JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://maps.googleapis.com/maps/api/js?v=3.exp&amp;sensor=false"></script>
          ahoj
<script src="https://maps.googleapis.com/maps/api/js?v=3.exp&sensor=false"></script>
    <div id="map-canvas"></div>

CSS

html, body, #map-canvas { xwidth: 100%; height: 100%; margin: 0; padding: 0; }
#map-canvas { border: solid red 1px; }

JavaScript

//alert(1);  
//alert(typeof google.maps.LatLng);
var mapOptions = {
    zoom: 6,
    center: new google.maps.LatLng(-34.397, 150.644),
    mapTypeId: google.maps.MapTypeId.ROADMAP
  };

//alert(2);
  map = new google.maps.Map(document.getElementById('map-canvas'),
      mapOptions);
alert(map.getZoom())
  map.fitBounds(new google.maps.LatLngBounds(new google.maps.LatLng(48.5,12.1), new google.maps.LatLng(51.1,18.9)));
//map.setZoom(2);
if (1) 
google.maps.event.addListenerOnce(map, 
                                  //'idle',
                                  'zoom_changed',
                                  //'bounds_changed', 
                                  function() {
        //alert('it definitely works');
        alert('ahoj' + map.getZoom());
        map.setZoom(2);
});