页面横向滚动 联动 进度条

//效果图

*{margin: 0;padding: 0;}
.wrap{
100%;height: 100%;display: flex;
flex: 1;flex-direction: column;
}
.boy1{
100%;overflow: auto;
}
.myFan{
400%;height: 150px;display: flex;
}
.myFan>div{
25%;height: 150px;border-right: 1px solid blueviolet;
text-align: center;line-height: 150px;
}
.boy2{
100%;display: flex;
justify-content: center;
}
.boy2>div{
100px;background: grey;
border-radius: 5px;
}
.myScrollBar{
padding: 0.3rem 0;background: red;
border-radius: 5px;
}

   <div class="wrap">
        <div class="boy1">
            <div class="myFan">
                <div>1</div>
                <div>2</div>
                <div>3</div>
                <div>4</div>
            </div>
        </div>
        <div class="boy2">
            <div>
                <p class="myScrollBar"></p>
            </div>
        </div>
    </div>

js

var boy1 = document.getElementsByClassName("boy1")[0],  //获取元素
myScrollBar = document.getElementsByClassName("myScrollBar")[0],
myFan = document.getElementsByClassName("myFan")[0];

myScrollBar.style.width = "25px";

boy1.onscroll= function(){
　　let nu = boy1.scrollLeft/boy1.offsetWidth/4; //移动的距离 / 获取显示的盒子宽  获取到一个百分比
　　myScrollBar.style.marginLeft = 100*nu+"px";  //获取到的百分比处理下直接赋值回去
}