滚动一屏距离

 const top_page = () => {
  if (document.documentElement.scrollTop === 0) {
            return 
        }
    let timmer;
    let h = document.documentElement.clientHeight
    let n = 0
    timmer = setInterval(() => {
        n++;
        console.log('执行')
        if (n >= h / 20) {
            clearInterval(timmer)
        }
        document.documentElement.scrollTop -= 20
    },16)
  }