[cyber]

function getComputed (obj){
	  
	  try{ 
	   return getComputedStyle(obj, null)
	   
	   } catch(e){ 
	      
		  return obj.currentStyle;
		   }
		
		};

или

function getComputed (obj){
    if ( obj.ownerDocument && obj.ownerDocument.defaultView ) {
        return obj.ownerDocument.defaultView.getComputedStyle( obj, null );
    } else if ( obj.currentStyle ) {
        return obj.currentStyle;
    }
    return null;
}