[cyber]

var box = elem.getBoundingClientRect();

полный вариант

var Obj = {
	
  positX : function (elem){
	
	 var body, html, scrollX, scrollY, box, x = 0, y = 0;	
	 
      box = elem.getBoundingClientRect();
	 
      body = document.body;
		
      html = document.documentElement;
		scrollX = window.pageXOffset || html.scrollLeft || body && body.scrollLeft  || 0;
		
		scrollX = html.scrollLeft || body && body.scrollLeft || 0;
		
		
		
		
		x = box.left + scrollX - (html.clientLeft || body.sclientLeft || 0);
		
	
	return Math.round(x);
	},
	
	positY : function (elem){
	
       var body, html, scrollX, scrollY, box, x = 0, y = 0;	
	  
      box = elem.getBoundingClientRect();
	    body = document.body;
		  html = document.documentElement;
		
		scrollY = window.pageYOffset || html.scrollTop || body && body.scrollTop || 0;
	
		scrollY = html.scrollTop || body && body.scrollTop || 0;
		
		y = box.top + scrollY - (html.clientTop || body.sclientTop || 0);
		
		
		
	
	return Math.round(y);
      
	}
};