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<!doctype html>
<html>
<head>
<meta charset=utf-8>
<title>CSS Transitions Test: transition of a custom property with "transition-behavior: allows-discrete"</title>
<meta name="assert" content="Checks that transitioning a custom property with 'transition-behavior: allows-discrete' works as expected">
<link rel="help" href="https://drafts.csswg.org/css-transitions-2/#transition-behavior-property">
<script src="/resources/testharness.js" type="text/javascript"></script>
<script src="/resources/testharnessreport.js" type="text/javascript"></script>
<script src="./support/helper.js" type="text/javascript"></script>
<style>
.target {
transition: --foo 10s step-start;
transition-behavior: allow-discrete;
--foo: bar;
}
</style>
</head>
<body>
<div id="log"></div>
<script>
promise_test(async t => {
const div = addDiv(t, { class: 'target' });
let transitionCount = 0;
div.addEventListener("transitionstart", () => transitionCount++);
// Trigger a transition on the custom property.
getComputedStyle(div).getPropertyValue('--foo');
div.style.setProperty('--foo', 'baz');
getComputedStyle(div).getPropertyValue('--foo');
// Wait two more frames to ensure only a single transition was started.
await waitForFrame();
await waitForFrame();
assert_equals(transitionCount, 1, 'A single "transitionstart" event was dispatched');
}, 'It is possible to transition an unregistered custom property using "transition-behavior: allows-discrete"');
promise_test(async t => {
const div = addDiv(t);
div.style.setProperty('--foo', 'bar');
// Trigger a transition on the custom property.
getComputedStyle(div).getPropertyValue('--foo');
div.style.transition = "--foo 10s allow-discrete";
div.style.setProperty('--foo', 'baz');
assert_equals(div.getAnimations()[0].transitionProperty, '--foo', 'A transition was started for the custom property');
}, 'It is possible to transition an unregistered custom property using "transition-behavior: allows-discrete" when setting "transition-property" in the style change that yields the transition');
</script>
</body>
</html>
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