js返回顶部的代码

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 <script src="js/jquery-1.7.1.min.js" type="text/javascript"></script>




<style>
     #backToTop{ position:fixed; _position:absolute; bottom:50px; right:0; z-index:999999; display:block; }
     a.backToTop_a{  background:url(images/7_08.png) no-repeat; width:68px; height:79px; display:block; }
     a.backToTop_a:active{  background:url(images/7_11.png) no-repeat; }
</style>

<div id="backToTop">
    <a href="javascript:void(0)" onfocus="this.blur();" class="backToTop_a png"></a>
 </div>

　　　　　　<script>
                 $("#backToTop").live("click", function(){
                        var _this = $(this);
                        $('html,body').animate({ scrollTop: 0 }, 500 ,function(){
                            _this.hide();
                        });
                    });

                    $(window).scroll(function(){
                        var htmlTop = $(document).scrollTop();
                        if( htmlTop > 0){
                            $("#backToTop").show();    
                        }else{
                            $("#backToTop").hide();
                        }
                    });
            </script>