11 异步：事件循环

const eventloop = {
  queue: [],

  loop() {
    while (this.queue.length) {
      var callback = this.queue.shift();
      callback();
    }

    setTimeout(this.loop.bind(this), 50);
  },

  add(callback) {
    this.queue.push(callback);
  },
};

eventloop.loop();

setTimeout(() => eventloop.add(() => console.log("1")), 500);
setTimeout(() => eventloop.add(() => console.log("2")), 800);