_testes.html

<script>
function initMap() {
  var map = new google.maps.Map(document.getElementById('map'), {
    zoom: 4,
    center: {lat: -24.345, lng: 134.46}  // Australia.
  });

  var directionsService = new google.maps.DirectionsService;
  var directionsDisplay = new google.maps.DirectionsRenderer({
    draggable: true,
    map: map,
    panel: document.getElementById('right-panel')
  });

  directionsDisplay.addListener('directions_changed', function() {
    computeTotalDistance(directionsDisplay.getDirections());
  });

  displayRoute('Perth, WA', 'Sydney, NSW', directionsService,
      directionsDisplay);
}

function displayRoute(origin, destination, service, display) {
  service.route({
    origin: origin,
    destination: destination,
    waypoints: [{location: 'Adelaide, SA'}, {location: 'Broken Hill, NSW'}],
    travelMode: 'DRIVING',
    avoidTolls: true
  }, function(response, status) {
    if (status === 'OK') {
      display.setDirections(response);
    } else {
      alert('Could not display directions due to: ' + status);
    }
  });
}

function computeTotalDistance(result) {
  var total = 0;
  var myroute = result.routes[0];
  for (var i = 0; i < myroute.legs.length; i++) {
    total += myroute.legs[i].distance.value;
  }
  total = total / 1000;
  document.getElementById('total').innerHTML = total + ' km';
}
</script>

<script src="https://maps.googleapis.com/maps/api/js?key=AIzaSyDouIscSiDxLl_Ug9VL3Bb9mVU1WFj8UKg&libraries=places&callback=initMap"
        async defer></script>