JSFiddle - React, Tailwind, and code Playground

HTML

<div id="map"></div>
    <script async defer
        src="https://maps.googleapis.com/maps/api/js?callback=initMap"></script>

CSS

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

JavaScript

function initMap() {
     var latlng = {lat: -25.363, lng: 131.044};
     var markerArr =[
       {
         text:'1',
         latlng:new google.maps.LatLng({lat: -25.363, lng: 131.044}),
       },
       {
         text:'2',
         latlng:new google.maps.LatLng({lat: -25.362, lng: 131.044}),
       },
       {
         text:'3',
         latlng:new google.maps.LatLng({lat: -25.361, lng: 131.044}),
       },
       {
         text:'4',
         latlng:new google.maps.LatLng({lat: -25.363, lng: 131.043}),
       },
       {
         text:'5',
         latlng:new google.maps.LatLng({lat: -25.363, lng: 131.044}),
       },
       {
         text:'6',
         latlng:new google.maps.LatLng({lat: -25.363, lng: 131.042}),
       },
       {
         text:'7',
         latlng:new google.maps.LatLng({lat: -25.363, lng: 131.044}),
       },
     ];
     var map = new google.maps.Map(document.getElementById('map'), {
       zoom: 16,
       center: latlng
     });
     var infowindow = new google.maps.InfoWindow({
     });
     
     markerArr.map(function(e, i, arr){
       e.overlaped = arr.reduce(function(sum, x){
         if ( e.latlng.equals(x.latlng) ) sum++;
         return sum;
       },0);
       addMarker(e)
     });
     
     var i = 0;
     function addMarker(_){
       var latlng = _.latlng;
       var text = _.text;
       var overlaped = _.overlaped;
       
       var marker = new google.maps.Marker({
         position: _.latlng,
         map: map,
         label: String(overlaped),
         zIndex: 0
       });

       marker.addListener('click', function(e) {
         infowindow.setContent(text);
         infowindow.open(map, marker);
         this.setZIndex(--i);
       });

     }
   }