https://xxianxiayubanmian.github.io/js/backtotop.js

1// back to top js
2function isHidden() {
3  let scrollTop = document.documentElement.scrollTop || document.body.scrollTop
4  if (scrollTop > 0) {
5    document.querySelector(".back-to-top").className = "back-to-top";
6  } else {
7    document.querySelector(".back-to-top").className = "back-to-top hidden";
8  }
9}
10
11const backToTop = () => {
12  let scrollTop =
13      document.documentElement.scrollTop || document.body.scrollTop,
14    delay = 10,
15    time = 200;
16  let step = Math.ceil(scrollTop * delay / time);
17  let timer = setInterval(() => {
18    scrollTop =
19      document.documentElement.scrollTop || document.body.scrollTop;
20    if (scrollTop - step <= 0) {
21      document.documentElement.scrollTop = 0;
22      document.body.scrollTop = 0;
23      clearInterval(timer);
24    } else {
25      document.documentElement.scrollTop = scrollTop - step;
26      document.body.scrollTop = scrollTop - step;
27    }
28  }, delay);
29}
30
31isHidden()
32document.addEventListener("scroll", isHidden, false);
33document.querySelector(".back-to-top").addEventListener("click", backToTop, false);