appent element to document js 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: how to appendChild in the begin of the div javascript

var element = document.getElementById("div1");
element.insertBefore(para, element.firstChild);