add(); addClass(); 添加class
    remove(); removeClass();移除class

    1. <!DOCTYPE html>
    2. <html lang="en">
    3. <head>
    4.     <meta charset="UTF-8">
    5.     <meta name="viewport" content="width=device-width, initial-scale=1.0">
    6.     <title>Document</title>
    7.     <style>
    8.         .current{
    9.             color:red;
    10.         }
    11.     </style>
    12. </head>
    13. <body>
    14.     <!-- 
    15.         add();  addClass();
    16.         remove();  removeClass();
    17.      -->
    18.     <p id="app">hello world</p>
    19.     <button id="btn">移除class</button>
    20.     <script>
    21.         var app = document.getElementById("app");
    22.         var btn =  document.getElementById("btn");
    23.         app.onclick = function(){
    24.             this.classList.add("current")
    25.         }
    26.         btn.onclick =  function(){
    27.             app.classList.remove("current")
    28.         }
    29.     </script>
    31. </body>
    32. </html>

    1.PNG