Answers for "append html to parent javascript"

js append element to body

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 element to parent

let parent = document.body;
let childToAppend = document.createElement('a');

parent.appendChild(childToAppend)