<pre name="code" class="css"><style>
#anchor:{
position:absulate;
top:40%;
left:40%;
width:100px;
height:100px;
background-color:red;
}
</style></pre><br>
<pre name="code" class="javascript">var auchorTop = $("#anchor").css("top");
auchorTop = Number(auchorTop.substring(0, anchorTop.indexOf("p"))); //首先在監(jiān)聽器外部記錄某id=anchor的標簽的初始位置
window.onscroll = function () {
var top = document.documentElement.scrollTop || document.body.scrollTop;
$("#anchor").css("top", anchorTop + top + "px");
};</pre>
