//code from http://caibaojian.com/iframe-adjust-content-height.html
<iframe src="backtop.html" frameborder="0" scrolling="no" id="test" onload="this.height=100"></iframe>
<script type="text/javascript">
function reinitIframe(){

var iframe = document.getElementById("test");

iframe.height = 0; //只有先設定原來的iframe高度為0，之前的iframe高度才不會對現在的設定有影響
try{
var bHeight = iframe.contentWindow.document.body.scrollHeight;
var dHeight = iframe.contentWindow.document.documentElement.scrollHeight;
var height = Math.max(bHeight, dHeight);
iframe.height = height;
console.log(height);
}catch (ex){}
}
window.setInterval("reinitIframe()", 200);
</script>