// 典型的誤差累計(jì)示例
let count = 10
const timer = setInterval(() => {
  count--
  console.log(count)
}, 1000)
// 實(shí)際誤差會(huì)隨時(shí)間逐漸增大

function accurateTimer(fn, interval) {
let expected = Date.now() + interval
let timeout

const tick = () => {
    const drift = Date.now() - expected // 計(jì)算偏差
    fn()
    
    expected += interval // 更新下次預(yù)期時(shí)間
    timeout = setTimeout(tick, Math.max(0, interval - drift))
  }

  timeout = setTimeout(tick, interval)
return() => clearTimeout(timeout)
}

// main.js
const worker = new Worker('timer.worker.js')
worker.postMessage({ cmd: 'start', interval: 1000 })

// timer.worker.js
self.addEventListener('message', (e) => {
  setInterval(() => {
    self.postMessage('tick')
  }, e.data.interval)
})

async function syncTime() {
  const start = Date.now()
  const res = await fetch('/api/time')
  const serverTime = await res.json()
  const latency = Date.now() - start
  
  return serverTime + Math.floor(latency/2) // 假設(shè)網(wǎng)絡(luò)延遲對(duì)稱
}

const start = performance.now()

function check() {
  const elapsed = performance.now() - start
  if(elapsed >= 1000) {
    // do something
    start = performance.now() 
  }
  requestAnimationFrame(check)
}

document.addEventListener('visibilitychange', () => {
  if(document.hidden) {
    clearInterval(timer)
    // 記錄剩余時(shí)間
  } else {
    // 重新校準(zhǔn)后啟動(dòng)
  }
})