获取元素offsetLeft值

function offsetTop( elements ){
var top = elements.offsetTop;
var parent = elements.offsetParent;
while( parent != null ){
top += parent.offsetTop;
parent = parent.offsetParent;
};
return top;
};

 function getTop(e){

var offset=e.offsetTop;

if(e.offsetParent!=null)

offset+=getTop(e.offsetParent);

return offset;

}

element.getBoundingClientRect()   获取元素距页面顶端距离。