8000 Bug: useEffect() clears timeout immediately after a focus event with StrictMode · Issue #33008 · facebook/react · GitHub
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Bug: useEffect() clears timeout immediately after a focus event with StrictMode #33008

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layershifter opened this issue Apr 24, 2025 · 1 comment
Open

Bug: useEffect() clears timeout immediately after a focus event with StrictMode #33008

layershifter opened this issue Apr 24, 2025 · 1 comment
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Status: Unconfirmed A potential issue that we haven't yet confirmed as a bug

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@layershifter
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React version: 18.3.1

Steps To Reproduce

  1. Navigate with keyboard to "toggle menu", press Enter
  2. Notice that a menu is opened, but a tooltip does not exist 🚨

Link to code example: https://stackblitz.com/edit/vitejs-vite-nnvwzvcm

The current behavior

2025-04-24.13.50.07.mp4 
Menu:useEffect() // moves focus to MenuItem ✅ 
MenuItem:onFocus() => Tooltip:onFocus() // triggers a setTimeout() to open Tooltip ✅ 
Tooltip:useEffect:dispose() // calls clearTimeout() 🚨

The expected behavior

Without StrictMode a dispose function is not called:

2025-04-24.13.51.24.mp4

That's a simplified version of the issue from microsoft/fluentui#34296. I clearly understand that it's not a bug in React. It does what's expected 👍

The correct approach is to fire setTimeout() & clearTimeout() in useEffect(). The problem is that the described pattern is not unique and adopted by component libraries:

So we are wondering what is a proper solution in case and looking for guidance in this particular case 🙏
@layershifter layershifter added the Status: Unconfirmed A potential issue that we haven't yet confirmed as a bug label Apr 24, 2025
@szhsin
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szhsin commented Apr 26, 2025

Just stumbled across this issue. I think you can drop the clearTimeout in the useEffect entirely, since there's no harm in calling setState on an unmounted component.

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