Vanilla Javascript scrolling

scrollToTop.js

scrollToTop = (scrollDuration) => {
      if(navigator.userAgent.match(/Trident\/7\./)) { // if IE
        window.scrollTo(0, 0);
      } else {
        const scrollHeight = window.scrollY,
          scrollStep = Math.PI / (scrollDuration / 15),
          cosParameter = scrollHeight / 2;
        var scrollCount = 0,
          scrollMargin,
          scrollInterval = setInterval(function() {
            if (window.scrollY !== 0) {
              scrollCount = scrollCount + 1;
              scrollMargin = cosParameter - cosParameter * Math.cos(scrollCount * scrollStep);
              window.scrollTo(0, (scrollHeight - scrollMargin));
            }
            else clearInterval(scrollInterval);
          }, 15);
      }
    }