原生js判断是否有某个class，如果有就删掉，没有加上

 <style>
     #div1 {
         width: 100px;
         height: 100px;
         position: absolute;
     }

     .div1 {
         background: red;
     }

     .div2 {
         background: yellow;
     }
 </style>

 <div id="div1" class="div2 div1 div3 div2"></div>

 <script>
     var oDiv1 = document.getElementById("div1");

     oDiv1.onclick = function() {
         switchClass(this, "div2")
     }

     function switchClass(obj, sClass) {
         var oldClass = obj.className;
         var re = new RegExp('\\b' + sClass + '\\b');
         if (re.test(oldClass)) {
             obj.className = obj.className.split(sClass).join("").replace(/\s+$/, "")
         } else {
             obj.className = oldClass + " " + sClass
         }
     }
 </script>