javascript获取元素离文档各边距离的方法

function getDistance(obj) { 
 if (!obj instanceof jQuery) { 
     obj = $(obj); 
 } 
 var distance = {}; 
 distance.top = (obj.offset().top - $(document).scrollTop()); 
 distance.bottom = ($(window).height() - distance.top - obj.outerHeight()); 
 distance.left = (obj.offset().left - $(document).scrollLeft()); 
 distance.right = ($(window).width() - distance.left - obj.outerWidth()); 
 return distance; 
}