如何使用mapbox-gl-directions设置起点和目的地？

<script src='https://api.mapbox.com/mapbox-gl-js/v2.6.1/mapbox-gl.js'></script>
<script src='https://api.mapbox.com/mapbox-gl-js/plugins/mapbox-gl-directions/v4.1.0/mapbox-gl-directions.js'></script>
<link href='https://api.mapbox.com/mapbox-gl-js/v2.6.1/mapbox-gl.css' rel='stylesheet' />
<link href='https://api.mapbox.com/mapbox-gl-js/plugins/mapbox-gl-directions/v4.1.0/mapbox-gl-directions.css' rel='stylesheet' />

<div id='map'></div>

mapboxgl.accessToken = 'YOUR_ACCESS_TOKEN';
var map = new mapboxgl.Map({
  container: 'map',
  style: 'mapbox://styles/mapbox/streets-v11',
  center: [lng, lat],
  zoom: 12
});

var directions = new MapboxDirections({
  accessToken: mapboxgl.accessToken
});

map.addControl(directions, 'top-left');

directions.setOrigin([lng1, lat1]);
directions.setDestination([lng2, lat2]);