js二级导航菜单源码

以下是一个简单的 JavaScript 二级导航菜单的源码示例：

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>二级导航菜单</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      list-style: none;
    }

    .nav {
      display: flex;
      background-color: #333;
    }

    .nav>li {
      position: relative;
    }

    .nav>li>a {
      display: block;
      padding: 10px 20px;
      color: #fff;
      text-decoration: none;
    }

    .nav>li>a:hover {
      background-color: #555;
    }

    .sub-menu {
      display: none;
      position: absolute;
      top: 100%;
      left: 0;
      background-color: #333;
      min-width: 150px;
    }

    .sub-menu li a {
      padding: 10px 20px;
    }

    .nav>li:hover .sub-menu {
      display: block;
    }
  </style>
</head>

<body>
  <ul class="nav">
    <li><a href="#">菜单 1</a></li>
    <li>
      <a href="#">菜单 2</a>
      <ul class="sub-menu">
        <li><a href="#">子菜单 2.1</a></li>
        <li><a href="#">子菜单 2.2</a></li>
      </ul>
    </li>
    <li><a href="#">菜单 3</a></li>
  </ul>

  <script>
    // JavaScript 部分主要用于处理交互逻辑，此处示例中通过 CSS 实现了悬停显示子菜单的效果。
  </script>
</body>

</html>

基础概念：