js append to document body code example

Example 1: add element to body javascript

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);

Example 2: add a child html object to another html object in js

//Add child at end of object children list
parent.append(child);
//Add child at start of object children list
parent.insertBefore(child, list.childNodes[0]);