react实现简单倒计时

今天遇到一个简单的小功能，看网上的一些方法感觉不太适合，所以就手敲了一个，直接上代码！！！

 import React, { Component } from 'react';

 class NoTimeContent extends Component {
     constructor(props) {
         super(props)
         this.state = {
             day: 0,
             hour: 0,
             minute: 0,
             second: 0
         }
     }
     render() {
         return (
             <NoTimeCon>
                 <h2>
                     <span>限时秒杀</span>
                     <span>{this.state.day}天 {this.state.hour}:{this.state.minute}:{this.state.second}</span>
                 </h2>
             </NoTimeCon>
         )
     }

 componentDidMount() {
       const end = Date.parse(new Date('2018-11-29 24:00'))
       this.countFun(end);
     }

   //卸载组件取消倒计时
   componentWillUnmount(){
     clearInterval(this.timer);
   }

   countFun = (end) => {

     let now_time = Date.parse(new Date());
     var remaining = end - now_time;

     this.timer = setInterval(() => {
         //防止出现负数
       if (remaining > 1000) {
         remaining -= 1000;
         let day = Math.floor((remaining / 1000 / 3600) / 24);
         let hour = Math.floor((remaining / 1000 / 3600) % 24);
         let minute = Math.floor((remaining / 1000 / 60) % 60);
         let second = Math.floor(remaining / 1000 % 60);

         this.setState({
             day:day,
             hour:hour < 10 ? "0" + hour : hour,
             minute:minute < 10 ? "0" + minute : minute,
             second:second < 10 ? "0" + second : second
         })
       } else {
         clearInterval(this.timer);
         //倒计时结束时触发父组件的方法
         //this.props.timeEnd();
       }
     }, 1000);
   }

 }
 export default NoTimeContent;