切换图增加一个class

怎么判断class=“one ”里面是否有这个active。
如果有的话在class=“head”在增加一个类名on
如果没有就消失。

下面这个是banner图切换效果，就是切换到第一张class="one" 有active的时候就在head增加这个类名on


<div class="head"></div>
<div class="banner">
     <div class="slide one active"></div>
     <div class="slide"></div>
     <div class="slide"></div>
</div>



var active= document.querySelector('.active');
   var head= document.querySelector('.head');
   var res = div2.getAttribute('class');
   if(res .indexOf('active') > -1){
       head.classList.add("on");
   }else{
       res .classList.remove("active");
   }

这样就可以了哦，有问题继续沟通
望采纳 ^.^ 谢谢啦~

 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
   
</style>
<body>
        <div class="head"></div>
        <div class="banner">
             <div class="slide one active">1</div>
             <div class="slide two">2</div>
             <div class="slide three">3</div>
        </div>

<script>
    var head = document.querySelector('.head');
    var one = document.querySelector('.one');
    var two = document.querySelector('.two');
    var three = document.querySelector('.three');
    var slide = document.querySelector('.slide');
    one.onclick = function() {
        one.classList.add("active");
        head.classList.add("on");
    }
    two.onclick = function() {
        one.classList.remove("active");
        change()
    }
    three.onclick = function() {
        one.classList.remove("active");
        change()
    }
   //判断的方法，也就是切换banner触发的
    change = function(){
        var oneclass = one.getAttribute('class');
        if(oneclass.indexOf('active') > -1){
            head.classList.add("on");
        }else{
            head.classList.remove("on");
        }
    }
    

</script>
</body>
</html>

你用的swiper哪个版本？