js获取计算的样式(非行间样式)

 function getStyle(obj, attr){
     if(obj.currentStyle){
         style = obj.currentStyle[attr]; //兼容IE8以下
     }else{
         style = getComputedStyle(obj,false)[attr];
     };
     return style;
 }

 var ele = document.querySelector('body');
 getStyle(ele,'width')