javascript implements back to top effects

HTML:

<input id="btn1" type="button" value=" Back to the top " />

CSS:

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

JS:

window.onload=funcition(){
  var oBtn=document.getElementById("btn");
  var timer=null;
  // statement 1 Three variables to see whether the system or the user scrolls 
  var sBys=true;
  window.onscroll=funcition(){
    if(!sBys){
      clearInterval(timer);
    }
    sBys=false;
  }
  oBtn.onclick=funcition(){
    timer = setInterval(funcition(){
      // To obtain scrollTop
      var scrollTop=document.documentElement.scrollTop||document.body.scrollTop;
      // Calculate the buffering speed when the button is clicked back to the top 
      var ispeed=Math.floor(-scrollTop/8);
      if(scrollTop==0){
        clearInterval(timer)
      }
      sBys=true;
      document.documentElement.scrollTop=document.body.scrollTop=scrollTop+ispeed;
    },30)
  }
}

Knowledge:

1. Calculate speed (buffer) and round down
2. Clear the timer when scrollTop==0
3. Need to determine whether it is user or js operation scroll bar, if it is user operation, clear the timer

This is the end of this article, I hope you enjoy it.