原生js实现返回顶部功能

返回顶部的通用方法

function backTop(btnId) {
 var btn = document.getElementById(btnId);
 var d = document.documentElement;
 var b = document.body;
 window.onscroll = set;
 btn.style.display = "none";
 btn.onclick = function() {
   btn.style.display = "none";
   window.onscroll = null;
   this.timer = setInterval(function() {
     d.scrollTop -= Math.ceil((d.scrollTop + b.scrollTop) * 0.1);
     b.scrollTop -= Math.ceil((d.scrollTop + b.scrollTop) * 0.1);
     if (d.scrollTop + b.scrollTop == 0)
       clearInterval(btn.timer, (window.onscroll = set));
   }, 10);
 };
 function set() {
   btn.style.display = d.scrollTop + b.scrollTop > 100 ? "block" : "none";
 }
}
backTop("goTop");