Problem

When using the Tab key to navigate through links inside Swiper slides, the browser automatically scrolls the container to show the focused element. This changes the scrollLeft/scrollTop property of the wrapper element, which breaks the slider display and causes slides to become misaligned.

This issue affects keyboard accessibility, as users navigating with the Tab key would see the slider break visually.

Solution

The fix prevents the browser's automatic scroll from affecting the slider by:

1. Listening for focusin events: Added a focusin event listener (which fires before focus and bubbles) to catch focus events on focusable elements (links, buttons, inputs, etc.) inside slides.
2. Saving scroll position: When a focusable element gets focus, we immediately save the current scrollLeft/scrollTop of the wrapper element (or container in CSS mode).
3. Restoring scroll position: We restore the saved scroll position immediately and repeatedly using requestAnimationFrame to catch any browser scroll that occurs during the focus event.
4. Scroll event listener: Added a passive scroll event listener that restores the scroll position if the browser attempts to scroll during the restoration window (100ms).
5. Slide navigation: If the focused element is in a different slide, we navigate to that slide after ensuring the scroll position is restored.

Changes

• Modified src/modules/a11y/a11y.mjs:
  • Added scroll restoration state variables (savedScrollLeft, savedScrollTop, isRestoringScroll, scrollRestoreTimeout)
  • Created restoreScrollPosition() function to restore saved scroll positions
  • Created handleScroll() function to catch and restore scroll during focus events
  • Updated handleFocusIn() to save and restore scroll position for all focusable elements
  • Added scroll event listeners in init() and cleanup in destroy()
• Added test demo: demos/4006-tab-focus-fix.html to verify the fix works correctly

Related Issues

Fixes #4006