This gist is used in medium article

dynamic-map-marker.js

 let mapMarker = null;
                
 let map;
 map = new google.maps.Map(document.getElementById("map"), {
   center: { lat: 28.3949, lng: 84.1240 }, // :nepal:
   zoom: 6,
 });

 map.addListener('click',function (e){
      let marker = new google.maps.Marker({
                 position: {lat: e.latLng.lat(), lng: e.latLng.lng() },
                 map: map, //map object 
                 title: 'Dynamic Marker,click on map to change marker location'
               });

     if (mapMarker) mapMarker.setMap(null);
     mapMarker = marker;
});