[Webkit-unassigned] [Bug 237912] New: STP 141: instanceof value wrong in MutationObserver callback for Safari extensions

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Tue Mar 15 11:42:12 PDT 2022


https://bugs.webkit.org/show_bug.cgi?id=237912

            Bug ID: 237912
           Summary: STP 141: instanceof value wrong in MutationObserver
                    callback for Safari extensions
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Mac (Intel)
                OS: macOS 11
            Status: NEW
          Severity: Blocker
          Priority: P2
         Component: New Bugs
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: opendarwin at lapcatsoftware.com

Created attachment 454735

  --> https://bugs.webkit.org/attachment.cgi?id=454735&action=review

Sample Xcode project

This bug occurs with Safari Technology Release 141 (Safari 15.4, WebKit 16614.1.3.7) on macOS 11.6.5. The bug does not occur with Safari 15.3 or Safari 15.4 (released yesterday), only with Safari Technology Preview.

The bug is that JavaScript instanceof is returning false when it should return true in the callback of MutationObserver for Safari extensions, both Safari web extensions and Safari app extensions. This bug does not seem to affect scripts in the web pages, only extension scripts.

Attached is a sample Safari web extension Xcode project that demonstrates the bug. Just enable the extension, run it on any web site, such as cnn.com, and look at the console log. For HTML <div> elements, it should log true true for instanceof HTMLElement and instanceof HTMLDivElement, but it logs false false in Safari Technology Preview 141.

This bug is a massive problem for me, a showstopper for several of my Safari extensions in the App Store. It totally breaks essential functionality in my extensions.

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