获取控件元素的绝对位置|

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 = [box.x - borderLeft, box.y - borderTop];
  
} 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]};
}