<title>jQuery实现的返回顶部功能</title>
<style>
body {height:2000px;}
#gotoTop{
	display:none;
	position:fixed;
	top:75%;
	left:50%;
	cursor:pointer;
	margin-top:-50px;
	margin-left:520px;
	width: 64px;
	height:64px;
	line-height: 100;
	overflow: hidden;
	background: url(/uploads/allimg/140902/1_1111215171.png) no-repeat;
}
#gotoTop{
	_position:absolute;
	_top:expression_r(documentElement.scrollTop + documentElement.clientHeight * 3/4 + "px");
}
</style>
<script src="http://libs.baidu.com/jquery/1.9.0/jquery.js"></script>
<script>
var min_height = 500;
$(function(){
	$(window).scroll(function(){
		//当窗口的滚动条的垂直位置大于页面的最小高度时，让返回顶部元素渐现，否则渐隐
		if($(window).scrollTop() > min_height){
			$("#gotoTop").fadeIn(100);
		}else{
			$("#gotoTop").fadeOut(200);
		}
	});
	$("#gotoTop").click(function(){
		$('html,body').animate({scrollTop:0},200);
	});
});
</script>
<p>将滚动条拖到底部</p>
<div id="gotoTop" class="hover">返回顶部</div>