js返回页面顶部特效代码

使用方法

let toTopBtn = document.getElementById('back-top__content--desk');

toTopBtn.addEventListener('click', function (e) {
  e.preventDefault();
  window.scrollTo({ top: 0, behavior: "smooth" });
});

let scrollPos = 0;

window.addEventListener('scroll', function () {

  if (document.body.getBoundingClientRect().top > scrollPos) {
    console.log('scrolling down');

    document.getElementById('back-top').classList.remove('active');

  } else {
    document.getElementById('back-top').classList.add('active');
    console.log('scrolling up');
  }

  scrollPos = document.body.getBoundingClientRect().top;
});