canvas-as-favicon.html

<link rel="shortcut icon" width=32px>
<canvas style="display: none" id="loader" width="16" height="16"></canvas>

<script>
class Loader {
  constructor(link, canvas) {
    this.link = link;
    this.canvas = canvas;
    this.context = canvas.getContext('2d');
    this.context.lineWidth = 2;
    this.context.strokeStyle = "white";
  }
  setProgress(progress) {
    const startAngle = 1.5 * Math.PI;
    this.context.clearRect(0, 0, 16, 16);
    this.context.beginPath();
    this.context.arc(8, 8, 5, startAngle, (progress * 2 * Math.PI) / 100 + startAngle);
    this.context.stroke();
    this.link.href = this.canvas.toDataURL("image/png"); // update favicon
  }
}

const canvas = document.querySelector("#loader");
const link = document.querySelector('link[rel*="icon"]');
const loader = new Loader(link, canvas);

let progress = 0;
const loading = () => {
  loader.setProgress(progress);
  if (progress >= 100) {
    return;
  }
  progress++;
  requestAnimationFrame(loading);
}
loading();
</script>