Instrumenter: Fix userEvent.type performance regression

[ndelangen]

What I did

Fixes #32435

Add getKeys filter to exclude 'eventWrapper' property from instrumenter calls to prevent performance regression in userEvent.type operations. This addresses the slowdown reported when upgrading from Storybook 8 to 9 with addon-vitest.

The instrumenter was spending significant time sorting large arrays of calls that included the eventWrapper property, which is not needed for testing interactions. By filtering it out at the instrumentation level, we avoid unnecessary processing overhead.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

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Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

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Greptile Summary

Updated On: 2025-09-11 09:06:36 UTC

This PR addresses a performance regression in userEvent.type operations that occurs when upgrading from Storybook 8 to 9, particularly affecting users of addon-vitest. The fix involves filtering out the 'eventWrapper' property from instrumenter calls at two key locations in the testing utilities.

The core issue was that Storybook's instrumenter was processing the 'eventWrapper' property from @testing-library/user-event, which contains large arrays of internal call data. The instrumenter would spend significant time sorting and processing these arrays even though this property isn't needed for testing interactions. By adding a getKeys filter that excludes 'eventWrapper', the PR prevents this unnecessary overhead.

The changes are applied consistently across both testing-library.ts and preview.ts, ensuring that the performance optimization works uniformly for all instrumented testing utilities. The fix is surgical and targeted - it only affects how the instrumenter processes userEvent objects without changing the broader instrumentation behavior or testing functionality.

Confidence score: 4/5

• This PR is safe to merge with low risk of breaking existing functionality
• Score reflects targeted nature of fix and clear understanding of root cause
• Pay close attention to testing-library.ts and preview.ts for consistent filter implementation

[nx-cloud]

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☁️ Nx Cloud last updated this comment at 2025-09-11 12:13:13 UTC

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