38.setInterval方法

function mySetInterval(callback, interval) {
  var timer = null;
  var now = Date.now;
  var startTime = now();
  var endTime = startTime;
  var loop = function() {
    timer = requestAnimationFrame(loop); // 使用requestAnimationFrame
    endTime = now();
    if(endTime - startTime >=interval) {
      startTime = endTime = now();
      callback && callback(timer);
    }
  }
  timer = requestAnimationFrame(loop);
  return timer;
}
var count = 0;
mySetInterval(function(timer){
  console.log('超级定时器已部署');
  count++;
  if(count>=3) {
    cancelAnimationFrame(timer);
  }
}, 500)