Have a look at jQuery 'load' :

<https://github.com/jquery/jquery/blob/main/src/ajax/load.js>

Then at the vanilla JS 'load' :

  const response = await fetch('/path/to/template.html');
  const body = await response.text();
  document.querySelector('#some.selector').innerHTML = body;

IDK, all in all it is a proxy functions lib.