Smooth Scroll to the Top of the Page With JavaScript

Get distance from top using Document.documentElement or Document.body and Element.scrollTop.

Scroll by a fraction of the distance from the top.

Use Window.requestAnimationFrame() to animate the scrolling.

const scrollToTop = () => {
  const c = document.documentElement.scrollTop || document.body.scrollTop;
  if (c > 0) {
    window.requestAnimationFrame(scrollToTop);
    window.scrollTo(0, c - c / 8);
  }
};

Source

https://www.30secondsofcode.org/js/s/scroll-to-top