js如何做倒计时

// 设置倒计时的结束时间，例如从现在起10分钟后
let endTime = new Date(new Date().getTime() + 10 * 60 * 1000);

function updateCountdown() {
    let now = new Date().getTime();
    let distance = endTime - now;

    if (distance < 0) {
        clearInterval(interval);
        document.getElementById("countdown").innerHTML = "倒计时结束";
        return;
    }

    let minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
    let seconds = Math.floor((distance % (1000 * 60)) / 1000);

    document.getElementById("countdown").innerHTML = minutes + "分 " + seconds + "秒 ";
}

// 每秒更新倒计时
let interval = setInterval(updateCountdown, 1000);

// 检查是否有存储的结束时间
if (localStorage.getItem("endTime")) {
    endTime = new Date(localStorage.getItem("endTime"));
} else {
    endTime = new Date(new Date().getTime() + 10 * 60 * 1000);
    localStorage.setItem("endTime", endTime);
}

// 在updateCountdown函数中更新localStorage中的结束时间
function updateCountdown() {
    // ...原有代码...
    localStorage.setItem("endTime", endTime);
}