function start() {
  window.max = 0;
  window.ntzyz = setInterval(() => {
    window.max = Math.max(document.getElementsByClassName('bilibili-player-video-danmaku')[0].childElementCount,window.max);
  }, 100);
}

function stop() {
  console.log(`最大同屏弹幕数：${window.max}`);
  clearInterval(window.ntzyz);
}

start();