js 添加删除替换class 类

<div id="box"></div>function $(id){    return document.getElementById(id);}var box = $('box');var classVal = box.getAttribute('class');//删除类classVal = classVal.replace("someClassName","");    box.setAttribute("class",classVal );//添加类classVal = classVal.concat("someClassName");    box.setAttribute("class",classVal );//替换类classVal = classVal.replace("someClassName","otherClassName");    box.setAttribute("class",classVal );