I think this is the proper way of creating HTMLCollection, which is handled by the browser.
var docFragment = document.createDocumentFragment();
docFragment.appendChild(node1);
docFragment.appendChild(node2);
var myHTMLCollection = docFragment.children;
Refs.:
https://stackoverflow.com/a/35969890/10018427
https://developer.mozilla.org/en-US/docs/Web/API/NodeList
https://developer.mozilla.org/en-US/docs/Web/API/HTMLCollection