JS implements return to top special effects

<input id="btn1" type="button" value="回到顶部" />

#btn1{position:fixed;bottom:10px;right:10px;}

window.onload=funcition(){
    var oBtn=document.getElementById("btn");
    var timer=null;
    //申明一个变量看是否为系统还是用户滚动
    var sBys=true;
    window.onscroll=funcition(){
        if(!sBys){
            clearInterval(timer);
        }
        sBys=false;
    }
    oBtn.onclick=funcition(){
       timer = setInterval(funcition(){
            //获取scrollTop
            var scrollTop=document.documentElement.scrollTop||document.body.scrollTop;
            //当点击按钮回到顶部时计算缓冲速度
            var ispeed=Math.floor(-scrollTop/8);
            if(scrollTop==0){
                clearInterval(timer)
            }
            sBys=true;
            document.documentElement.scrollTop=document.body.scrollTop=scrollTop+ispeed;
        },30)
    }
}

Knowledge points: 1. The calculation speed (buffering) is rounded down

2. When scrollTop==0, the timer needs to be cleared

3. It is necessary to determine whether the user or js operates the scroll bar. If it is a user operation, Clear timer