The Document.body property represents the <body> or <frameset> node of the current document, or null if no such element exists.
One of the following:
// Given this HTML: <body id="oldBodyElement"></body>
alert(document.body.id); // "oldBodyElement"
const newBodyElement = document.createElement("body");
newBodyElement.id = "newBodyElement";
document.body = newBodyElement;
alert(document.body.id); // "newBodyElement"document.body is the element that contains the content for the document. In documents with <body> contents, returns the <body> element, and in frameset documents, this returns the outermost <frameset> element.
Though the body property is settable, setting a new body on a document will effectively remove all the current children of the existing <body> element.