Плавное появление и исчезновение блока при прокрутке на чистом javascript

Question

window.addEventListener('DOMContentLoaded', function() {
    const scrollUpButton = document.querySelector('.backToTop');

    if (scrollUpButton) {
        scrollUpButton.addEventListener('click', function name() {
            window.scrollTo({
                top: 0,
                behavior: 'smooth',
            });
        });

        window.addEventListener('scroll', function() {
            const scrolled = window.pageYOffset || document.documentElement.scrollTop;

            if (scrolled >= 800) {
                scrollUpButton.classList.add('backToTop_visible');
            } else {
                scrollUpButton.classList.remove('backToTop_visible');
            }
        });
    }
});

.backToTop {
  display: none;
  position: fixed;
  width: 45px;
  height: 45px;
  background-color: #000;
  line-height: 45px;
  text-align: center;
  color: #fff;
  top: auto;
  left: auto;
  right: 60px;
  bottom: 120px;
  cursor: pointer;
  border-radius: 2px;
  transition: opacity .3s ease-in;
  opacity: 0.6;
}

.backToTop::before {
  display: inline-block;
  position: relative;
  vertical-align: middle;
  content: '';
  background-image: url("../img/sprites/svgSprites.svg#backToTop");
  background-repeat: no-repeat;
  background-size: 20px 20px;
  width: 20px;
  height: 20px;
}

.backToTop:hover {
  opacity: 1;
}

.backToTop_visible {
  display: block;
}

<div class="backToTop page__backToTop icon_backToTop"></div>

Answer 1

Может быть так ?

Смотреть на весь экран

let body = document.querySelector("body");
let bHeight = body.getBoundingClientRect().height;
let screenY = window.innerHeight / 2;
let btn = document.querySelector("#btn");

window.onscroll = function() {
  if (pageYOffset > screenY) {
    btn.classList.add("fixed");
  } else {
    btn.classList.remove("fixed");
  }
}

btn.onclick = function() {
  window.scrollTo({
    top: 0,
    behavior: 'smooth',
  });
}

body {
  margin: 0;
}

section {
  height: 100vh;
}

section:nth-child(1) {
  background: red;
}

section:nth-child(2) {
  background: green;
}

section:nth-child(3) {
  background: blue;
}

section:nth-child(4) {
  background: pink;
}

section:nth-child(5) {
  background: yellow;
}

#btn {
  position: fixed;
  bottom: 30px;
  right: 30px;
  transform: scale(0);
  transition: 0.34s linear;
}

#btn.fixed {
  transform: scale(1);
}

<section></section>
<section></section>
<section></section>
<section></section>
<section></section>

<button id="btn">Вверх</button>

БЛОГ НА HUSL

Плавное появление и исчезновение блока при прокрутке на чистом javascript

Ответы (1 шт):