PerformanceTests/CSS/FontFaceSetUpdateStyle.html

<!DOCTYPE html>
<html>
<head id="head">
<script src="../resources/runner.js"></script>
<style id="style">
</style>
</head>
<body id="body">
<div id="test"></div>
</body>
<script>
let head = document.getElementById("head");
let style = document.getElementById("style");
let body = document.getElementById("body");
let styleString = "";
let elementCount = 1000;
for (let i = 0; i < elementCount; ++i) {
    let div = document.createElement("div");
    let id = `div${i}`;
    div.id = id;
    body.appendChild(div);
    styleString = styleString + `#${id} { font-weight: ${i}; }`;
}
style.innerText = styleString;
PerfTestRunner.measureRunsPerSecond({run:function() {
    style.innerText = `${styleString}`;
    let fontFace = new FontFace("WebFont", "url('MyCoolWebFont.ttf') format('truetype')");
    if (!document.fonts.has(fontFace))
        document.fonts.add(fontFace)
    document.fonts.clear();
}});
</script>
</html>