动态添加元素

封装好的方法：
//创建标签
var paraElement = document.getElementsByTagName("body")[0]; //父标签
function creatElement(idName,className,eleName,nodeText){
var element = document.createElement(eleName);
var node = document.createTextNode(nodeText);
element.setAttribute("id",idName);
element.className = className;
element.appendChild(node);
paraElement.appendChild(element);
}
creatElement("xiao","ge","div","新创建的标签");