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+<!doctype html>
+<html>
+<head>
+<meta charset=utf-8>
+<title>CSS Transitions Test: behavior when transition-timing-function changes while transitioning</title>
+<meta name="assert" content="Checks a change to the transition-timing-function
+property does not affect an in-flight transition">
+<link rel="help" title="3. Starting of transitions" href="https://drafts.csswg.org/css-transitions/#starting">
+
+<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>
+
+</head>
+<body>
+<div id="log"></div>
+
+<script>
+promise_test(async t => {
+  // Start a transition 50% of the way through with a linear timing function
+  const div = addDiv(t, {
+    style: 'transition: height 100s -50s linear; height: 0px',
+  });
+  getComputedStyle(div).height;
+  div.style.height = '100px';
+  assert_equals(
+    getComputedStyle(div).height,
+    '50px',
+    'Transition should be initially 50% complete'
+  );
+
+  // Update the timing function
+  div.style.transitionTimingFunction = 'steps(1, end)';
+
+  // If the change to the transition-timing-function was reflected, the
+  // computed height would now be '0px'.
+  assert_equals(
+    getComputedStyle(div).height,
+    '50px',
+    'Even after updating the transition-timing-function, the transition should be 50% complete'
+  );
+
+  // Wait a frame just to be sure that the changed timing function is not later
+  // updated.
+  await waitForFrame();
+
+  assert_greater_than_equal(
+    parseInt(getComputedStyle(div).height),
+    50,
+    'Even in the next frame the updated transition-timing-function should not apply'
+  );
+}, 'Changes to transition-timing-function should not affect in-flight transitions');
+</script>
+
+</body>
+</html>