js实现吸顶和返回顶部

<div class="left"></div>
    <div class="container">
        <input class="search" type="text" placeholder="A-SOUL OFFICIAL">
        <input class="btn" type="button" value="搜索">
    </div>
    <div class="bTT">
        <img src="./menu/img/rr.png" alt="">
    </div>

        * {
            margin: 0;
            padding: 0;
        }


        .container {
            position: absolute;
            left: 800px;
            top: 100px;
            width: 400px;
        }

        .search {
            float: left;
            font-size: 24px;
            text-indent: 2px;
            border-radius: 5px;
        }

        .btn {
            float: left;
            width: 60px;
            font-size: 24px;
            border: none;
            background-color: slateblue;
            border-radius: 5px;
        }

        .left {
            width: 50px;
            height: 3000px;
            background-color: aqua;
        }


        .bTT {
            position: fixed;
            bottom: 100px;
            right: 100px;
            display: none;
        }

        img {
            width: 50px;
        }

    var div = document.querySelector('.container')
    var search = document.querySelector('.search')
    var btn = document.querySelector('.btn')
    var bTT = document.querySelector('.bTT')

    //window.onscroll => 浏览器滚动条滚动时触发的事件
    window.onscroll = function () {
        // 1.吸顶
        var scrollTop = document.documentElement.scrollTop
        console.log(scrollTop);
        // console.log(div);
        if (scrollTop > 100) {
            div.style.position = 'fixed'
            div.style.top = 0 + 'px'
        } else {
            div.style.position = 'absolute'
            div.style.top = 100 + 'px'
        }

        // 2.返回顶部
        if (scrollTop > 800) {
            bTT.style.display = 'block'
        } else {
            bTT.style.display = 'none'
        }

    }

    //按钮的点击事件
    bTT.onclick = function () {
        (function up() {
            setTimeout(() => {
                document.documentElement.scrollTop -= 50
                //递归出口
                if (document.documentElement.scrollTop > 0) {
                //内部调用自己 => 递归
                    up()
                }
            }, 20);
        }())
    }