<!doctype html>
<meta charset=utf-8>
<title>Transitions start at the same time regardless of on-screen status</title>
<link rel="help" href="https://drafts.csswg.org/css-animations-2/">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1888748">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
.transition {
width: 100px;
height: 100px;
background-color: blue;
transition: translate 10000ms linear;
will-change: translate;
translate: 0;
}
.offscreen {
background-color: purple;
translate: -1000px;
}
</style>
<div class="transition"></div>
<div class="transition offscreen"></div>
<script>
'use strict';
promise_test(async t => {
let [a, b] = document.querySelectorAll(".transition");
// Ensure a paint happens to make sure a transition gets triggered (otherwise
// getAnimations() would flush sync, and maybe not trigger a transition if
// it's the first style of the elements).
await new Promise(r => requestAnimationFrame(() => requestAnimationFrame(r)));
// Trigger both transitions at the same time.
a.style.translate = b.style.translate = "100px";
let ta = a.getAnimations()[0];
let tb = b.getAnimations()[0];
await Promise.all([ta.ready, tb.ready]);
assert_equals(ta.startTime, tb.startTime, "Both transitions should've started at the same time");
});
</script>
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