Question

<body>
   <button class="openNav" onclick="toggleSideBar()"><i class="fas fa-bars"></i> 
  </button>
   <nav>
      <a href="#">Home</a>
      <a href="#">About</a>
      <a href="#">The Team</a>
      <a href="#">Contact</a>
   </nav>
   <div id="sidebar">
    <ul>
    <li>cat1</li>
    <li>cat1</li>
    <li>cat1</li>
    <li>cat1</li>
    </ul>
   </div>

   </body>
    <script src="resources/javascript/main.js"></script>
    <script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"> 
   </script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js"> 
   </script>

   <script>
     function toggleSideBar(){
      console.log("inside toggleland");
      document.getElementById("sideBar").classList.toggle('active');
     }
   </script>

无法运行此代码。出现了JavaScript错误“未捕获的TypeError：无法读取HTMLButtonElement.onclick上toggleSideBar处的null属性'classList'> null”

Answer 1

在sideBar中用sidebar替换getElementById。您没有ID为sideBar的元素。

Answer 2

id为<?xml version="1.0" encoding="utf-8"?> <set xmlns:android="http://schemas.android.com/apk/res/android"> <alpha android:fromAlpha="1.0" android:toAlpha="1.0" android:duration="250" /> </set>，而您选择的驼峰ID为sidebar，请尝试sideBar

未捕获的TypeError：切换html元素时无法读取null的属性'classList'

2 个答案: