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;  

}