* {
            margin: 0;
            padding: 0;
        }
        
        .box {
            width: 400px;
            height: 300px;
            border: 1px solid #000;
            margin: 100px auto;
        }
        
        .top {
            list-style: none;
            width: 100%;
            height: 50px;
            line-height: 50px;
            text-align: center;
            display: flex;
            justify-content: space-between;
        }
        
        .top>li {
            width: 80px;
            height: 100%;
            background: skyblue;
            border-right: 1px solid #ccc;
        }
        
        .top>li:last-child {
            border-right: none;
        }
        
        .bottom {
            width: 100%;
            height: 250px;
        }
        
        .bottom>.content {
            width: 100%;
            height: 100%;
            display: none;
        }
        
        .bottom>.content:nth-child(1) {
            background: red;
            display: block;
        }
        
        .bottom>.content:nth-child(2) {
            background: blue;
        }
        
        .bottom>.content:nth-child(3) {
            background: green;
        }
        
        .bottom>.content:nth-child(4) {
            background: yellow;
        }
        
        .bottom>.content:nth-child(5) {
            background: purple;
        }
        
        .current {
            background: red !important;
        }

    <div class="box">
        <ul class="top">
            <li class="current">新闻</li>
            <li>视频</li>
            <li>音乐</li>
            <li>军事</li>
            <li>财经</li>
        </ul>
        <div class="bottom">
            <div class="content">新闻的内容</div>
            <div class="content">视频的内容</div>
            <div class="content">音乐的内容</div>
            <div class="content">军事的内容</div>
            <div class="content">财经的内容</div>
        </div>
    </div>
    <script>
        // 1.拿到需要操作的元素
        let oItems = document.querySelectorAll("li");
        let oDivs = document.querySelectorAll(".content");

        // 定义变量保存上一次设置的索引
        let previousIndex = 0;

        // 2.给所有的选项卡添加点击事件
        for (let i = 0; i < oItems.length; i++) {
            let item = oItems[i];
            // item.setAttribute("index", i);

            item.onmousemove = function() {
                // 清空上一次对应的元素对应的样式
                let preItem = oItems[previousIndex];
                preItem.className = "";
                let preDiv = oDivs[previousIndex];
                preDiv.style.display = "none";

                // 设置当前这一次的元素对应的样式
                // let index = this.getAttribute("index");
                this.className = "current";
                let oDiv = oDivs[i];
                oDiv.style.display = "block";

                // 保存当前这一次的索引
                previousIndex = i;
            };
        }
    </script>