Answers for "document append to html"

javascript append to document

var elem = document.createElement('div');
elem.style.cssText = 'position:absolute;width:100%;height:100%;opacity:0.3;z-index:100;background:#000';
document.body.appendChild(elem);

JavaScript append HTML

let app = document.querySelector('#app');
app.append('append() Text Demo');

console.log(app.textContent);