react 获取服务器端时间倒计时

import React, { Component } from 'react'
import axios from 'axios'

export default class Timer extends Component {

  constructor(props) {
    super(props)
    this.state = {
      bool: false,
      days: '0',
      hours: '00',
      minutes: '00',
      seconds: '00'
    }
  }

  componentDidMount() {
    this.start()
  }

  async start() {
    this.timer && clearTimeout(this.timer) // 先清除一遍定时器，避免被调用多次
    // 发起任意一个服务器请求， 然后从headers 里获取服务器时间
    let leftTime = await axios.get('/').then(response => {
      return new Date(this.props.date).getTime() - new Date(response.headers.date).getTime() // 服务器与倒计时的 时间差
    }).catch(error => {
      console.log(error)
      return 0 // 这里发送的服务器请求失败 设为0
    })

    // 倒计时
    this.timer = setInterval(() => {
      leftTime = leftTime - 1000
      let { bool, days = '0', hours = '00', minutes = '00', seconds = '00' } = this.countdown(leftTime)
      if (bool) { // 结束倒计时
        clearTimeout(this.timer)
      }
      this.setState({
        bool,
        days,
        hours,
        minutes,
        seconds
      })
    }, 1000)
  }

  /**
   * 倒计时
   * @param leftTime 要倒计时的时间戳
   */
  countdown(leftTime) {
    let bool = false
    if (leftTime <= 0) {
      bool = true
      return { bool }
    }
    var days = parseInt(leftTime / 1000 / 60 / 60 / 24, 10) //计算剩余的天数
    var hours = parseInt(leftTime / 1000 / 60 / 60 % 24, 10)
    if (hours < 10) {
      hours = '0' + hours
    }
    var minutes = parseInt(leftTime / 1000 / 60 % 60, 10)
    if (minutes < 10) {
      minutes = '0' + minutes
    }
    var seconds = parseInt(leftTime / 1000 % 60, 10)
    if (seconds < 10) {
      seconds = '0' + seconds
    }
    return { bool, days, hours, minutes, seconds }
  }

  componentWillUnmount() {
    clearTimeout(this.timer)
  }

  render() {
    let { bool, days, hours, minutes, seconds } = this.state
    return (
      <div>
        {
          bool ?
            <div>活动已结束</div> :
            <div>
              {days} 天 {hours} : {minutes} : {seconds}
            </div>
        }
      </div>
    )
  }
}