js滚动条如何缓慢的回到顶部？

function top() {
            let currentPosition, timer
          timer = setInterval(function () {
            currentPosition = document.documentElement.scrollTop || document.body.scrollTop
            currentPosition -= 10
            if (currentPosition > 0) {
              window.scrollTo(0, currentPosition)
            } else {
              window.scrollTo(0, 0)
              clearInterval(timer)
            }
          }, 1) 
}

top()