scroll-to-top

scroll-to-top.js

function trackScroll() {
  let scrolled = window.pageYOffset;
  let coords = document.documentElement.clientHeight;
  if (scrolled > coords) {
    goToTop.classList.add("to_top-show");
  }
  if (scrolled < coords) {
    goToTop.classList.remove("to_top-show");
  }
}

function backToTop() {
  if (window.pageYOffset > 0) {
    window.scrollBy(0, -80);
    setTimeout(backToTop);
  }
}

let goToTop = document.querySelector(".to_top");
window.addEventListener("scroll", trackScroll);
goToTop.addEventListener("click", backToTop);

/*

<button class="to_top" type="button" aria-label="прокрутка вверх"></button>

.to_top {
  display: none;
  position: fixed;
  bottom: 30px;
  right: 10px;
  width: 40px;
  height: 40px;
  text-align: center;
  line-height: 40px;
  box-shadow: 0 0 10px 1px rgba(103, 58, 39, 0.8);
  border: none;
  background-color: transparent;
  cursor: pointer;
  border-radius: 5px;
  z-index: 999;

  &::after {
    content: '';
    position: absolute;
    top: 45%;
    left: 50%;
    transform: translate(-50%, -50%);
    border-top: none;
    border-bottom: 15px solid $basic;
    border-left: 7px solid transparent;
    border-right: 7px solid transparent;
  }
}

.to_top:active {
  box-shadow: 0 0 5px 3px rgba(103, 58, 39, 0.8);

  &::after {
    border-bottom-color: $accent;
  }
}

.to_top:focus::after {
  outline: none;
}

.to_top-show {
  display: block;
}
*/