const elementOnPage = (arg: HTMLElement | null): HTMLElement => {
  let tried = arg;
  while (tried === null) {
    // debugger;
    console.log("nothing yet");
    tried = arg;
  }
  return tried;
};

...
await elementOnPage(
        dom.window.document.querySelector("#some element that I know will eventually be loaded onto the page")
      );
...

dom.window.document.getElementsByClassName("some class that will eventually have member elements")