在页面加载完毕后，向div元素追加span子元素
<html>
<head>
<title>js</title>
<script type="text/javascript">
window.onload=function(){
var div=document.getElementById("divid");
var span=document.createElement("span");
span.id="spanid";
span.style.color="blue";
span.innerHTML=" i am append span !"
div.appendChild(span);
}
</script>
</head>
<body>
<div id="divid" style="color: red; font-size:80;">i am div !</div>
</body>
</html>