Videoタグの再生ボタンをクリックすると、スマホの場合だけ自動的に全画面表示にする

<script>
document.addEventListener('DOMContentLoaded', function () {
  const video = document.querySelector('video');
  if (!video) return;
  video.addEventListener('play', function () {
    const isMobile = /iPhone|Android.+Mobile|iPad/.test(navigator.userAgent);
    if (isMobile && !document.fullscreenElement) {
      const requestFullScreen = video.requestFullscreen || video.webkitRequestFullscreen || video.mozRequestFullScreen || video.msRequestFullscreen;
      if (requestFullScreen) {
        requestFullScreen.call(video);
      }
    }
  });
});
</script>