Marker Clusterer in Google Maps

HTML

<div id="map"></div>
 <!-- Replace the value of the key parameter with your own API key. -->
<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=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk&callback=initMap">
</script>

CSS

#map {
  height: 100%;
}

html, body {
  height: 100%;
  margin: 0;
  padding: 0;
}

JavaScript

var MrkId = 62440;
var markersC = [];
var markersA = [];
var infowindow;
var map;
var markerCluster;

var points = [
  ['Point 1', 'adresse 1 ', 46.613317, 2.249830, 62437],
  ['Point 2', 'adresse 2 ', 46.713317, 2.249830, 62438],
  ['Point 3', 'adresse 3 ', 46.613317, 2.349830, 62439],
  ['Point 4', 'adresse 4 ', 46.713317, 2.449830, 62440],
  ['Point 5', 'adresse 5 ', 46.613317, 2.449830, 62441],
  ['Point 1', 'adresse 1 ', 46.413317, 2.249830, 62442],
  ['Point 2', 'adresse 2 ', 46.513317, 2.249830, 62443],
  ['Point 3', 'adresse 3 ', 46.513317, 2.349830, 62444],
  ['Point 4', 'adresse 4 ', 46.413317, 2.449830, 62445],
  ['Point 5', 'adresse 5 ', 46.513317, 2.449830, 62446],
];

function initMap() {
  map = new google.maps.Map(document.getElementById('map'), {
    center: {
      lat: 46.613317,
      lng: 2.349830
    },
    zoom: 9
  });

  infowindow = new google.maps.InfoWindow();
  setMarkers();
}

function MkrClick(Mrk, Cnt, point) {
  var contentString = '<div class="marker-infowindow">' + '<h2>' + point[0] + '</h1>' + '<div><a target="_blank" href="https://tutoandco.colas-delmas.fr/developpement/inserer-carte-google-maps-wordpress/?utm_source=jsfiddle&utm_medium=website">Voir le tuto complet</a></div></div>';

  Mrk.addListener('click', function() {
    infowindow.setContent(Cnt);
    infowindow.open(map, Mrk);

  });
}

function setMarkers() {
  console.log("setMarkers")
  for (var i = 0; i < points.length; i++) {
    var point = points[i];
    var contentString = '<div class="marker-infowindow">' + '<h2>' + point[0] + '</h1>' + '<div><a target="_blank" href="https://tutoandco.colas-delmas.fr/developpement/inserer-carte-google-maps-wordpress/?utm_source=jsfiddle&utm_medium=website">Voir le tuto complet</a></div></div>';

    var marker = new google.maps.Marker({
      position: {
        lat: point[2],
        lng: point[3]
      },
      map: map,
      title: point[0],
      loc_id: point[4],
      loc_txt: contentString,
    });
   ...