基于JS解决前端实现倒计时有误差的方法(面试官常问)

let serverTime = null;
let timeDiff = 0;
// 获取服务器时间
fetch('/api/server-time')
  .then(response => response.json())
  .then(data => {
    serverTime = new Date(data.time);
    timeDiff = serverTime.getTime() - Date.now();
    startCountdown();
  });
// 定期校准
setInterval(() => {
  fetch('/api/server-time')
    .then(response => response.json())
    .then(data => {
      serverTime = new Date(data.time);
      timeDiff = serverTime.getTime() - Date.now();
    });
}, 60000); // 每分钟校准一次
// 开始倒计时
function startCountdown() {
  const countdownTime = serverTime.getTime() + timeDiff + 10 * 60 * 1000; // 假设倒计时为10分钟
  const timer = setInterval(() => {
    const now = Date.now() + timeDiff;
    const remainingTime = countdownTime - now;
    if (remainingTime > 0) {
      const minutes = Math.floor(remainingTime / 60000);
      const seconds = Math.floor((remainingTime % 60000) / 1000);
      console.log(`${minutes}分${seconds}秒`);
    } else {
      console.log('倒计时结束');
      clearInterval(timer);
    }
  }, 1000);
}

// 主线程
const worker = new Worker('countdown.worker.js');
worker.onmessage = function(e) {
  console.log('倒计时剩余时间：' + e.data);
};
worker.postMessage(10); // 10秒倒计时
// countdown.worker.js (Web Worker文件)
self.onmessage = function(e) {
  let count = e.data;
  const timer = setInterval(function() {
    count--;
    self.postMessage(count);
    if (count === 0) {
      clearInterval(timer);
    }
  }, 1000);
};

let firstStamp = null; // 倒计时开始的时间戳
let lastStamp = null;  // 上一次更新的时间戳
let timer = null;      // 定时器
let total = 10;        // 倒计时总时间（10秒）
// 监听页面可见性变化
document.addEventListener('visibilitychange', handleVisibilityChange);
// 页面可见性变化处理函数
function handleVisibilityChange() {
    // 当页面变为可见状态时，修正倒计时
    if (document.visibilityState === 'visible') {
        updateCount();
    }
}
// 开始倒计时
function startCountdown() {
    firstStamp = Date.now(); // 记录倒计时开始的时间戳
    lastStamp = firstStamp;
    updateCount(); // 初始化倒计时显示
}
// 更新倒计时
function updateCount() {
    clearTimeout(timer); // 清除旧的定时器
    const nowStamp = Date.now(); // 当前时间戳
    const pastTime = nowStamp - firstStamp; // 已经过的时间
    const remainTime = total * 1000 - pastTime; // 剩余时间
    if (remainTime > 0) {
        // 更新倒计时显示
        const seconds = Math.floor(remainTime / 1000);
        console.log(`剩余时间：${seconds}秒`);
        lastStamp = nowStamp; // 更新上一次更新的时间戳
        // 设置新的定时器，确保下次定时器在剩余时间的基础上执行
        timer = setTimeout(updateCount, remainTime % 1000);
    } else {
        console.log('倒计时结束');
    }
}
// 启动倒计时
startCountdown();

function accurateTimer(fn, interval) {
  let expected = Date.now() + interval;
  let timeout;
  const tick = () => {
    const drift = Date.now() - expected; // 计算偏差
    fn();
    expected += interval; // 更新下次预期时间
    timeout = setTimeout(tick, Math.max(0, interval - drift));
  };
  timeout = setTimeout(tick, interval);
  return () => clearTimeout(timeout);
}
// 使用示例
let count = 10;
const stopTimer = accurateTimer(() => {
  count--;
  console.log(count);
  if (count === 0) {
    stopTimer();
  }
}, 1000);

let startTime = performance.now();
const totalDuration = 10000; // 10秒倒计时
const countDown = () => {
  const elapsedTime = performance.now() - startTime;
  const remainingTime = totalDuration - elapsedTime;
  if (remainingTime > 0) {
    console.log(Math.floor(remainingTime / 1000));
    requestAnimationFrame(countDown);
  } else {
    console.log('倒计时结束');
  }
};
requestAnimationFrame(countDown);