JavaScript实现下拉菜单的显示与隐藏

<!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>操作元素-新浪下拉菜单</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        
        ul li {
            list-style: none;
        }
        
        a {
            text-decoration: none;
            color: #4c4c4c;
        }
        
        a:hover {
            color: #e88415;
        }
        
        .box {
            width: 80px;
            margin: 50px auto;
            font-size: 14px;
            color: #4c4c4c;
        }
        
        .weibo {
            position: relative;
            background-color: #fcfcfc;
        }
        
        .weibo a {
            display: block;
            height: 40px;
            line-height: 40px;
            padding-left: 20px;
        }
        
        .change {
            color: #f9a74f;
            background-color: #edeef0;
        }
        
        i {
            position: absolute;
            top: 50%;
            right: 15px;
            margin-top: -4px;
            width: 5px;
            height: 5px;
            border-bottom: 1px solid orangered;
            border-right: 1px solid orangered;
            transform: rotate(45deg);
        }
        
        .weiboList {
            display: none;
        }
        
        .weiboList li a {
            display: block;
            width: 80px;
            height: 33px;
            line-height: 33px;
            padding-left: 15px;
            border-bottom: 1px solid #fecc5b;
            background-color: #fff;
        }
        
        .weiboList li a:hover {
            background-color: #fff5da;
        }
    </style>
</head>

<body>
    <div class="box">
        <div class="weibo"><a href="#" >微博<i class="select"></i></a></div>
        <ul class="weiboList">
            <li><a href="#" >私信</a></li>
            <li><a href="#" >评论</a></li>
            <li><a href="#" >@我</a></li>
        </ul>
    </div>

    <script>
        var box = document.querySelector('.box');
        var weibo = document.querySelector('.weibo');
        var weiboList = document.querySelector('.weiboList');

        box.onmouseover = function() {
            weibo.className = 'weibo change'
            weiboList.style.display = 'block';

        }

        box.onmouseout = function() {
            weibo.className = 'weibo';
            weiboList.style.display = 'none';
        }
    </script>
</body>

</html>