watchSlidesProgress repeatedly re-adds classes to slides when scrolling/moving, causing an unnecessary performance penalty

[WesselKroos]

Check that this is really a bug

• I confirm

Reproduction link

https://codesandbox.io/p/sandbox/swiper-default-forked-477vky

Bug description

(This is similar to previously reported performance issue #7355, but for another slide class this time.)

When watchSlidesProgress is enabled every scroll(move) event re-adds the slideVisibleClass and slideFullyVisibleClass classes. This causes a performance penalty because it triggers unnecessary style recalculations on the (semi-)visible slides.

Expected Behavior

The slideVisibleClass and slideFullyVisibleClass classes are only removed or added when necessary:

After.mp4

Actual Behavior

The slideVisibleClass and slideFullyVisibleClass classes are continuously re-added in every scroll(move) event:

Before.mp4

Swiper version

11.1.1

Platform/Target and Browser Versions

All platforms/targets

Validations

• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.
• Make sure this is a Swiper issue and not a framework-specific issue

Would you like to open a PR for this bug?

• I'm willing to open a PR