获取元素在页面的绝对位置

以下是代码片段：

var getCoords = function (el) {
    var box = el.getBoundingClientRect(),
        doc = el.ownerDocument,
        body = doc.body,
        html = doc.documentElement,
        clientTop = html.clientTop || body.clientTop || 0,
        clientLeft = html.clientLeft || body.clientLeft || 0,
        top = box.top + (self.pageYOffset || html.scrollTop || body.scrollTop) - clientTop,
        left = box.left + (self.pageXOffset || html.scrollLeft || body.scrollLeft) - clientLeft;
    return { 'top': top, 'left': left };
};