<!doctype html> <meta charset="utf-8"> <link rel="help" href="https://drafts.csswg.org/css-transitions/#starting"> <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1816672"> <link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io"> <link rel="author" title="Mozilla" href="https://mozilla.org"> <script src="/resources/testharness.js"></script> <script src="/resources/testharnessreport.js"></script> <iframe></iframe> <script> let t = async_test("Transitions don't incorrectly start on dynamic document element insertion"); window.onload = t.step_func_done(function() { let frame = document.querySelector("iframe"); let doc = frame.contentDocument; doc.open(); doc.write("<!doctype html>"); let root = doc.createElement("html"); root.innerHTML = ` <style> div { width: 100px; height: 100px; background-color: blue; transition: margin-left 10s ease; margin-left: 100px; } </style> <div></div> `; doc.appendChild(root); doc.close(); assert_equals(frame.contentWindow.getComputedStyle(doc.querySelector("div")).marginLeft, "100px", "Transition shouldn't have started"); }); </script>