<!DOCTYPE html>
<html>
<head>
<style>

#target {
    width: 100px;
    height: 100px;
    background-color: black;
    animation-name: animation;
}

#other {
    width: 100px;
    height: 100px;
    background-color: black;
    animation: animation 0.2s infinite;
}

#target.animated {
    animation-duration: 0.2s;
	animation-iteration-count: infinite;
}

@keyframes animation {
    to { margin-left: "100px" };
}

</style>
</head>
<body>
<script src="../resources/testharness.js"></script>
<script src="../resources/testharnessreport.js"></script>
<div id="target"></div>
<div id="other"></div>

<script>

    async_test(t => {

    const once = { once: true };
    const target = document.getElementById("target");

    // Start the animation.
    target.classList.add("animated");
    target.addEventListener("animationstart", event => {
        // Now we can cancel this animation.
        target.classList.remove("animated");
        target.addEventListener("animationend", event => {
            // We wait a frame, resume the animation and check it's the same animation.
            requestAnimationFrame(() => {
                target.classList.add("animated");
                target.addEventListener("animationstart", event => t.done(), once);
            });
        }, once);
    }, once);

}, "A CSS Animation can be canceled and resumed by modifying its animation-duration.");

</script>
</body>
</html>