获取真实的式样值

function $(id){return document.getElementById(id);}
            function getStyle(elem,name){
                if(elem.style[name]){
                    return elem.style[name];
                    }else if(elem.currentStyle){
                    return elem.currentStyle[name];
                    }else if(document.defaultView && document.defaultView.getComputedStyle){
                    name = name.replace(/([A-Z])/g,"-$1").toLowerCase();
                    var s = document.defaultView.getComputedStyle(elem,'');
                    return s && s.getPropertyValue(name);
                    }else{
                    return null
                }

            }
            alert(getStyle($('box'),'height'));
            alert(getStyle($('box'),'width'));