viewof sumC = {
const div = html`<div style="background:red;width:0;height:33px;">`;
(async () => {
let sum = 0;
for (let i = 0, n = 1000; i < n; ++i) {
sum += i * i;
div.style.width = (i / n) * 100 + "%";
await new Promise(requestAnimationFrame);
}
div.value = sum;
div.dispatchEvent(new CustomEvent("input"));
div.style.background = "black";
})();
return div;
}