var marker1 = { lat: 13.686867, lon: 100.426157 };
var marker2 = { lat: 13.712259, lon: 100.457989 };

var distance = longdo.Util.distance([marker1, marker2]);

The following example requests the starting point and destination,in Web service:

https://api.longdo.com/RouteService/json/route/guide?flon=100.426157&flat=13.686867&tlon=100.457989&tlat=13.712259&mode=t&type=25&locale=en&key=[YOUR_KEY_API]

{
  "meta": {
    "from": {
      "lon": 100.426157,
      "lat": 13.686867
    },
    "to": {
      "lon": 100.457989,
      "lat": 13.712259
    },
    "config": "t25ennull"
  },
  "data": [
    {
      "fdistance": 1.784942,
      "tdistance": 27.394072,
      "id": 87863819,
      "interval": 400,
      "penalty": 30,
      "guide": [
        {
          "name": "Kallapraphruk Rd.",
          "turn": 4,
          "distance": 4474, //Section distance in meters
          "interval": 467
        },
        {
          "name": "Ratchaphruek Rd.",
          "turn": 2,
          "distance": 20, //Section distance in meters
          "interval": 1
        }
      ],
      "distance": 4494 //Distance in meters
    }
  ]
}