The Document.append() method inserts a set of Node objects or string objects after the last child of the document. String objects are inserted as equivalent Text nodes.
This method appends a child to a Document. To append to an arbitrary element in the tree, see Element.append().
append(param1)
append(param1, param2)
append(param1, param2, paramN)
If you try to append an element to an existing HTML document, it might throw a HierarchyRequestError DOMException given a <html> element already exists.
let html = document.createElement("html");
document.append(html);
If you are creating a new document without any existing element, you can append a root HTML element (or a root SVG element):
let doc = new Document();
let html = document.createElement("html");
doc.append(html);
doc.children;