gistfile1.html

<link rel="preload" href="/a.js" type="application/javascript" class="core">
<link rel="preload" href="/b.js" type="application/javascript" class="cms-1-preload">
<link rel="preload" href="/c.js" type="application/javascript" class="cms-2-preloads">
<link rel="preload" href="/d.js" type="application/javascript" class="cms-2-preloads">
<script type="module" name="load-core">
  var corePromise;

  export default function() {
    if (!corePromise) {
      corePromise = document.querySelector('.core').loaded().then(function(link) {
        var script = document.createElement('script');
        script.src = link.href;
        document.head.appendChild(script);
      });
    }
    return corePromise;
  };
</script>

<!-- CMS plugin 1 -->
<script type="module">
  import loadCore from "load-core";

  document.ready(function() {
    document.querySelector('.button').addEventListener('click', function(event) {
      loadCore().then(function() {
        var link = document.querySelector('.cms-1-preload');
        var script = document.createElement('script');
        script.src = link.href;
        document.head.appendChild(script);
      });
      event.preventDefault();
    });
  });
</script>

<!-- CMS plugin 2 -->
<script type="module">
  import loadCore from "load-core";

  loadCore().then(function() {
    Array.from(document.querySelectorAll('.cms-2-preloads')).reduce(function(chain, link) {
      return chain.then(function() {
        var script = document.createElement('script');
        script.src = link.href;
        document.head.appendChild(script);
        return script.loaded();
      });
    }, Promise.resolve());
  });
</script>