JavaScript实现鼠标悬停显示下拉菜单

完整代码示例

<!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>Document</title>

    <style>
        * {
            margin: 0;
            padding: 0;
        }
        
        .nav {
            margin: 100px auto;
            width: 500px;
        }
        
        .nav>li {
            float: left;
        }
        
        li {
            list-style: none;
        }
        
        a {
            display: block;
            text-decoration: none;
            color: gray;
            height: 40px;
            width: 100px;
            text-align: center;
            line-height: 40px;
            box-sizing: border-box;
        }
        
        .nav>li>a {
            color: black;
        }
        
        .nav>li>a:hover {
            background-color: lightgray;
        }
        
        .nav>li>ul>li>a {
            /* display: none; */
            border: 1px solid orange;
            border-top: none;
        }
        
        .nav>li>ul>li>a:hover {
            background-color: lightyellow;
        }
        
        .nav>li>ul {
            display: none;
        }
    </style>
</head>

<body>
    <ul class="nav" id=nav>
        <li>
            <a href="#" >新浪</a>
            <ul>
                <li><a href="#">新闻</a> </li>
                <li><a href="#">体育</a> </li>
                <li><a href="#">快讯</a> </li>
                <li><a href="#">生活</a> </li>
                <li><a href="#">微博</a> </li>
            </ul>
        </li>
        <li>
            <a href="#" >新浪</a>
            <ul>
                <li><a href="#">新闻1</a> </li>
                <li><a href="#">体育1</a> </li>
                <li><a href="#">快讯1</a> </li>
                <li><a href="#">生活1</a> </li>
                <li><a href="#">微博1</a> </li>
            </ul>
        </li>

        <li>
            <a href="#" >新浪</a>
            <ul>
                <li><a href="#">新闻2</a> </li>
                <li><a href="#">体育2</a> </li>
                <li><a href="#">快讯2</a> </li>
                <li><a href="#">生活2</a> </li>
                <li><a href="#">微博2</a> </li>
            </ul>
        </li>


    </ul>

    <script>
        var heads = document.querySelectorAll('.nav>li');
        for (var i = 0; i < heads.length; i++) {
            heads[i].onmouseover = function() {
                this.children[1].style.display = "block";
            }
            heads[i].onmouseout = function() {
                this.children[1].style.display = "none";

            }
        }
    </script>
</body>

</html>