React 监听页面滚动

const scrollEvent = event => {
 if (!event.srcElement.scrollTop) {
    //处理向上使劲滚动的时候scrollTop为undefined
    return undefined
  }
  // 滚动的高度
  const scrollTop =
    (event.srcElement ? event.srcElement.scrollTop : false) ||
    window.pageYOffset ||
    (event.srcElement ? event.srcElement.body.scrollTop : 0)
  // 视窗高度
  const clientHeight = (event.srcElement && event.srcElement.clientHeight) || document.body.clientHeight
  // 页面高度
  const scrollHeight = (event.srcElement && event.srcElement.scrollHeight) || document.body.scrollHeight
  // 距离页面底部的高度
  const height = scrollHeight - scrollTop - clientHeight

  return height
}

const initialState = {
  page: 1,
  pageSize: 50
}

const reducer = (state, action) => {
  const payload = reap(action, 'payload', {})
  switch (action.type) {
    case 'update':
      return { ...state, ...payload }
    default:
      throw new Error()
  }
}

function Demo(props) {
  const {
    getList
  } = props

  const [hasMore, setHasMore] = useState(true)
  const [state, dispatch] = useReducer(reducer, initialState)
  const [list, setList] = useState([])

  const _handleScroll = useCallback(
    event => {
      const height = scrollEvent(event)

      if (hasMore && height <= 100) {
        const page = state.page + 1
        //get new list data
        dispatch({
          type: 'update',
          payload: {
            page
          }
        })
      }
    },
    [hasMore, state.page]
  )

  useEffect(() => {
    const scrollDom = document.getElementById('layoutContentContainer')
    scrollDom.addEventListener('scroll', _handleScroll)

    return () => scrollDom.removeEventListener('scroll', _handleScroll)
  }, [_handleScroll])

  useEffect(() => {
    const { page, pageSize, searchText } = state
    getList({ page, pageSize, name: searchText }).then(res => {
      const code = reap(res, 'code', 0)
      if (code === 200) {
            //判断设置还有没有数据可以加载了  setHasMore()
           //设置获取的数据列表setList(a => a.concat(list))
      }
    })
  }, [getList, state])

  return (
    
        {/** show list map to ui */}
    
  )
}
Demo.propTypes = {
  getList: PropTypes.func
}

export default Demo

scrollEvent函数在是计算滚动条距离距离底部的高。
挂载scroll事件监听触发计算当滚动条距离底部小于等于100时进行再次数据加载