实现倒计时

  countdown() {
    let that = this;
    // 目标日期时间戳
    const end = new Date('2021-4-30')
    // 当前时间戳
    const now = new Date()
    // 相差的毫秒数
    const msec = end - now
    // 计算时分秒数
    let day = parseInt(msec / 1000 / 60 / 60 / 24)
    let hr = parseInt(msec / 1000 / 60 / 60 % 24)
    let min = parseInt(msec / 1000 / 60 % 60)
    let sec = parseInt(msec / 1000 % 60)
    // 个位数前补零
    hr = hr > 9 ? hr : '0' + hr
    min = min > 9 ? min : '0' + min
    sec = sec > 9 ? sec : '0' + sec
    // 控制台打印
    console.log(`${day}天 ${hr}小时 ${min}分钟 ${sec}秒`)
    // 一秒后递归
    setTimeout(function () {
      that.countdown()
    }, 1000)
  },