原生js给DOM元素添加一个或者多个类名

// 覆盖原来的样式
document.getElementById("test").setAttribute("class","test1");
var dom=document.getElementsByClassName("test")[0].setAttribute("class","test1");
// 追加样式不覆盖原来的样式
document.getElementById("test").classList.add("test1");
document.getElementById("test").classList.add("test1","test2","test3");
var dom=document.getElementsByClassName("test")[0].classList.add("test1");
var dom=document.getElementsByClassName("test")[0].classList.add("test1","test2","test3");