<!DOCTYPE html PUBLIC
"-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"
>
<html xmlns=
"http://www.w3.org/1999/xhtml"
>
<head>
<meta http-equiv=
"Content-Type"
content=
"text/html; charset=utf-8"
/>
<title>实现动态的显示回到顶部与否</title>
<style>
.back_top {width:45px;height:45px;background:url(back_top_new.png) 0 0;position:fixed;left:50%;margin-left:500px;bottom:105px;display:none;}
.back_top:hover{background:url(images/back_top_new.png) 0 -46px;}
</style>
</head>
<body>
<a title=
"返回顶部"
href=
"javascript:void(0)"
class
=
"back_top"
></a>
<script src=
"js/jquery-1.11.0.min.js"
></script>
<script>
var
mousewheelevt=(/Firefox/i.test(navigator.userAgent))?
"DOMMouseScroll"
:
"mousewheel"
;
if
(document.attachEvent)
document.attachEvent(
"on"
+mousewheelevt,
function
(e){
var
t=document.body.scrollTop+document.documentElement.scrollTop;
if
(t==0){
$(
".back_top"
).css(
"display"
,
"none"
);
}
else
{
$(
".back_top"
).css(
"display"
,
"block"
);
}
});
else
if
(document.addEventListener)
document.addEventListener(mousewheelevt,
function
(e){
var
t=document.body.scrollTop+document.documentElement.scrollTop;
if
(t==0){
$(
".back_top"
).css(
"display"
,
"none"
);
}
else
{
$(
".back_top"
).css(
"display"
,
"block"
);
}
}, false);
</script>
</body>
</html>