谷歌地图V3,如何获得多个目的地的最佳行车路线列表？

// 创建一个地图对象
var map = new google.maps.Map(document.getElementById('map'), {
  zoom: 10,
  center: {lat: 31.2304, lng: 121.4737}
});

// 创建一个DirectionsService对象
var directionsService = new google.maps.DirectionsService();

// 创建一个DirectionsRenderer对象
var directionsRenderer = new google.maps.DirectionsRenderer();
directionsRenderer.setMap(map);

// 指定起点、终点、途经点、路线限制、路线优先级等参数
var waypoints = [
  {location: '上海'},
  {location: '北京'},
  {location: '广州'}
];
var request = {
  origin: '深圳',
  destination: '成都',
  waypoints: waypoints,
  optimizeWaypoints: true,
  travelMode: 'DRIVING'
};

// 请求路线数据
directionsService.route(request, function(response, status) {
  if (status === 'OK') {
    // 在地图上显示路线
    directionsRenderer.setDirections(response);
  } else {
    window.alert('Directions request failed due to ' + status);
  }
});