iframe通过js自动调节高度

<div class="RightSpan">
                    <iframe id="mainFrame" name="mainFrame" src="MainPage.aspx" frameborder="0" scrolling="no" style="100%;aho:expression(autoResize())"></iframe>
                </div>

定义js函数
function autoResize()
{
    try
    {
        document.all["mainFrame"].style.height = mainFrame.document.body.scrollHeight;
    }
    catch(e){}
}