js轮播页面,点击切换

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        html,
        body {
            width: 100%;
            height: 100%;
        }

        #container {
            position: absolute;
            z-index: -2;
            width: 100%;
        }

        .box {
            width: 100%;
            height: 768px;
            font-size: 100px;
            text-align: center;
            line-height: 768px;
        }

        .box:nth-of-type(even) {
            background-color: red;
        }

        .box:nth-of-type(odd) {
            background-color: blue;
        }

        #btn {
            width: 50px;
            height: 250px;
            position: fixed;
            top: 250px;
            left: 50px;
        }

        #btn>button {
            width: 50px;
            height: 50px;
            display: block;
        }
    </style>
</head>

<body>
    <div id="btn">
        <button>1</button>
        <button>2</button>
        <button>3</button>
        <button>4</button>
    </div>
    <section id="container">
        <div class="box">1</div>
        <div class="box">2</div>
        <div class="box">3</div>
        <div class="box">4</div>
    </section>

    <script>
        var btn = document.getElementsByTagName("button");
        var box = document.getElementsByClassName("box");
        var container = document.getElementById("container")
        btn[0].style.backgroundColor = "red"
        window.onscroll = function () {
            var positionTop = document.documentElement.scrollTop;
            console.log(positionTop)
            //偏移量除以768，向下取整
            for (var i = 0, len = btn.length; i < len; i++) {
                btn[i].style.backgroundColor = ""
            }
            var index = Math.floor(positionTop / 768);
            btn[index].style.backgroundColor = 'red'
        }
        //点击切换页面
        var arr = [];
        for (var j = 0, len = btn.length; j < len; j++) {
            arr.push(btn[j]);
            arr[j].onclick = function () {
                // console.log(arr.indexOf(this))
                var index = arr.indexOf(this);
                // console.log(index)
                for (var i = 0, len = btn.length; i < len; i++) {
                    btn[i].style.backgroundColor = ""
                }
                this.style.backgroundColor = "red"
                // container.style.top = -(index * 768) + "px";
                document.documentElement.scrollTop = index * 768;
                // console.log( index * 768 + "px")
                // console.log(document.documentElement.scrollTop)
                // console.log(index * 768)
            }
        }
    </script>
</body>

</html>
js轮播页面,点击切换

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