printDOM function: this is very simple!

<script>

    function printDOM(node, prefix) {
        if (node.nodeName != "#text") {
            console.log(prefix + node.nodeName);
        }
        ;for (let i = 0; i < node.childNodes.length; i++) {
            printDOM(node.childNodes[i], prefix + "-->");
        }

    }
  printDOM(document,"")
</script>