[Webkit-unassigned] [Bug 245147] New: Safari 16 regression: CSS animations stutter during DOM mutation

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=245147

            Bug ID: 245147
           Summary: Safari 16 regression: CSS animations stutter during
                    DOM mutation
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: All
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Animations
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: alex at harding.dev
                CC: dino at apple.com, graouts at apple.com

Reproduction:

https://codepen.io/aeharding/pen/poVEmWO

After clicking "Do an intensive task", you will see the spinner stops momentarily/stutter.

This regression started occurring after upgrading to Safari 16 (both iOS 16 and m1 macbook air running macOS 12.6) yesterday.

When I test on an older iOS (15) version, an older macOS version (12.2 tested on a different macbook air m1), Chrome or Firefox or iPadOS, the CSS animation does not stutter at all.

This is a problem for any website that has a loading indicator while rendering a large amount of content to the DOM.

This is also occurring on Safari Technology Preview 153 with macOS 12.6.

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