function getXY(obj){
var a = new Array();
var t = obj.offsetTop;
var l = obj.offsetLeft;
var w = obj.offsetWidth;
var h = obj.offsetHeight;
while(obj=obj.offsetParent){
t+=obj.offsetTop;
l+=obj.offsetLeft;
}
a[0] = t;
a[1] = l;
a[2] = w;
a[3] = h;
return a;
}
不过这个办法的效率实在是不敢恭维，而且在兼容性上也有很大的问题。今天看yui，了解到 getBoundingClientRect这个属性，原来IE自带了这个办法可以很方便地获取到元素的位置。（对该方法的表述可见John Resig的 getBoundingClientRect is Awesome）。既而挖掘了jquery和yui中相关内容的写法。
这是jQuery中的做法：
// The Offset Method
// Originally By Brandon Aaron, part of the Dimension Plugin
// http://jquery.com/plugins/project/dimensions
jQuery.fn.offset = function() {
var left = 0, top = 0, elem = this[0], results;
if ( elem ) with ( jQuery.browser ) {
var parent = elem.parentNode,
offsetChild = elem,
offsetParent = elem.offsetParent,
doc = elem.ownerDocument,
safari2 = safari && parseInt(version) < 522 && !/adobeair/i.test(userAgent),
fixed = jQuery.css(elem, "position") == "fixed";
// Use getBoundingClientRect if available
if ( elem.getBoundingClientRect ) {
var box = elem.getBoundingClientRect();
// Add the document scroll offsets
add(box.left + Math.max(doc.documentElement.scrollLeft, doc.body.scrollLeft),
box.top + Math.max(doc.documentElement.scrollTop, doc.body.scrollTop));
// IE adds the HTML element's border, by default it is medium which is 2px
// IE 6 and 7 quirks mode the border width is overwritable by the following css html { border: 0; }
// IE 7 standards mode, the border is always 2px
// This border/offset is typically represented by the clientLeft and clientTop properties
// However, in IE6 and 7 quirks mode the clientLeft and clientTop properties are not updated when overwriting it via CSS
// Therefore this method will be off by 2px in IE while in quirksmode
add( -doc.documentElement.clientLeft, -doc.documentElement.clientTop );
// Otherwise loop through the offsetParents and parentNodes
} else {
// Initial element offsets
add( elem.offsetLeft, elem.offsetTop );
// Get parent offsets
while ( offsetParent ) {
// Add offsetParent offsets
add( offsetParent.offsetLeft, offsetParent.offsetTop );
// Mozilla and Safari > 2 does not include the border on offset parents
// However Mozilla adds the border for table or table cells
if ( mozilla && !/^t(able|d|h)$/i.test(offsetParent.tagName) || safari && !safari2 )
border( offsetParent );
// Add the document scroll offsets if position is fixed on any offsetParent
if ( !fixed && jQuery.css(offsetParent, "position") == "fixed" )
fixed = true;
// Set offsetChild to previous offsetParent unless it is the body element
offsetChild = /^body$/i.test(offsetParent.tagName) ? offsetChild : offsetParent;
// Get next offsetParent
offsetParent = offsetParent.offsetParent;
}
// Get parent scroll offsets
while ( parent && parent.tagName && !/^body|html$/i.test(parent.tagName) ) {
// Remove parent scroll UNLESS that parent is inline or a table to work around Opera inline/table scrollLeft/Top bug
if ( !/^inline|table.*$/i.test(jQuery.css(parent, "display")) )
// Subtract parent scroll offsets
add( -parent.scrollLeft, -parent.scrollTop );
// Mozilla does not add the border for a parent that has overflow != visible
if ( mozilla && jQuery.css(parent, "overflow") != "visible" )
border( parent );
// Get next parent
parent = parent.parentNode;
}
// Safari <= 2 doubles body offsets with a fixed position element/offsetParent or absolutely positioned offsetChild
// Mozilla doubles body offsets with a non-absolutely positioned offsetChild
if ( (safari2 && (fixed || jQuery.css(offsetChild, "position") == "absolute")) ||
(mozilla && jQuery.css(offsetChild, "position") != "absolute") )
add( -doc.body.offsetLeft, -doc.body.offsetTop );
// Add the document scroll offsets if position is fixed
if ( fixed )
add(Math.max(doc.documentElement.scrollLeft, doc.body.scrollLeft),
Math.max(doc.documentElement.scrollTop, doc.body.scrollTop));
}
// Return an object with top and left properties
results = { top: top, left: left };
}
这是YUI中的做法：
var getXY = function() {
if (document.documentElement.getBoundingClientRect) { // IE
return function(el) {
var box = el.getBoundingClientRect();
var rootNode = el.ownerDocument;
return [box.left + Y.Dom.getDocumentScrollLeft(rootNode), box.top +
Y.Dom.getDocumentScrollTop(rootNode)];
};
} else {
return function(el) { // manually calculate by crawling up offsetParents
var pos = [el.offsetLeft, el.offsetTop];
var parentNode = el.offsetParent;
// safari: subtract body offsets if el is abs (or any offsetParent), unless body is offsetParent
var accountForBody = (isSafari &&
Y.Dom.getStyle(el, 'position') == 'absolute' &&
el.offsetParent == el.ownerDocument.body);
if (parentNode != el) {
while (parentNode) {
pos[0] += parentNode.offsetLeft;
pos[1] += parentNode.offsetTop;
if (!accountForBody && isSafari &&
Y.Dom.getStyle(parentNode,'position') == 'absolute' ) {
accountForBody = true;
}
parentNode = parentNode.offsetParent;
}
}
if (accountForBody) { //safari doubles in this case
pos[0] -= el.ownerDocument.body.offsetLeft;
pos[1] -= el.ownerDocument.body.offsetTop;
}
parentNode = el.parentNode;
// account for any scrolled ancestors
while ( parentNode.tagName && !patterns.ROOT_TAG.test(parentNode.tagName) )
{
if (parentNode.scrollTop || parentNode.scrollLeft) {
// work around opera inline/table scrollLeft/Top bug (false reports offset as scroll)
if (!patterns.OP_SCROLL.test(Y.Dom.getStyle(parentNode, 'display'))) {
if (!isOpera || Y.Dom.getStyle(parentNode, 'overflow') !== 'visible') { // opera inline-block misreports when visible
pos[0] -= parentNode.scrollLeft;
pos[1] -= parentNode.scrollTop;
}
}
}
parentNode = parentNode.parentNode;
}
return pos;
};
}
}()
不错的，代码就不解读了，收藏ing……
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