如何在google地图中添加获取方向选项

<script src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY&libraries=places"></script>

<div id="map"></div>

function initMap() {
  var map = new google.maps.Map(document.getElementById('map'), {
    center: {lat: YOUR_LATITUDE, lng: YOUR_LONGITUDE},
    zoom: ZOOM_LEVEL
  });
}

function initMap() {
  var map = new google.maps.Map(document.getElementById('map'), {
    center: {lat: YOUR_LATITUDE, lng: YOUR_LONGITUDE},
    zoom: ZOOM_LEVEL
  });

  var directionsService = new google.maps.DirectionsService();
  var directionsRenderer = new google.maps.DirectionsRenderer();
  directionsRenderer.setMap(map);

  var request = {
    origin: '起点地址',
    destination: '终点地址',
    travelMode: 'DRIVING' // 交通方式，可以是DRIVING（驾车）、WALKING（步行）、BICYCLING（骑行）或TRANSIT（公共交通）
  };

  directionsService.route(request, function(result, status) {
    if (status == 'OK') {
      directionsRenderer.setDirections(result);
    }
  });
}