test.js

document.querySelectorAll('#contents_list a').forEach((v) => {
  fetch(v).
  then((response) => response.text()).
  then((txt) => {
    const parser = new DOMParser();
    const src = parser.parseFromString(txt, 'text/html');
    const mp4_url = src.querySelector('video source').src;
    const elem = document.createElement('a');
    elem.download = '';
    elem.href = mp4_url;
    document.body.appendChild(elem);
    elem.click();
  });
});