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;