomeHeader, welcomeText, prevPreferredLocale, preferredLocale]);

When the welcomeHeader or welcomeText changes, it causes the page to scroll to the top. This behavior seems to be related to a previous issue that was fixed in PR #21815.
However, the issue has resurfaced because the component re-renders twice, which leads to the condition prevPreferredLocale !== preferredLocale evaluating to false, which leads to the page scrolling to the top

What changes do you think we should make in order to solve the problem?

I suggest removing the useEffect

App/src/pages/signin/SignInPageLayout/index.tsx

Lines 76 to 82 in aa849f1

	useEffect(() => {
	if (prevPreferredLocale !== preferredLocale) {
	return;
	}
	scrollPageToTop();
	}, [welcomeHeader, welcomeText, prevPreferredLocale, preferredLocale]);

Why should we remove it?
This useEffect was introduced in PR #17445 to ensure the page scrolls to the top when clicking actions like "Create A New Account," "Log In," "Go Back," or "Forget." However, this functionality is now handled by a separate implementation introduced in PR #33743, making this useEffect redundant.

POC

Before	After
page-scroll-to-top-before.mp4	page-scoll-to-top-after.mp4

What specific scenarios should we cover in automated tests to prevent reintroducing this issue in the future?

NA

What alternative solutions did you explore? (Optional)

Reminder: Please use plain English, be brief and avoid jargon. Feel free to use images, charts or pseudo-code if necessary. Do not post large multi-line diffs or write walls of text. Do not create PRs unless you have been hired for this job.

[hungvu193]

Thanks everyone for the proposals. After checking carefully. I agree with @linhvovan29546 's proposal here. We should remove this block of code. It was added to solve #16357 but it was resolved with #33743 and we don't need it anymore.

🎀 👀 🎀 C+ reviewed

[melvin-bot]

Triggered auto assignment to @robertjchen, see https://stackoverflow.com/c/expensify/questions/7972 for more details.

[robertjchen]

Thanks for the detailed review and proposals. Let's go with @linhvovan29546 's proposal 👍

[melvin-bot]

📣 @linhvovan29546 🎉 An offer has been automatically sent to your Upwork account for the Contributor role 🎉 Thanks for contributing to the Expensify app!

Offer link
Upwork job
Please accept the offer and leave a comment on the Github issue letting us know when we can expect a PR to be ready for review 🧑‍💻
Keep in mind: Code of Conduct | Contributing 📖

[linhvovan29546]

PR is ready for review!

[melvin-bot]

Reviewing label has been removed, please complete the "BugZero Checklist".

[melvin-bot]

The solution for this issue has been 🚀 deployed to production 🚀 in version 9.0.94-25 and is now subject to a 7-day regression period 📆. Here is the list of pull requests that resolve this issue:

• fix: login page auto scroll to top after change language #55929

If no regressions arise, payment will be issued on 2025-02-13. 🎊

For reference, here are some details about the assignees on this issue:

• @hungvu193 requires payment through NewDot Manual Requests
• @linhvovan29546 requires payment automatic offer (Contributor)

[melvin-bot]

@hungvu193 @johncschuster @hungvu193 The PR fixing this issue has been merged! The following checklist (instructions) will need to be completed before the issue can be closed. Please copy/paste the BugZero Checklist from here into a new comment on this GH and complete it. If you have the K2 extension, you can simply click: [this button]

[johncschuster]

BugZero Checklist:

• [Contributor] Classify the bug:

Bug classification

Source of bug:

• 1a. Result of the original design (eg. a case wasn't considered)
• 1b. Mistake during implementation
• 1c. Backend bug
• 1z. Other:

Where bug was reported:

• 2a. Reported on production (eg. bug slipped through the normal regression and PR testing process on staging)
• 2b. Reported on staging (eg. found during regression or PR testing)
• 2d. Reported on a PR
• 2z. Other:

Who reported the bug:

• 3a. Expensify user
• 3b. Expensify employee
• 3c. Contributor
• 3d. QA
• 3z. Other:

• [Contributor] The offending PR has been commented on, pointing out the bug it caused and why, so the author and reviewers can learn from the mistake.

  Link to comment:

• [Contributor] If the regression was CRITICAL (e.g. interrupts a core flow) A discussion in #expensify-open-source has been started about whether any other steps should be taken (e.g. updating the PR review checklist) in order to catch this type of bug sooner.

  Link to discussion:

• [Contributor] If it was decided to create a regression test for the bug, please propose the regression test steps using the template below to ensure the same bug will not reach production again.

Regression Test Proposal Template

• [BugZero Assignee] Create a GH issue for creating/updating the regression test once above steps have been agreed upon.

  Link to issue:

Regression Test Proposal

Precondition:

Test:

Do we agree 👍 or 👎

[johncschuster]

Payment Summary

Contributor: @linhvovan29546 paid $250 via Upwork (will be paid after BZ Checklist and regression threshold window has been crossed)
Contributor+: @hungvu193 owed $250 via NewDot

[melvin-bot]

@robertjchen @johncschuster @hungvu193 @linhvovan29546 this issue is now 4 weeks old, please consider:

• Finding a contributor to fix the bug
• Closing the issue if BZ has been unable to add the issue to a VIP or Wave project
• If you have any questions, don't hesitate to start a discussion in #expensify-open-source

Thanks!

[hungvu193]

BugZero Checklist:

• [Contributor] Classify the bug:

Bug classification

Source of bug:

• 1a. Result of the original design (eg. a case wasn't considered)
• 1b. Mistake during implementation
• 1c. Backend bug
• 1z. Other: We changed the design and this bug is happening again.

Where bug was reported:

• 2a. Reported on production (eg. bug slipped through the normal regression and PR testing process on staging)
• 2b. Reported on staging (eg. found during regression or PR testing)
• 2d. Reported on a PR
• 2z. Other:

Who reported the bug:

• 3a. Expensify user
• 3b. Expensify employee
• 3c. Contributor
• 3d. QA
• 3z. Other:

• [Contributor] The offending PR has been commented on, pointing out the bug it caused and why, so the author and reviewers can learn from the mistake.

  Link to comment: We don't have offending PR for this issue, the behavior was changed and the block of code that we added to fix the previous issue is now redundant.

• [Contributor] If the regression was CRITICAL (e.g. interrupts a core flow) A discussion in #expensify-open-source has been started about whether any other steps should be taken (e.g. updating the PR review checklist) in order to catch this type of bug sooner.

  Link to discussion: N/A

• [Contributor] If it was decided to create a regression test for the bug, please propose the regression test steps using the template below to ensure the same bug will not reach production again.

Test:

1. Logout if you're login.
2. Scroll down to the bottom and change the language.
3. Verify that Login Page doesn't scroll to top.

Do we agree 👍 or 👎

[johncschuster]

Payment has been issued via Upwork to @linhvovan29546! @hungvu193, please request payment via ND! (Summary here)

[garrettmknight]

$250 approved for @hungvu193