js秒为单位做倒计时

例子：倒计时分钟

//倒计时
let timeValue = ref('10:00')
let countdownInterval = ref(null)
const getCountDown = () => {
  countdown.value = 600;//600秒10分钟
  let hours=0
  let minutes=0
  let seconds =0
  // 倒计时效果
  if (countdownInterval.value) clearInterval(countdownInterval.value)//重点、定时器清不掉
  countdownInterval.value = setInterval(() => {
    countdown.value--;
    let minutes = Math.floor((countdown.value / 60));
    let seconds = Math.floor(countdown.value % 60)
   if (countdown.value <= 0) {
      clearInterval(countdownInterval.value);
    }
  }, 1000);
}

超过一小时的倒计时：

//倒计时
let timeValue = ref('10:00')
let countdownInterval = ref(null)
const getCountDown = () => {
  countdown.value = 600;
  let hours=0
  let minutes=0
  let seconds =0
  // 倒计时效果
   if (countdownInterval.value) clearInterval(countdownInterval.value)//重点、定时器清不掉
  countdownInterval.value = setInterval(() => {
    countdown.value--;
    let minutes = Math.floor((countdown.value / 60));
    let seconds = Math.floor(countdown.value % 60)
    if(minutes > 60) {
	    //获取小时，获取分钟除以60，得到整数小时
	     hourTime = parseInt(minutes / 60);
	     //获取小时后取佘的分，获取分钟除以60取佘的分
	     minuteTime = parseInt(minutes % 60);
	}
   if (countdown.value <= 0) {
      clearInterval(countdownInterval.value);
    }
  }, 1000);
}