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<!doctype html>
<meta charset="utf-8">
<link rel="help" href="https://html.spec.whatwg.org/#event-loop-processing-model">
<link rel="help" href="https://issues.chromium.org/issues/397737222">
<meta name="viewport" content="width=device-width,initial-scale=1">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
</style>
<iframe width="300" height="300" srcdoc="
<style>
html {
transition: color 1s step-start;
}
.scroller {
overflow: auto;
width: 100%;
height: 100px;
}
.spacer {
height: 500px;
}
</style>
<div class='scroller'>
<div class='spacer'></div>
</div>
<div class='scroller'>
<div class='spacer'></div>
</div>
"></iframe>
<script>
promise_test(async function() {
await new Promise(resolve => window.addEventListener("load", resolve, { once: true }));
const iframe = document.querySelector("iframe");
const mql = iframe.contentWindow.matchMedia("(max-width: 300px)");
assert_true(mql.matches, "");
// Set up a MQL change event listener to receive the event in between
// scroll and transitionrun events.
let timeOnMQLChange = null;
iframe.width = "400";
const mqlChangeEvent = new Promise(resolve => {
mql.addEventListener("change", () => {
timeOnMQLChange = performance.now();
resolve();
}, { once: true });
});
// There are two scroll containers, setup a scroll event listener for one
// of them.
const scrollers = iframe.contentDocument.querySelectorAll(".scroller");
let timeOnScrollEventOnAnotherScroller = null;
scrollers[1].addEventListener("scroll", () => {
timeOnScrollEventOnAnotherScroller = performance.now();
}, { once: true });
// Setup another scroll event listener for the other scroll container.
const scrollEventPromise = new Promise(resolve => {
scrollers[0].addEventListener("scroll", resolve, { once: true });
});
// And scroll the scroller.
scrollers[0].scrollTop = 10;
// Await the scroll event.
await scrollEventPromise;
const timeOnScrollEvent = performance.now();
// Scroll the other scroller.
scrollers[1].scrollTop = 10;
assert_equals(timeOnScrollEventOnAnotherScroller, null,
"The new scroll event should not yet have been dispatched");
// Trigger a CSS transition.
let timeOnTransitionRun = null;
const transitionrunEventPromise = new Promise(resolve => {
iframe.contentDocument.documentElement.addEventListener("transitionrun", () => {
timeOnTransitionRun = performance.now();
resolve();
}, { once: true });
});
iframe.contentDocument.documentElement.style.color = "blue";
getComputedStyle(iframe.contentDocument.documentElement).color;
// Now it's time to receive the MQL change event.
await mqlChangeEvent;
assert_less_than(timeOnScrollEvent, timeOnMQLChange,
"The MQL change event should have been dispatched after the first scroll event");
assert_equals(timeOnScrollEventOnAnotherScroller, null,
"The new scroll event should not yet have been dispatched");
// Await the transitionrun event.
await transitionrunEventPromise;
assert_less_than(timeOnScrollEvent, timeOnTransitionRun,
"The transitionrun event should have been dispatched after the first scroll event");
assert_equals(timeOnScrollEventOnAnotherScroller, null,
"The new scroll event should not yet have been dispatched");
// Await a requestAnimationFrame callback.
await new Promise(resolve => requestAnimationFrame(resolve));
assert_equals(timeOnScrollEventOnAnotherScroller, null,
"The new scroll event should not yet have been dispatched");
// Await one more requestAnimationFrame callback.
await new Promise(resolve => requestAnimationFrame(resolve));
assert_not_equals(timeOnScrollEventOnAnotherScroller, null,
"The new scroll event should now have been dispatched");
assert_less_than(timeOnTransitionRun, timeOnScrollEventOnAnotherScroller,
"The new scroll event should have been dispatched after the transitionrun event");
});
</script>
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