div超出屏幕高度后自动出现滚动条

<script language="javascript" type="text/javascript">
     $(document).ready(function()
	{
		// 浏览器的高度和div的高度
		var height = $(window).height(); 
		var divHeight = $("#scolldiv").height();
		
		//获取div对象
		var divh = $("#scolldiv").get(0);
		
		//div高度大于屏幕高度把屏幕高度赋给div，并出现滚动条
		if (divHeight > height-20)
		{
			divh.style.height = height-20;
			divh.style.overflow = "auto";
		}
	});
 </script>
<div id="scolldiv" style="width: 100%;"><br /></div>