用javascript如何给span赋值呢？一般有两种方法：
1>输出html
<body onload="s()">
<span id="hello"></span>
<script language="javascript">
function s(){
document.getElementById("hello").innerHTML = "<iframe src= height=400 width=300></iframe>";
}
</script>
2>输出文本
<body onload="s()">
<span id="hello"></span>
<script language="javascript">
function s(){
document.getElementById("hello").innerText = "hello world";
}
</script>