JS 筋斗云案例

        .nav {
            width: 1000px;
            height: 60px;
            line-height: 60px;
            margin: 0 auto;
            position: relative;
        }

        ul {
            width: 100%;
            height: 100%;
            padding: 0;
            list-style: none;
        }

        ul li {
            float: left;
            width: 100px;
            line-height: 60px;
            text-align: center;
        }

        .cloud {
            display: inline-block;
            position: absolute;
            width: 50px;
            height: 30px;
            background-color: pink;
            left: 0;
        }

        ul li>a {
            color: black;
            text-decoration: none;
        }

<div class="nav">
        <span class="cloud"></span>
        <ul>
            <li class="current">首页</li>
            <li><a href="#">团队力量</a></li>
            <li><a href="#">企业文化</a></li>
            <li><a href="#">成功案例</a></li>
            <li><a href="#">招聘信息</a></li>
            <li><a href="#">公司简介</a></li>
            <li><a href="#">成功案例</a></li>
            <li><a href="#">招聘信息</a></li>
            <li><a href="#">公司简介</a></li>
        </ul>
    </div>

 var cloud = document.querySelector('.cloud')
        var nav = document.querySelector('.nav')
        var lis = nav.querySelectorAll('li')
        // console.log(cloud);
        var current = 0;

        for (var i = 0; i < lis.length; i++) {
            lis[i].addEventListener('mouseenter', function () {
                animate(cloud, this.offsetLeft)
            })
            // 鼠标离开
            lis[i].addEventListener('mouseleave', function () {
                animate(cloud, current)
            })
            // 鼠标点击
            lis[i].addEventListener('click', function () {
                current = this.offsetLeft;
            })
        }

        function animate(obj, target, callback) {
            clearInterval(obj.timer)
            obj.timer = setInterval(function () {
                // 把移动值改为整数避免存在小数
                var step = (target - obj.offsetLeft) / 10;
                step = step > 0 ? Math.ceil(step) : Math.floor(step);
                if (obj.offsetLeft == target) {
                    clearInterval(obj.timer)
                    // 回调函数写在定时器结束后面
                    callback && callback();
                }
                // 把里面的移动值改为慢慢变小的值
                obj.style.left = obj.offsetLeft + step + 'px'
            }, 15)
        }