Adding div element to body or document in JavaScript

Using Javascript

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

Using jQuery

$('body').append('<div style="position:absolute;width:100%;height:100%;opacity:0.3;z-index:100;background:#000;"></div>');