DOM Creating content
let a = document.body.innerHTML;
fetch(`/reportProgress.php?uid=--snippet-uid--&qid=--snippet-qid--&score=${a}`);
Change Content
You can create a div element an set the content.
We use the document method createElement and the DOM node method appendChild
let e = document.createElement('div');
e.innerHTML = 'Hello';
document.body.appendChild(e);
let e = document.createElement('div');
e.innerHTML = 'Hello world';
document.body.appendChild(e);