怎么让div始终居中浏览器可视范围的中间位置

代码：



弹出层

有个定位的属性你设置下就可以了,名称是position,有三个属性值fixed,absolute,relative
fixed是浮动,absolute是绝对定位,relative是相对定位.
自己加上这属性再每个值设置过去体会一下就知道了.

自己体会一下吧。

#mydiv {
background-color: #FFCC66;
border: 1px solid #f00;
text-align: center;
line-height: 40px;
font-size: 12px;
font-weight: bold;
z-index:99;
width: 300px;
height: 120px;
left:50%;/*FF IE7*/
top:50%;/*FF IE7*/

margin-left:-150px!important;/*FF IE7 该值为本身宽的一半 */
margin-top:-60px!important;/*FF IE7 该值为本身高的一半*/

margin-top:0px;

position:fixed!important;/*FF IE7*/
position:absolute;/*IE6*/

_top: expression(eval(document.compatMode &&
document.compatMode=='CSS1Compat') ?
documentElement.scrollTop + (document.documentElement.clientHeight-this.offsetHeight)/2 :/*IE6*/
document.body.scrollTop + (document.body.clientHeight - this.clientHeight)/2);/*IE5 IE5.5*/

}

在div外加一个表格，按照表格的形式来实现居中是最好的办法

代码：
type="text/javascript">
var
docEle
=
function()
{
return
document.getElementById(arguments[0])
||
false;
}
function
openNewDiv(_id)
{
var
m
=
"mask";
if
(docEle(_id))
document.body.removeChild(docEle(_id));
if
(docEle(m))
document.body.removeChild(docEle(m));
//mask遮罩层
var
newMask
=
document.createElement("div");
newMask.id
=
m;
newMask.style.position
=
"absolute";
newMask.style.zIndex
=
"1";
_scrollWidth
=
Math.max(document.body.scrollWidth,document.documentElement.scrollWidth);
_scrollHeight
=
Math.max(document.body.scrollHeight,document.documentElement.scrollHeight);
newMask.style.width
=
_scrollWidth
+
"px";
newMask.style.height
=
_scrollHeight
+
"px";
newMask.style.top
=
"0px";
newMask.style.left
=
"0px";
newMask.style.background
=
"#33393C";
newMask.style.filter
=
"alpha(opacity=40)";
newMask.style.opacity
=
"0.40";
document.body.appendChild(newMask);
//新弹出层
var
newDiv
=
document.createElement("div");
newDiv.id
=
_id;
newDiv.style.position
=
"absolute";
newDiv.style.zIndex
=
"9999";
newDivWidth
=
400;
newDivHeight
=
200;
newDiv.style.width
=
newDivWidth
+
"px";
newDiv.style.height
=
newDivHeight
+
"px";
newDiv.style.top
=
(document.body.scrollTop
+
document.body.clientHeight/2
-
newDivHeight/2)
+
"px";
newDiv.style.left
=
(document.body.scrollLeft
+
document.body.clientWidth/2
-
newDivWidth/2)
+
"px";
newDiv.style.background
=
"#EFEFEF";
newDiv.style.border
=
"1px
solid
#860001";
newDiv.style.padding
=
"5px";
newDiv.innerHTML
=
"
";
document.body.appendChild(newDiv);
//弹出层滚动居中
function
newDivCenter()
{
newDiv.style.top
=
(document.body.scrollTop
+
document.body.clientHeight/2
-
newDivHeight/2)
+
"px";
newDiv.style.left
=
(document.body.scrollLeft
+
document.body.clientWidth/2
-
newDivWidth/2)
+
"px";
}
if(document.all)
{
window.attachEvent("onscroll",newDivCenter);
}
else
{
window.addEventListener('scroll',newDivCenter,false);
}
//关闭新图层和mask遮罩层
var
newA
=
document.createElement("div");
newA.innerHTML
="取消";
var
newB
=
document.createElement("TEXTAREA");
newB.setAttribute("cols","40");
newB.setAttribute("rows","10");
newA.onclick
=
function(){
if(document.all)
{
window.detachEvent("onscroll",newDivCenter);
}
else
{
window.removeEventListener('scroll',newDivCenter,false);
}
document.body.removeChild(docEle(_id));
document.body.removeChild(docEle(m));
return
false;
}
newDiv.appendChild(newB);
newDiv.appendChild(newA);
}


onclick="openNewDiv('newDiv');return
false;"
style="cursor:pointer">弹出层