Bug 238093

Summary:	preventScroll does not work with dynamically created elements
Product:	WebKit	Reporter:	Elliot Nahman <Elliot.nahman>
Component:	Forms	Assignee:	Nobody <webkit-unassigned>
Status:	NEW ---
Severity:	Normal	CC:	augus.dupin, caleb, cdumez, rik, simon.fraser, webkit-bug-importer, wenson_hsieh
Priority:	P2	Keywords:	InRadar
Version:	Safari 15
Hardware:	Mac (Intel)
OS:	macOS 11
See Also:	https://bugs.webkit.org/show_bug.cgi?id=267051

Description Elliot Nahman 2022-03-18 13:46:22 PDT

Safari 15 appears to have implemented the preventScroll option for Element.focus(). See the resolved webkit bug: https://bugs.webkit.org/show_bug.cgi?id=178583. 

While this feature works fine for elements already existing in the DOM, it does not work for dynamically added elements. 

Please see: https://codepen.io/nonmetalhail/pen/KKZzagd

Comment 1 Simon Fraser (smfr) 2022-03-18 13:52:27 PDT

Thanks for the report. I can reproduce.

Comment 2 Radar WebKit Bug Importer 2022-03-18 13:52:39 PDT

<rdar://problem/90502768>

Comment 3 Simon Fraser (smfr) 2022-03-18 14:12:36 PDT

In the bad case we're scrolling via FrameSelection::updateAppearanceAfterLayoutOrStyleChange().

Comment 4 Simon Fraser (smfr) 2022-03-18 14:17:42 PDT

Layout calls FrameSelection::setNeedsSelectionUpdate() which resets m_selectionRevealMode to SelectionRevealMode::Reveal here:

    if (innerTextSizeChanged && frame().selection().isFocusedAndActive() && document().focusedElement() == &inputElement()) {
        // The caps lock indicator was hidden or shown. If it is now visible then it may be occluding
        // the current selection (say, the caret was after the last character in the text field).
        // Schedule an update and reveal of the current selection.
        frame().selection().setNeedsSelectionUpdate(FrameSelection::RevealSelectionAfterUpdate::Forced);
    }

This is trying to ensure that text within the input is scrolled into view, but has the side effect of also triggering page scrolling.