a try I did..

offscreen_in_worker.ts

function renderImage(ctx, url, width, height): Promise<boolean> {
  return new Promise((resolve) => {
    fetch(url)
      .then((res) => res.blob())
      .then((blob) => createImageBitmap(blob))
      .then((ibm) => {
        ctx.drawImage(ibm, 0, 0);
        resolve();
      });
  });
}




export class InlineWorkerHelper {
  /**
   * Inline worker workaround of running web workers from within an Angular lib
   * Returns an instance of the worker
   */
  static run(task: (ctx, url, width, height) => Promise<boolean>, offscreen: any, imgUrl, width, height): Worker {
    // if (!(usrCode instanceof Function)) {
    //   return;
    // }
    const code = `const renderImage = ${task};
    self.onmessage = ({ data }) => {
       if (data.id !== 'export_png') { return; }
      renderImage(data.canvas.context, data.imgUrl, data.width, data.height).then(result => self.postMessage(result, null))
  };`;

    const blob = new Blob([code], { type: 'application/javascript' });
    const url = URL.createObjectURL(blob);
    const worker = new Worker(url);
    worker.postMessage(
      { id: 'export_png', action: 'init', canvas: offscreen, imgUrl, width, height },
      [offscreen] // the transformed canvas
    );
    return worker;
  }
}