[Webkit-unassigned] [Bug 161291] New: Promise chain no longer prevent UI refresh

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=161291

            Bug ID: 161291
           Summary: Promise chain no longer prevent UI refresh
    Classification: Unclassified
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: All
                OS: All
            Status: NEW
          Severity: Critical
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mpcteam.kvet at gmail.com

In Safari 10, Safari Technology Preview and Webkit Nightly Build behavour of native Promise object changed from that one in Safari 9.

Now during microtasks execution there are unnecessary UI updates. This change can break existing codebase because all (latest Chrome, FireFox, IE, Edge) browsers that support Promise object behaves correctly. Even promise polyfill in checked browsers (IE9, Android 4 Browser) works correctly. I assume that this is very critical bug in Safari 10 that breaks down compatibility with another browsers.

Issue can be reproduced in https://jsfiddle.net/Lo7utx4s/ . Clicking on 'TEST PROMISE BEHAVIOR' should not cause blue rectangle blinks with white or black.

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