Como posso obter a latitude e a localização de um cliente fazendo com que ele coloque um marcador no google maps?

 function initMap() {
  var uluru = {
    lat: -25.363,
    lng: 131.044
  };
  var mapDiv = document.getElementById('map');
  var map = new google.maps.Map(mapDiv, {
    zoom: 8,
    center: uluru,
    clickableIcons: true,
  });

  google.maps.event.addListener(map, 'click', function(e) {

    if (map.getClickableIcons()) {
      var Latitude = e.latLng.lat();
      var Longitude = e.latLng.lng();
      // add your new marker with this info.
      var marker = new google.maps.Marker({
        position: {
          lat: Latitude,
          lng: Longitude
        },
        map: map,
        draggable: true,
      });
      map.clickableIcons = false;
      // get latitude and longitude after dragging:
      google.maps.event.addListener(marker, 'dragend', 
      function(marker){
           var latLng = marker.latLng; 
           currentLatitude = latLng.lat();
           currentLongitude = latLng.lng();

 }); 


    }
  });
}

/* Always set the map height explicitly to define the size of the div
 * element that contains the map. */

#map {
  height: 100%;
}

/* Optional: Makes the sample page fill the window. */

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

<div id="map"></div>
<!-- Replace the value of the key parameter with your own API key. -->
<script async defer src="https://maps.googleapis.com/maps/api/js?key=AIzaSyCu8vqg35dD4fNfxlI8ICoycehbL0F6bis&callback=initMap">
</script>