Javascript 标记群集不工作

我制作了带有标记的谷歌地图，但我有很多标记，所以我想添加标记cluterer，但它似乎不起作用。控制台上显示“未定义标记”

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创建标记，但不将其保存在任何位置。您需要创建一个标记数组，然后将其传递给MarkerCluster构造函数：

$.getJSON(urlApi, function(data) {
  const markerArray = data.map(function(item) {
    return new google.maps.Marker({
      position : {
          lat : parseFloat(item.position.lat),  
          lng : parseFloat (item.position.lng)
      });
  });
  var markerCluster = new MarkerClusterer(map, markerArray,
  {imagePath: 'https://developers.google.com/maps/documentation/javascript/examples/markerclusterer/m'});

});

    <script src="https://developers.google.com/maps/documentation/javascript/examples/markerclusterer/markerclusterer.js"></script>
    <script async defer src="https://maps.googleapis.com/maps/api/js?key=&callback=initMap"></script>
  <script src="animation-fleche.js"></script>
  <script src="slider.js"></script>
  <script src="script.js"></script>
  <script src="map.js"></script>
</body>

$.getJSON(urlApi, function(data) {
  const markerArray = data.map(function(item) {
    return new google.maps.Marker({
      position : {
          lat : parseFloat(item.position.lat),  
          lng : parseFloat (item.position.lng)
      });
  });
  var markerCluster = new MarkerClusterer(map, markerArray,
  {imagePath: 'https://developers.google.com/maps/documentation/javascript/examples/markerclusterer/m'});

});