Addon A11y: Only run checks in story mode

[kroeder]

Closes #30975

What I did

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

• Checkout branch and compile repo
• Make sure addon-a11y is enabled
• Make sure to enable debug output from axe and add this to the meta part of a story

    parameters: {
        a11y: {
            options: {
                performanceTimer: true,
            },
        },
    },

• Start any Storybook with an MDX file that references a stories.ts file
• In docs mode: Axe should not print anything to console
• In story mode: Axe should print check timings to the console

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.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

Greptile Summary

This PR introduces a viewMode guard in /code/addons/a11y/src/preview.tsx to limit axe-core runs to story mode, improving performance in docs mode.

• Added a condition to check if viewMode equals 'story' before running accessibility checks.
• Prevents unnecessary axe-core execution and slowdown in docs mode.
• Retains complete reporting, error handling, and Vitest integration in story mode.

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[greptile-apps]

LGTM

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[greptile-apps]

LGTM

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[nx-cloud]

View your CI Pipeline Execution ↗ for commit 935af64.

Command	Status	Duration	Result
nx run-many -t build --parallel=3	✅ Succeeded	1m 39s	View ↗

---

☁️ Nx Cloud last updated this comment at 2025-04-22 13:46:58 UTC

[greptile-apps]

LGTM

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[kroeder]

Can someone give me a hint if the test assertions are just wrong or if I broke something with my change? 👀

[greptile-apps]

LGTM

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[yannbf]

Thanks a lot @kroeder!

[kroeder]

@yannbf will you backport this as patch release as well?