js各浏览器兼容取的元素的位置X坐标 Y坐标

function getElementPos(elementId)
{
var ua = navigator.userAgent.toLowerCase();
var isOpera = (ua.indexOf('opera') != -1);
var isIE = (ua.indexOf('msie') != -1 && !isOpera); // not opera spoof
var el = document.getElementById(elementId);
if(el.parentNode === null || el.style.display == 'none')
{
return false;
}

var parent = null;
var pos = [];
var box;

if(el.getBoundingClientRect) //IE
{
box = el.getBoundingClientRect();
var scrollTop = Math.max(document.documentElement.scrollTop, document.body.scrollTop);
var scrollLeft = Math.max(document.documentElement.scrollLeft, document.body.scrollLeft);
return {x:box.left + scrollLeft, y:box.top + scrollTop};
}
else if(document.getBoxObjectFor) // gecko
{
box = document.getBoxObjectFor(el);
var borderLeft = (el.style.borderLeftWidth)?parseInt(el.style.borderLeftWidth):0;
var borderTop = (el.style.borderTopWidth)?parseInt(el.style.borderTopWidth):0;
pos = ;
}
else // safari & opera
{
pos = [el.offsetLeft, el.offsetTop];
parent = el.offsetParent;

if (parent != el)
{
while (parent)
{
pos[0] += parent.offsetLeft;
pos[1] += parent.offsetTop;
parent = parent.offsetParent;
}
}

if (ua.indexOf('opera') != -1 || ( ua.indexOf('safari') != -1 && el.style.position == 'absolute' ))
{
pos[0] -= document.body.offsetLeft;
pos[1] -= document.body.offsetTop;
}
}

if (el.parentNode)
{
parent = el.parentNode;
}
else
{
parent = null;
}

while (parent && parent.tagName != 'BODY' && parent.tagName != 'HTML')
{
// account for any scrolled ancestors
pos[0] -= parent.scrollLeft;
pos[1] -= parent.scrollTop;

if (parent.parentNode)
{
parent = parent.parentNode;
}
else
{
parent = null;
}
}
return {x:pos[0], y:pos[1]};
}