Help with my project ionic1 its so basic but i have issues about http.post and json data

ionic-v1
1

Hi guys, i have very basic project that i must be finish in two days but i have some issues.

My ControllerJs Code;

$scope.dataBack={};

$scope.calculate = function(a,b){
console.log("Start: "+ a, "Finish: "+ b);

 $http.post('https://maps.googleapis.com/maps/api/distancematrix/json?units=imperial&origins='+a+'&destinations='+b+'&mode=driving&departure_time=now&traffic_model=optimistic&key=AIzaSyD4Q7mPb9XhS5i0KvgsCfi-ahKB-rooqOI')
.then(function(data){$scope.dataBack = data;
});

};

The question is, there is Google APİ above as you can see and ı want to take a single data from this APİ.
This api turns JSON back.ım trying to reach a “value” data of this JSON but ı cant.

ım coding like ;
console.log($scope.dataBack.rows[0].elements[0].duration_in_traffic.value);

but it turns back error about tha code above.

How am i suppose to do the JSON convert part? I think the problem is about JSON.
Please help me thanks.

EDİT: Btw the output of link is something like that;

{
   "destination_addresses" : [ "Rize, Rize Merkez/Rize, Türkiye" ],
   "origin_addresses" : [ "Ordu, Türkiye" ],
   "rows" : [
      {
         "elements" : [
            {
               "distance" : {
                  "text" : "204 mil",
                  "value" : 328881
               },
               "duration" : {
                  "text" : "4 saat 48 dakika",
                  "value" : 17270
               },
               "duration_in_traffic" : {
                  "text" : "4 saat 32 dakika",
                  "value" : 16315
               },
               "status" : "OK"
            }
         ]
      }
   ],
   "status" : "OK"
}