how to get element by id and append 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: JavaScript append text to div

var div = document.getElementById('myElementID');
div.innerHTML += "Here is some more data appended";