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')