将视频观看行为发送给GA。数据未发送

Question

我想将数据发送到Google Analytics（分析），以衡量用户观看多个视频的行为-我想知道他们是否玩过Cideo，观看了25％，50％，75％或100％。以下代码未将数据发送到GA。我不确定我的问题是否属于Google Analytics（分析）或javascript或两者兼而有之。请帮忙。谢谢。

<video id="v1" src="/v1.mp4" width="400px" height="200px" controls />
<video id="v2" src="/v2.mp4" width="400px" height="200px" controls />


<script type="text/javascript">
(function() {
  document.addEventListener('DOMContentLoaded', init, false);
  var videoId, dur, quarter, stat;

  function init() {
    for (var video of document.querySelectorAll('video')) {
      video.addEventListener('play', videoPlay, false);
      video.addEventListener('ended', videoEnd, false);
      video.addEventListener('timeupdate', videoTimeUpdate, false);
    }
  }

  function setKeyFrames(duration) {
    if (dur) {
      return;
    }
    dur = duration;
    quarter = duration / 4;
  }

  function videoTimeUpdate(e) {
    var videoId = e.target;
    var curTime = videoId.currentTime;
    if (curTime >= quarter && curTime < quarter * 2 && stat !== 1) {
      gtag('event', 'Watched Video', {
        'event_category': 'Video',
        'event_label': 'Watched 25% of ' + videoId.id
      });
      stat = 1;

    } else if (curTime >= quarter * 2 && curTime < quarter * 3 && stat !== 2) {
      gtag('event', 'Watched Video', {
        'event_category': 'Video',
        'event_label': 'Watched 50% of ' + videoId.id
      });
      stat = 2;

    } else if (curTime >= quarter * 3 && curTime < dur && stat !== 3) {
      gtag('event', 'Watched Video', {
        'event_category': 'Video',
        'event_label': 'Watched 75% of ' + videoId.id
      });
      stat = 3;

    }
  }

  function videoPlay(e) {
    var videoId = e.target;
    gtag('event', 'Watched Video', {
      'event_category': 'Video',
      'event_label': 'Video Played Is ' + videoId.id
    })
    setKeyFrames(this.duration);

  }


  function videoEnd(e) {
    var videoId = e.target;
    stat = 4;
    gtag('event', 'Watched Video', {
        'event_category': 'Video',
        'event_label': 'Watched ALL of ' + videoId.id
      });

  }



})();


</script>