Hook实现倒计时

import React, {useEffect, useState} from 'react';
import { connect } from 'dva';
import styles from './IndexPage.css';

let timer;
function IndexPage() {
  const [count, setCount] = useState(0)
  useEffect(()=>{
    clearInterval(timer)
    return ()=>{
      clearInterval(timer)
    }
  },[])
  useEffect(()=>{
    if ( count === 5){
      timer = setInterval(()=> setCount( t => --t),1000)
    } else if( count === 0){
      clearInterval(timer)
    }
  },[count])
  const handclick = () => {
    setCount(5)
  };
  return (
    <div className={styles.normal}>
        <div className={styles.buttons} onClick={handclick}>
          {count}获取
          </div>
    </div>
  );
}

export default connect()(IndexPage);