js 元素对象位置

　　1：获取指定元素的位置left和top

　　

        //用 Javascript 获取指定页面元素的位置
    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]};
    }  

　　调用方法：var pos = getElementPos(obj.id);

　　　　　　　　alert(pos.x + "   " + pos.y);