svg-favicons-polyfill.js

if (!window.OffscreenCanvas) {
  window.OffscreenCanvas = class OffscreenCanvas {
    constructor(width, height) {
      this.canvas = document.createElement("canvas");
      this.canvas.width = width;
      this.canvas.height = height;

      this.canvas.convertToBlob = () => {
        return new Promise(resolve => {
          this.canvas.toBlob(resolve);
        });
      };

      return this.canvas;
    }
  };
}

function loadImage(url){
return new Promise((resolve)=>{
let i=new Image();
i.onload=()=>resolve(i);
i.src=url
})
}

(async()=>{
let favicon=document.querySelector('link[rel="shortcut icon"][href*="svg"]')
let i=await loadImage(favicon.href)
let c=new OffscreenCanvas(512,512)
let ctx=c.getContext("2d")
ctx.drawImage(i,0,0,512,512)
favicon.href=URL.createObjectURL(await c.convertToBlob())
})();