<pre id="results"></pre>
<div id="target" style="width: 100px; height: 100px; background-color: black;"></div>
<script>

const opacityAnimation = new Animation(new KeyframeEffect(document.getElementById("target"), [
    { opacity: 1 },
    { opacity: 0 }
]));
opacityAnimation.startTime = 0;
opacityAnimation.effect.timing.duration = 1000;

const widthAnimation = new Animation(new KeyframeEffect(document.getElementById("target"), [
    { width: "100px" },
    { width: "200px" }
]));
widthAnimation.startTime = 0;
widthAnimation.effect.timing.duration = 1000;

testRunner.dumpAsText();
document.getElementById("results").innerText = internals.layerTreeAsText(document);

</script>