<html>
    <head>
      <base href="https://bugs.webkit.org/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - Promise chain no longer prevent UI refresh"
   href="https://bugs.webkit.org/show_bug.cgi?id=161291">161291</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Promise chain no longer prevent UI refresh
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>WebKit
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>Safari Technology Preview
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>All
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>Critical
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P2
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>JavaScriptCore
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>webkit-unassigned&#64;lists.webkit.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>mpcteam.kvet&#64;gmail.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>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 <a href="https://jsfiddle.net/Lo7utx4s/">https://jsfiddle.net/Lo7utx4s/</a> . Clicking on 'TEST PROMISE BEHAVIOR' should not cause blue rectangle blinks with white or black.</pre>
        </div>
      </p>
      <hr>
      <span>You are receiving this mail because:</span>
      
      <ul>
          <li>You are the assignee for the bug.</li>
      </ul>
    </body>
</html>