containsLocation not working

Question

I'm trying to retrieve a boolean result using 'google.maps.geometry.poly.containsLocation', the problem is than isnt returning nothing, I don't know if I need to called it inside of a eventListener, but when I try to called it starts saying that 'pos' is undefined, then when I intialize pos, it says that "lng" is not defined, something is wrong with my code or I'm not doing it the right way.

JS:

var map;

function initMap() {
    map = new google.maps.Map(document.getElementById('map'), {
    center: {lat: 41.185083, lng: -8.698814},
    zoom: 12,
    mapTypeId: google.maps.MapTypeId.TERRAIN
  });


  var infoWindow = new google.maps.InfoWindow({map: map});
  // Try HTML5 geolocation.
  if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(function(position) {
      var pos = {
        lat: position.coords.latitude,
        lng: position.coords.longitude
      };


      infoWindow.setPosition(pos);
      infoWindow.setContent('You are Here.');
      map.setCenter(pos);
    }, function() {
      handleLocationError(true, infoWindow, map.getCenter());
    });
  } else {
    // Browser doesn't support Geolocation
    handleLocationError(false, infoWindow, map.getCenter());
  }



   // Define the LatLng coordinates for Zone.
  var zone_Coords = [
    {lat: 41.194975, lng: -8.683102},
    {lat: 41.183693, lng: -8.703740},
    {lat: 41.205572, lng: -8.717563},
    {lat: 41.203185, lng: -8.690135},
    {lat: 41.194975, lng: -8.683102}
  ];

   // Construct the Zone.
  var zone = new google.maps.Polygon({
    paths: zone_Coords,
    strokeColor: '#023bca',
    strokeOpacity: 0.8,
    strokeWeight: 2,
    fillColor: '#0748eb',
    fillOpacity: 0.35
  });

  zone3.setMap(map);

var isWithinPolygon = google.maps.geometry.poly.containsLocation(pos, zone);
    console.log(isWithinPolygon);

}

function handleLocationError(browserHasGeolocation, infoWindow, pos) {
  infoWindow.setPosition(pos);
  infoWindow.setContent(browserHasGeolocation ?
                        'Error: The Geolocation service failed.' :
                        'Error: Your browser doesn\'t support geolocation.');
}