定时器实现

借助requestAnimationFrame实现,精度更高

mySetTimeout

function mySetTimeout(callback, delay) {
  let timer; const start = Date.now()
  const loop = () => {
    if (start + delay > Date.now()) {
      timer = requestAnimationFrame(loop)
    }
    else {
      callback(timer)
    }
  }
  loop()
  return timer
}

mySetInterval

function mySetInterval(callback, delay) {
  let timer; let start = Date.now()
  const loop = () => {
    if (start + delay <= Date.now()) {
      callback(timer)
      start = Date.now()
    }
    timer = requestAnimationFrame(loop)
  }
  loop()
  return timer
}